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Appropriate Mixes for Adobe

Quentin Wilson and Associates, specializes in solar adobe design and construction. He grew up in the South Valley of Albuquerque, New Mexico where he watched adobe bricks being made. In the fifth grade, he made miniature adobes on cookie sheets in his mother’s oven in order to construct house models for a class assignment. By age thirteen he made full-sized adobes in the back yard and ruined the grass. Later, he traveled a bit, went through the Army, and graduated eventually from the University of New Mexico with a major in physics, minors in math, chemistry, and education in 1970. After teaching high school two years and community college math for three more, Quentin moved into professional solar adobe construction in 1976 as the Project Manager and Instructor for the Sundwellings Demonstration Project at Ghost Ranch, Abiquiu, NM. He became a licensed general contractor in the State of New Mexico in 1982. He has been building homes and teaching seminars and workshops ever since. In the fall of 1995 he established and taught the full-time Adobe Construction Program at Northern New Mexico Community College. His website, quentinwilson.com, lists the course schedule and many other resources related to working with adobe.

Q: What is the best mix for good adobe blocks?

A: Mainly you want 30% clay or less. The rest can be sand, silt and stuff. The jar test is rarely straightforward and easy to read. The best test is to make some test bricks. Too much clay and the bricks crack and that is when you need straw and that got widely publicized by Moses up in Egypt. I would have just gone up the wadi and gotten sand and forgotten about Pharaoh's straw.

The best measure of water is your judgement of what is workable. And that judgement comes quickly after several tries. It can be pretty slurpy if you have enough forms so that you can leave mud in them overnight to start drying and then pull the forms the next day. Worldwide most folks only have enough wood to make one form for four adobes and that is just about the amount that comes out of a worldwide standard wheelbarrow. With one form which has to be pulled right away to get ready for the next load, then the adobe mud needs to be stiffer. When the form is lifted, if the bricks slump down, then just put them back in the wheelbarrow or mixer and add more dirt to stiffen it up.With adobe there is always a second chance. Or third or...

Let the bricks dry in the sun for a day or two. As soon as they can be turned on edge, turn them on edge. If they don't like to balance on edge, do a herring bone pattern with them touching each other to stay up. On edge they need about a week of drying. Then stack them out of the way so that you can make more bricks. Once stacked they should dry/cure for four weeks before use.

Once a few test bricks are made you can test them for compressive strength and at the same time for modulus of rupture by dropping them from knee height. If the bricks survive, they are good bricks. If they break you might be lucky and can use halves or thirds to fill in smaller spaces. Basically if you have a frame to fit them into, as long as you can pick them up and get them into the frame, they will work. We never bother with a test for hardness. Germans do and it's in their DIN Standards. Now, probably the whole EU uses the tests. But the drop test does all that you need to know.

Q: I live in Santa Fe, NM and am interested in constructing a wall around my property made of adobe bricks. I think I have the patience to make all the bricks myself (good estimate of about 4,635 bricks for five foot height). Does anybody near my area carry bags of material to make bricks myself that I can just "add water" to?

A: I don't think anyone has it bagged. For 4500 adobes each weighing about 30 pounds you will need 135,000 pounds of material. That's a mere 67.5 tons! A heavily burdened single axle dump truck can handle 10 tons so we are up to almost 7 dump truck loads. You will need another 20% of that amount to make the mortar to put the wall together. Many Santa Feans will claim to have the perfect dirt for adobes but I would prefer to get it from someone who has actually made them successfully.

Q: I want to make miniature adobe houses for my son's Santa Fe train city. I cannot seem to find any specific directions. I noticed that your article on this site said you had made them before. Can you help me with instructions?

A: Little adobes can be made many ways. The simplest might be to fill a cookie sheet with mud. It is easiest if the cookie sheet has low sides around it, about a half inch. Then the mud can easily be scraped off level with a knife, trowel or short board. Little adobes of most any size can then be cut with a pizza rolling knife. An inch wide by an inch and a half long is a good size. Then put the mud in the oven at about 225 degrees for 10 to 20 minutes. The bricks may have stuck together a bit but they will break apart easily enough. The mud mixture should be mostly sand - about 70% and the rest clay. Many soils out your back door will work but sometimes a little sand can be added if the soil has too much clay. It is clay that causes bricks to crack. Just fool around a bit until an appropriate blend is discovered.

Q: I am a thesis student of Architecture at Auburn University. I am pursuing my thesis in the Rural Studio, which focuses on Green buildings and housing the unfortunate poor of Hale County. Our project is in Lee County, AL, and consists of transitional housing for persons with disabilities. Me and my team are interested in the construction methods of adobe bricks and cast earth. The soils around locally are high in clay content. I was wondering what construction methods would work best in Alabama. As well as would these be viable methods. Any information that you could provide would be greatly appreciated.

A (Kelly): I have been aware of and impressed with the work of the Rural Studio and Sambo. I am very sorry to see that he died, but glad that his work will continue. I have much respect for what you are doing. I would say that adobe in particular would be an appropriate material for you to work with. The caste earth really requires the use of heavy equipment and an experienced crew. A few people can make adobe bricks and lay them very inexpensively and create substantial and comfortable housing. I suggest that you see if you can locate a cinva ram press to make the adobe blocks, since it is fast and makes very solid blocks without a lot of drying time and no need for forms. The clay content of the soil needs to be around 20% to 30%, so you might do a little test with some of the soil in a jar of water, shake it and let it all settle for a few hours to see exactly how much clay there is in the soil (the clay will form a layer on top, over the heavier soil particles). You may have to add some sand to the mix. Good luck with your project.

Q: I have spent some time researching earthship homes and was seriously considering that but the research I've done today has me considering adobe. As they seem to be a bit easier perhaps, in construction. Tire pounding would probably be good exercise but I don't know if I'm up to it. Ha! I have 10 acres in the country and plenty of dirt but not sure if it's "the right dirt" or does it matter? Probably just mix with straw? I am curious.

A: 30% clay, 70% sand, gravel, decomposed granite makes the perfect brick. As little as 10%clay will also work. Some silt can be tolerated in the mix. Straw is only needed to keep the bricks from cracking if there is more than 30% clay. Too bad Moses didn't know that. Maybe its better. History would have been different.

C: I thought I would add a little fodder to the mix. In regard to historical inaccuracies. I am guilty of confounding a situation myself by mixing arrogance and ignorance in the same breath, so..... my job is to come and reason together in peace. The following is from your link and is simply, completely, incorrect. Many of the mixes used, are almost as old as the dirt we stand on, and passed from generation to generation. In regard to Mosses. Thanks, a retraction suggested, but not necessary. Regards of bantering.

R: The Adobe Construction Program operates from Northern New Mexico College at its El Rito, New Mexico Campus. You should come for a visit and we can exchange what we know in the form of adobe bricks that we can make from various mixes. I feel strongly that adobe should be made as simply as possible with the materials at hand. Throughout history there have been efforts to introduce additional constituents into adobe mixes: gypsum, lime, Portland cement, emulsified asphalt, straw, manure, horsehair, grasses, molasses, and so many more things. Usually the person claiming that the extra ingredient is absolutely necessary also happens to be the person who ever so kindly will sell that material to the brick maker. Pharaoh could control Moses and the Israelites ability to build homes by granting or withholding straw. Seems to me to have been one of the earlier recorded incidents of government interference in the lives of owner-builders. Along the Nile, the frequently flooded farmland where the Israelites lived, the surface soil is very high in silt and clay and low in sand and gravel. Bricks made from this soil would crack without the addition of straw but another solution would have been to go up the wadis (arroyos) where there would have been abundant sand to temper the mix to produce fine, strong, non-cracking adobe bricks. Further up the Nile, the Nubians made fine adobes with no straw.

Q: Aloha. Currently residing in up country Hawaii. Have experience in rammed earth from a former life in Tucson, but am curious about "field" tests for compaction of native soils. There are 5 different bioregions on the island of Maui alone and I am only hand tamping the forms so far. So basically I want to hand tamp local stabilized soils for the purposes of sculpture, not structure. Any thoughts on how to check my available soils before I hand ram something that lacks the desired integrity?

A: Small samples. Squash em, kick em, leave em in the rain.

Q: I am busy preparing a business plan to build low cost toilets using earth blocks compressed with 7% cement, do you think I can use those type of blocks to reinforce the pit which will be 2m3, do you think the small toilet can collapse after 2 or 3 years because of the daily wet environment, I did not find any information on the internet concerning compressed blocks under wet environment.

A: These blocks might work. I am very happy to hear that you would be using them to build the toilets. However, it is known that CEB's sometimes "blossom," another word for expanding, when they get wet. This is because there are a lot of unresolved interior stresses due to the normally ferocious pressure with which the blocks are made. A block that is subject to moisture might be better made with a higher cement content and made with the compression force lowered.

Each and every soil reacts differently to the introduction of cement which is basically not compatible with the clay content. For this reason the book, Soil-Cement, It's Use in Building was developed by the United Nations in 1964 and was used as a handbook for Peace Corps volunteers making bricks around the world.It was prepared and first issued in Spanish by the Inter-American Housing and Planning Center, Pan-American Union, Department of Social Affairs. Later versions in French and English were prepared by the United Nations. In English it is United Nationals Publication Sales Number 64.IV.6. ($1.50) It spends considerable time on figuring cement/soil ratios appropriate to different soils.

Q: I am making stabilized adobe (adding asphalt emulsion) in Todos Santos, B.C.S. Mexico. I want to leave the adobe exposed on the outside and have flat roofs. Will the stabilized adobe hold rain? Do I need to add some sort of water sealant?

A: Adobe with about 4% asphalt is quite waterproof. In the USA the asphalt is quite emulsified through chemical magic and mixes easily with water. The asphalt I have seen in Mexico is not as thoroughly emulsified and has a bit of a kerosene smell even after the adobes have cured. It is sometimes referred to as cut asphalt instead of emulsified asphalt. The walls will work well in areas that have rainfall under 50cm annually if you use asphalt in the mortar at the same rate as the adobes. Do not put on an exterior sealant. Many types of sealants have been tried and if they do not breathe, any moisture that gets into the adobe cannot get out and breaks the bond of the sealant at the surface of the adobe. Asphalt will do the job. With your project, you might wish to join our adobe discussion group at: <adobe-subscribeATyahoogroups.com>

Q: I was wondering how much asphalt emulsion is needed as a ratio to make mud cement and how much does a 50 gallon can of asphalt emulsion cost ..

A: Each soil will react differently to asphalt emulsion so in New Mexico the definition of a stabilized adobe is a functional definition. That is, an adobe placed on a porous, water saturated surface for seven days may absorb no mare than four percent moisture by weight. Adobe producers will tell people that they use 2 to10 percent asphalt emulsion but do not mention if that is measured by volume or weight. I find that 8 to 16 liquid ounces is about right to stabilize a cubic foot of my soil's adobe mud. That is about 1/2 to 1% by weight. It is not fully stabilized but will give enough protection to preserve the adobe for my lifetime. Another way to add is to put 5 gallons of emulsion into a 55-gallon drum and fill it the rest of the way with water. That way the water has 10% asphalt. It is a little nicer to work with than full strength emulsion.

The cost of 55 gallons of asphalt had been about $75 until the prices of oil products began to go up the last couple of months. My guess is that it is well over $100 by now. A source of emulsified asphalt in New Mexico is Elf Asphalt on North Edith Street in Albuquerque. Their minimum sale is by the 55 gallon container. You have to have your own barrel hopefully one with a removable top. Plan on splashing some asphalt on the cab of your pickup truck as a badge of honor.

Q: I live in the Pasadena area of southern California and am interested in working with stabilized adobe first in a low retaining wall and perhaps more ambitious projects later. Where can I buy the emulsified asphalt in relatively small quantities (1 gal -5 gal) locally? Thanks in advance for the help.

A: If there is an Elf Asphalt plant anywhere in your area, they may sell you five gallons of emulsified asphalt. There might be some other bulk asphalt plant that supplies road or driveway repair contractors. If not, some formulations of roof asphalt - sometimes called cold process - are emulsified. One just has to read the can to see if it can be thinned with water. A lot of the original work with adding emulsified asphalt to adobes was done in Southern California. Largely a group of retired chemists from Chevron.

Q: I live in Northern California and want to build an outdoor adobe oven. The soil here is fairly organic with lowish clay and sand content. Local construction supply stores give me a blank stare when I ask about availability of adobe type soils.

A: Sand and gravel producers usually have something that will work. They might call it crusher fines or crusher trash. Old fashioned base course worked great but at least in New Mexico base course now has less clay and will not clump together. You are looking for a soil that has 30% clay and 70% sand. Gravel particles can be tolerated up to 1- or 1-1/4 inch diameter in adobe bricks. You can use far less clay if you are going to stucco over the horno for weather protection. You can't use much more clay without experiencing cracking. 30/70 also makes a good mortar to stick it the adobes together. For mortar you might find it useful to screen the material through a 3/8- or 1/2-inch screen.

If a sand and gravel producer can't help you, the material is on your property. You just have to dig below that pesky top soil down to sand and clay and gravel strata below. Or find a riverbed or wash nearby. Or make friends with a gravedigger. The Spanish who put the California in California could make adobe bricks most any where in the state.

Q: I am interested in building an adobe exterior wood fired oven for outdoor use in the Boston, Massachusetts area. I can not find any one who has any knowledge of adobe availability out here and wanted to know what other materials may be suitable to create the shell of the oven specifically the clay component of the mixture, is pottery type clay appropriate or something else that is available in larger size formats?

A: A mixture of 30% clay and 70% sand/gravel will work. Sometimes that is called base course at a gravel pit. Pit run or crusher trash will usually also work. We are discussing hornos (adobe ovens) at the moment at http://groups.yahoo.com/group/adobe/ An English style oven was built in MA or ME and was featured on the PBS program the 3000-Mile Garden a few years back.

Q: Are you familiar with liquid glass added to adobe as a stabilizer? If so, where can I get some? I'm building in Terlingua Texas, which is a desert.

A: I thought that I had heard everything but this one is new to me. You are near Simone Swan and her adobe dome and vault projects at Presidio. Not to mention Pat with her adobe at the end of Twisted Road at one of the villages between Ter and Pre. I will ask my friends about liquid glass which reminds me that we learned in Science Class that glass was a liquid.

C: Water glass is probably what she was describing. Sodium silicate?

A: My guess is that waterglass without modification will not do the trick. Still no one with actual experience with the material with respect to adobe.

Q: Can Compressed Earth Blocks (CEB) be stabilized in such a way that they can be directly exposed to the weather for use in home-building, retaining walls, driveways, etc.? If so, what is the stabilizer to use, and if not what is the best stabilizer for moisture protection and what other steps must you take to protect the walls?

A: Most CEB's are stabilized with cement. There have been problems with exposed walls even with cement. If the walls get wet, some of the pressure of unrelieved stresses at the particle level in the CEB's is released and the bricks "blossom." That's another word for expanding and flaking apart. My own solution would be to stucco exterior wall surfaces of CEB's. CEB practitioners might have more ideas.

Q: I intend to stabilize the adobe with pozzuolana ash like Rice Husk Ash or Silicafume. Do you have any experience on this problem? Please give me some advice! Will I succeed?

A: I have never tried this so am unable to predict the outcome. I have always been happy with unstabilized adobes. Just back from Cappadocia in Anatolia where there are 3- to 4-thousand year old adobes without stabilization. They have had constant maintenance even in that low rain climate. However, nearly everything works with adobe so with a little experimenting with ratios, you should get a workable brick.

Q: I live in Barbados where coral dust is available. I am wondering if this can somehow be used in the construction of adobe brick?

A: Adobe needs aggregate such as sand, gravel, or stone as the component that gives strength. It also needs something to provide cohesion, namely clay. The coral dust might provide the aggregate part or perhaps it has stickiness and can act as the clay component. I have no experience with coral other than to observe it in some Navajo jewelry along with turquoise. If the coral has no sticky ness, then it should act well as an aggregate. You would then need to find a clay course and there should be some in the Barbados. You would only need about 9% of the total weight of the brick. It would not be very waterproof. 30% would be better. I do know that there is some adobe construction in the SE part of Jamaica. If the coral provides the sticky ness, then you only have to find lots of sand to add to it to get a great brick. Just try fooling around with the coral dust to see what happens.

Q: I live in NE Georgia, and I would love to make a patio out of adobe block. If I placed the blocks on a well draining foundation of gravel and sand, and 'sealed' the blocks with linseed oil, and reinforced the adobe block with cement, would these blocks withstand wet weather and winter conditions? Also, would it make a difference if this patio was covered? I would like to mortar or thinset the blocks together to prevent any weeds from growing between the blocks.

A: Linseed won't work. Cement will help at about 6% of the total block weight. It is always hard to predict how any particular block will handle moisture and freezing. It can even be a problem for concrete. Indeed the blocks can be expected to survive better if the patio is covered. Put the adobe blocks together with a regular mason's mortar or a mortar made just like the blocks themselves. Thinset is not enough bedding for adobes which should be in a 3/4-inch mortar bed.

Q: I live in central California. I am trying to find a source in CA for Adobe soil/clay. Do you know of anyone?

A: Many of the soils in the drier parts of central California are perfect for adobe. The best adobes are made with 30% clay and 70% sand. Silt up to 40% can be tolerated although it makes no contribution to the brick. The same goes for small amounts of organic matter. As little as 7% clay will work and up to 45% clay will also work but the bricks are more likely to crack without the addition of straw or some sort of fibrous binder.

The world's largest adobe producer was Hans Sumpf in the Madera area. They have slowed down their adobe production to increase their tile output. Hans Sumpf Adobe (Bobbie Kemp Van Ee), 40101 Avenue 10, Madera, CA 93638; 559-439-3214

Lots of times, the unwanted materials at a gravel production operation are perfect for making adobes. In fact, the Hans Sumpf story which I don't remember well had something to do with just trying to figure out what to do with a mountain of dirt left over from some industrial or agricultural project.

Q: I live in NY and would like to build a brick/clay oven. In the Northeast here we have very little access to Adobe building materials but I do have access to potters clay as my wife is a potter and receives regular deliveries. What proportions of clay to sand would be suitable to use as mortar. And then the proportions for using it as a plaster for finishing the inside and outside?

A: English immigrants in the 1830's to 1870's built sun-cured adobe brick homes in Geneva, NY and the surrounding area. English traditional clay ovens are often half-barrel shape with a roof over it for rain protection. I saw it in a segment of the PBS series, The 3000-Mile Garden which involved gardeners in England and Massachusetts. I could never figure if the oven was in UK or US. Baking ovens in the SW USA are dome shaped. 30% clay and 70% sand would be perfect.

Q: I've been experimenting making some blocks, and lab tests have shown me that my soil is 74.4% sand, 14.0 silt and 11.6% clay. I read on your site that as little as 10% clay can work. Do you think my soil has too little clay? I added 10% by volume of Portland cement. I dropped the bricks from shoulder height and they broke up after three drops. I am considering adding an extra 10% of clay, but I'm wondering if it is necessary? I'm almost ready to start building and so I obviously want to be sure my soil is ok. I'll be using traditional methods as opposed to pressing machines.

A: The NM Code requires adobe to have 300 psi crush strength and a modulus of rupture of 50 psi. PG McHenry, the author of Adobe Build It Yourself , determined that a drop from about knee height was the equivalent of the 300 and 50 psi laboratory tests. So if it takes a shoulder height drop for you bricks, I would say that they are more than strong enough. Don't add Portland cement. Portland and most clays are not compatible and so the first bit of cement added goes into overwhelming the clay and then the balance of the cement takes over the bonding duties. The Peace Corps had a manual, Soil-Cement, Its use in building mainly to teach volunteers how to negate the power of clay. You could add some clay, but I just don't think it is necessary.

Q: Your reply leads to to me further requiring your knowledge regarding stabilization. If I don't use cement how should I stabilize my adobes? In one batch of tests I made one brick with 10% cement, one brick with 10% lime and one with neither clay not lime. After three weeks drying I soaked them in water for a couple of days. The brick without cement and lime dissolved within minutes and the others remained virtually unchanged. Which led me to believe that cement or lime would do a good job against rain damage. I have read from many sources (including your website) that cement is commonly used in adobes. Maybe I could use less cement (5%)? Or should I really use none. My doubts arise from the fact that the bricks I made without cement or lime broke up easier when dropped. And if so, how should I stabilize them? Is Lime ok as a stabilizer? Or is it also incompatible with the clay? Should I use asphalt emulsion for example? Having read that 20-30% clay is optimum, what disadvantages will be present in my blocks if my soil only has 11% clay? I shall be building in Texcoco, an hour away from Mexico City.

A: These days, emulsified asphalt is the preferred stabilizer. It may not be available in Mexico as the same formulation. The Mexican asphalt I have seen was "cut" asphalt which had a solvent rather than an emulsifier. It
will out-gas for a long time as the solvent evaporates. Cement and Lime might be your choice.

Another reason I don't like cement is that it takes more than its share of energy to produce. Should you make adobe at 10% cement levels, then with the thick adobe walls, more cement has been use than in "California Tilt-Up" concrete walls. The Californians routinely make walls for industrial buildings by casting them on the ground as a slab then tilting them into position. These walls are 4", sometimes a thin as 2". They use about 16 to 20% cement so if we adobe folks want to beat that we have to be very judicious in our use of cement. Besides, I ran a block plant over a couple of years and just plain had my fill of cement and lime so I may not be the most objective person around.

11% adobes will be very strong, not far from the strength of the 30/70 ideal brick. Once the house is built with a good foundation and a better roof, we hope to avoid the conditions found in a bucket. Lumber in those conditions will rot or at least mold and produce spores like crazy. Steel will rust. In short, most construction systems work hard to protect the wall system from moisture.

One solution is waterproof plaster. Another is to have porches and overhanging roofs that keep most rain off
the walls. About ten of my students are ready to hop on the bus to come down and help you. Friday and Saturday our high temperatures here were not quite 40 degrees F. The New York City contingent sends their regrets as the buses are not moving today.

Q: I didn't really understand from your reply whether as little as 5% cement might at least semi-stabilize my adobes? or should it be 10%. Also is the cement/adobe ratio normally referred to by weight or volume?

A: For the on-site builder, cement/sand/gravel/adobe ratios are based on volume. We just count the shovelfulls. If I was not clear, it was because I don't know for sure. Every soil acts a little differently to the addition of stabilizer. I think you just need to make some test bricks at 5 and 10%. If you can let them sit 28 days drop them in a tub of water. If they hold up for a couple of days, that's good enough.

Q: I'm a student from Milano, Italy and for my thesis I'm doing a project on low-cost houses. I decided to work with adobe because my project site is Ecuador, where this technology is traditional. I would like to know what do you think about adobe mixed with recycled paper (padobe) and if could be useful to use tires for the foundation of the house and if yes how can I do them.

A: We have worked with lots of things added to adobe here at Northern New Mexico College. It is my opinion that just plain adobe is the best material. Paper added to adobe adds fiber and in some instances increases the tensile strength. However, the bricks are more likely to absorb moisture out of the air and have elevated humidity. I do have a very personal bias and that is that homes constructed for poor people should not be experimental. Proven, long-standing technology is the choice for them. I prefer to keep the experiments in the laboratory.

Q: My soil is quite dusty but mixed with all sorts of sizes of stones and the like. What's the ideally sized screen to use for sieving? Is 1/2" ok? I'll be protecting the adobes from the elements using plasticized canvas, but I was wondering if I have to protect the mound of sieved soil from rain too? It's a low (11.5%) clay content, so would it clump after the rain?

A: This will work fine. Adobes can actually tolerate at least a few stones up to 1/3 the thickness of the brick.

I don't usually bother with covering the dirt but I am in a quite dry area most of the time. Each soil has its own personality and workability which you get to discover after working with it a bit.

Q: A friend of mine's father used to work for an adobe place in so cal in the 1960s. They used only clay and an oil called beechmo? beachmo? some of the homes that used these bricks are still standing with no outside clay wash or large overhang on the roof. Feedback would be great.

A: Bitumen, bituthene, pitch, brea, la brea, it could all get turned into beechmo. Probably different words for asphalt emulsion which began to see use in the late 50's in California.

C: I'm currently casting adobe block to use adding on to our existing adobe structure. I have just today purchased CSS Emulsified Asphalt for the bricks. I thought you might like to know where and how much the EA cost. I purchased the EA from Western Emulsions in Tucson, AZ for $7.00/Gal plus tax. I dealt with Jeff, and the transaction was simple and straight forward. I just wanted to share a resource, and spread the word on a company that will deal with the small guy.

Q: I am a Ph.D. research candidate working on "Efficacy of Selected Local Stabilizers - Rice-Husk-Ash, Straw & Cow Dung, on the Stability of Earth Buildings". What treatment(s) are possible/necessary for the straw & Cow Dung to avoid any adverse effect of their organic content on the earth material.

A: Fortunately, there are no adverse effects from straw or cow dung on earthen materials. Adobe bricks have been made with those materials throughout history. As for the Rice-Husk-Ash, I am unable to say since it is outside my experience. In New Mexico, wood ash has been historically used in adobe bricks. I would therefore guess that there would be no problem with the Rice-Husk-Ash addition.

Q: I live in SE New Mexico, and am trying to build a small adobe building before hopefully going on to something more ambitious. I intend to buy the blocks, but have been making test blocks looking for suitable soils for the mortar. The New Mexico building code says soils with visible alkali salts should not be used. What is an alkali salt? My blocks form a white powder on the surface when drying, especially where they've been touched. (They form white hand prints where I grabbed them to turn them upright to dry). Is this alkali salt? If so, what does it do to the adobe? And is there anything I can do to get rid of it? I have access to dirt that is almost pure clay, which when mixed with sand is making nice blocks. But even the rain puddles near this dirt leave a white residue when they dry.

A: Alkali salts is the white stuff on top of the ground that is left after ground moisture evaporates. It's in many places around SE NM. Sounds like just what you are seeing on your blocks as they dry out. The hand prints are a new wrinkle in the great mysteries of the universe. Might be useful in homeland security or could be turned into a new form of photography like the leaves on blueprint paper that many of us used to do in grade school. There must be mineral deposits in your clay and/or sand if your are seeing residue in the rain puddles.

I don't think there is anything you can do to get rid of it. I say keep on making bricks. Once they are fully cured drop them from knee height. If they survive, they are good. If they break try to find a softer surface to drop them on. If the bricks are strong when cured, then you do not have a problem in my opinion. Then just make sure you have a good foundation with tar, asphalt, or some really good waterproofing on top to stop any moisture from moving upward into the adobes. Also be diligent in your roof construction to keep the rain off. This is good advice for any wall whether adobe, wood, or steel.

Also look around your area to see if there are old adobe buildings. If they are there, then you should have no problems.

Q: My adobe home, in Southern California, was built in 1987, using adobe bricks from Hans Sumpf. For appearance, portions of the bricks were plastered over with about one inch of adobe plaster made with Hans Sumpf fine screened soil and asphalt emulsion stabilizer. Chicken wire was nailed to the bricks, to help hold things in place. Now, after almost 20 years the adobe plaster is deteriorated to a point where I want to replace all 5000 square feet of it. I can still get some of the screened dirt from Tom at Hans Sumpf even though they will be completely out of business by the end of this month. I've read your Q & A and found it the best source of information I've seen, but I have some further questions.

Part of the plaster is well protected by a 10 foot roof overhang but other parts are not, and they even extend down to the ground, but I don't want to change the design. Should I use the same asphalt emulsion stabilizer (5% by weight) that was used before? A fellow that you may have heard of, Gil Sanchez from Santa Cruz, will be helping me. He suggested using White (Elmer's) Carpenter's Glue. I'm not sure if it is better, how much to use or if it should be used in combination with the asphalt emulsion stabilizer. What do you think? Are there any other permeable binders that I should use instead? Who is currently a good source of asphalt emulsion stabilizer?

A: Wow! Gil Sanchez is the best there is.

I would stick with the asphalt emulsion stabilizer. The amount I favor is about 12 to 16 ounces per wheelbarrow. That's about a 3- to 4-cubic foot load in the wheelbarrow. Actually, I mix in a mixer but after several loads counting shovelsfull, I can judge how much is in the mixer before I pour it into the wheelbarrow. At that low rate of asphalt, the mixture is still moisture vapor permeable. It has held up well on the exterior of the church here in El Rito with some touch up over the past 20 years.

I have used Elmer's Glue but only on interior walls and then only when the soil was very sandy. Most good adobe mixes work on the interior without metal netting or any admixture. I would not use both stabilizers in the same mix. I get emulsified asphalt from Elf Asphalt which I think is nationwide. They supply to the highway and driveway repair industries. They may have quirky requirements in the amounts they will sell and into what kind of containers they will deal with. There might be other asphalt suppliers in your area.

Q: I have been working with paper clay the past 2 years and would like to make large unfired sculptures with adobe. I read that emulsified asphalt will water proof the adobe. I live in Mexico and have not found a source to buy this material. I wonder what you know of using this or some other method more accessible.

A: Depending on your dirt/clay, you can try portland cement or lime, both of which should be available in Mexico. Mexicans do produce asphalt that they add to adobes in some places such as around Juarez. It has some kerosene in it sometimes and is not much fun to work with. If you can find a paint manufacturer you might be able to get some of the acrylic latex that they use as a base for water paints. Or you can just buy some water based paint in a color that will work with your sculpture. Fish oil emulsion is also available in some places in Mexico. There is a lot of work with extracting the goo from prickly pear cactus and mixing it with clay. Back to emulsified asphalt, it is used a lot in highway asphalt repairs so if you can find an asphalt repair or construction firm, they might have it.

A (Kelly) : You can often buy an additive sold to stabilize white wash in Mexico that is called "resina", and I am pretty sure it is actually the acrylic latex that Quentin mentions.

Q: Can you give me an idea of the percentage of material to adobe I should begin with?

A: Emulsified Asphalt: 1 to 5%; Cement: 3 to 7%; Lime: 2 to 9%; Fish oil emulsion: 1 to 3%; Carpenters glue: 1/2 to 2%; Resina or latex/acrylic: 1/2 to 4%. Every soil is different in its clay/silt/sand ratios so it just takes fooling around. I can usually tell when the mud just begins to feel a bit more sticky. As soon as it will not slide easily off a trowel or shovel, it is too much. If it sticks to a trowel or shovel to begin with before any admixture, then there is too much clay and the bricks will probably crack. Then the soil needs more sand. There are whole books written about this such as the UN Handbook: "Soil-Cement, its use in building". See this page. Have fun.

Q: I live in southwestern Utah in a small community called Mt Carmel about 20 miles east of Zion National Park. I would like to build a home either using Adobe bricks or plastered mud. My question is does the muddy soil that when wet and sticks to my shoes, good enough for making Adobe? And how fast does Adobe melt when exposed to the elements. How should I slow this process down or stop it using natural materials from the environment?

A: Mormons built many adobe homes in the Georgetown area. There is now a walking history tour of about ten of those houses the elders built. If the muddy soil sticks to your shoes then there is certainly enough clay to make bricks. In fact there may be too much and the bricks will crack as they dry out. The solution is to add sand and/or straw to keep them from cracking. I prefer sand. In New Mexico and I imagine SW Utah an adobe wall exposed to what rain there is looses about 1" per twenty years.

A pitched roof with adequate overhang is one way to increase the lifetime. Mud plaster that is renewed every couple of years or cement/lime/sand stucco that lasts for decades are other solutions. There is a lot of interest in lime based plasters and you might have local sources of lime in the area. For that you need to find an old-timer who has worked with the local materials and can tell you where to find them and how to use them. If you have prickly pear cactus around they can be chopped up in a fifty-five gallon drum and left to percolate a bit. After a while a green sticky goo is produced that can be lifted out and added to mud to make a fairly waterproof plaster.

Q: Where do you live, New Mexico? And the bit about the chopped prickly pear is interesting. There are at least two varieties here. One is green the other purple.

A: I am in North-Central New Mexico. I teach the Adobe Construction Program at Northern New Mexico College in El Rito.

Most of the work with cactus and sometimes horse or cow manure plaster has been done in southern NM or in Presidio, Texas/Ojinaga, Mexcio where Simone Swan has hosted workshops through her Adobe Alliance. She has a home built with adobe vaults for ceilings/roofs and has been very interested in coming up with a waterproof plaster. She started with a lime stabilized plaster but did not feel it worked out. She removed it and replaced it with the cactus juice plaster.

We started to fool around with our local prickly pear cactus but we got so busy last May building what was then our largest dome that we forgot and let the cactus dry out. Therefore we really don't know how it compares to the great big juicy cactus ears around the US/Mexico border.

I would say that you might cut up purple and green cactus and put them in separate five-gallon buckets and cover them with water. After a week or ten days they should ferment and if you keep stirring daily it should turn into a gelatinous mess. Then you lift out the mess with some fork-like device and leave behind the spines. The gelatinous mess can then be used to make plaster and I think around a pint per wheelbarrow is a ratio for starting. Maybe a quart. Every soil is different in how it reacts to admixtures.

Then you just have to scientifically monkey around till you find a mixture that can be troweled, does not crack upon drying, and demonstrates an enhanced resistance to water erosion. It will not be perfect, but if you can go from standard soil mixtures which have a one- to three-year life expectancy on a wall to a five-year or greater life, then you have made progress.

Q: How does lime preserve an adobe?

A: I don't know. We only used it once in 1976 at Ghost Ranch for the Sundwellings and there appeared to be no difference between the naturals and the lime admixtures. It was no fun to shovel the lime into the mix since it was a fine powder and it is caustic. There are people out there writing books on the loveliness of lime in adobe plaster or just plain lime and sand plasters. I stick with just plain mud.

Q: I live in Michigan and am interested in building an adobe oven. I have access to clay / shale that is used to make fired brick. Would this material be a suitable substitute for adobe soil?

A: If it will make a fired brick without modification then is should make a fine adobe brick dried in the sun. We know of no adobe structures in Michigan. There are still thirteen adobe brick homes built by English settlers around Geneva, NY around the 1850's.
As long as there is a foundation which need be nothing more than gravel about 8 inches deep and mounded up above the surrounding ground level, the horno should work just fine.

Q: I live at 7600 feet in the high-desert of New Mexico(Taos). I am trying to use available resources and have a question about a particular earth recipe. My earth is virtually all clay and I have a lot of dried/aged horse manure. My tests show that a 50/50 mix does not crack, so how good would these bricks be? It seems similar to "straw clay" but is rather "horse clay", with smaller fibers. I would obtain enough sand to plaster over this with a more water resistant mix.
Thoughts?

A: I think that your use of horse manure is perfect. The closer to single fibers, the stronger the bond of straw to adobe. Big, heavy wheat straw is slippery and stiff and does not bond as well. Ancient cultures discovered it is a lot easier to let the horse do the work instead of chopping straw all day. Hassan Fathy thought that if the mud can sit for three days that the microbes present begin to make lactic acid which strengthens the adobe bricks. I am not sure this has ever been verified in a laboratory, but history is the best laboratory.

For your water resistant plaster, the higher the clay content, the more resistant the plaster. For some reason, traditional wisdom tells us that cow manure is better for this water resistant plaster mix than horse manure. The Australians say, "the fresher, the better." In Northern Mexico and at Simone Swans in Presidio Texas there is interest in combining a little cow manure with prickly pear type cactus fermented in a drum for a period of time. The gelatinous goo is mixed in with the plaster at about a quart per wheelbarrow. We are still looking for a good dome plaster ourselves. We will have to replaster two this spring. For a culture that is used to frequent maintenance that is acceptable but for the Modern American Ethic, long term solutions are the sought after ideal. Short of standard stucco systems on a good moisture/vapor barrier we still don't have that figured out. Let us know how it works out.

Q: I wasn't clear if compressed earth block requirements would be exactly the same, according to the codes, as adobe.

A: Some soils that will make adobes will not work for CEB's and vice versa. CEB's are made pretty dry so emulsified asphalt cannot be used as a stabilizer.

Q: Can either tung on linseed oil be used for strengthening an abode oven given the temperatures as high as 750 degrees?

A: We have not tried tung nor linseed oil on adobe ovens so I don't know if it will work. We have found that just plain natural adobes work fine and on some occasions we have used asphalt stabilized adobes. If asphalt stabilization works then my guess is that linseed or tung oil would work. But that is a guess. Good old nothing always seems the best bet unless you are in a mood to experiment and report back with your findings. Over many years of use we do see that some of the interior surface of the ovens flakes off. Never enough to compromise the structure however. Most ovens collapse from exterior water problems.

Q: I am a 32 year old single mother of 2, who got 15 acres awarded to me from the divorce. With little money but lots of enthusiasm and determination, I have laid the footings for the adobe block and now have reached some bumps on the road. My next step was to lay the adobe block but now I can't find anyone with an adobe machine. I'm leaning more towards making them myself, or purchasing them in Mexico 5 miles away. Enlighten me, please any suggestions would help. I have plenty of land and great soil for the adobes.

A: You are just the type of person for whom adobe was created. You can certainly make adobe bricks yourself. A form that makes 4 at once uses the contents of a standard wheelbarrow. In New Mexico the standard adobe size has somehow turned out to be 10x14x4inches. The 4-inches can be 3-1/2" if standard lumber is used to make a form. One of my women students is happily making adobes for herself. It is hard but rewarding work.

You can certainly buy adobes in Mexico. Sometimes they are stabilized with asphalt but in Mexico it may be "cut-asphalt" which has some solvent in it which can give residual out gassing. Try to get natural adobes or adobes stabilized with emulsified asphalt which will not out gas.

In the long run, you may be happier with sun-cured bricks you have made yourself or purchased. The machine made bricks are a little different to lay up. With regular adobes you can place UF electrical cable in the mortar joints to run electrical outlets around your rooms. You can do plumbing by chipping adobes to fit around pipes and tubing.

Around the border, there are often many people who associate adobe with tough economic times. They think of adobes as simple huts. Far from it, the adobe home is the most powerful construction presently practiced on earth - not counting the new concrete and steel filled foam form things - which will suffer the fate of Hummers and regional airports as the fuel cost squeeze hits the construction industry. In New Mexico all the MacMansions are adobe or fake adobe. It is recognized here as the premium building material. You will be proud of yourself one day soon.

Q: I've sampled my dirt and did that test in the water bottle. I'm not sure I did it correctly because I have half water and half dirt. No layering of sand, rock or anything. What does this mean?

A: Many times the jar test does not show clear layering. That may mean that you only have one constituent, sand, silt, clay or humus. Or it could mean that the gradations are so close that you cannot see a line of demarcation. Add a pinch of salt, shake it and see if it changes. All the scientific tests end up saying that you should make some test bricks just to be sure. You can skip it all and just make test bricks. If they crack, they have too much clay and need sand, sometimes lots of it. If they don't seem strong, they may need more clay until they begin to crack. Maybe you can find some viejitos around who have actually made adobes and they can give you some hints.

Q: My husband and I are making a small structure from adobe bricks. We've found the mixing to be the most difficult part - particularly when there are lumps of clay in the soil - and have heard a lot of conflicting advice about using cement mixers. I would be interested in hearing your thoughts around the best type of mixer to use for adobe.

A: A cement mixer works just fine unless there is too much clay in the mix. In that case the mixture just goes around with the drum and does not mix. With the addition of sand, the mix will begin to fall off the blades and back to the bottom just as concrete does.

Lumps are a problem for sure. Sometimes the best approach is to pile the dirt up and carve out a depression at the top and fill that with water. Let it soak and that will loosen up the lumps, usually. Myself and instructor Anselmo Jaramillo have come to the conclusion that mixing can be avoided by just plain soaking in a pit and then shoveling the mud into a wheelbarrow and poured into a brick form or shoveled onto the wall as mortar.

Q: I am wondering if I could use carpet waste mulched or shredded as a full or part replacement for straw in adobe, cob or mudbrick application?

A: That might work. No one I know has done it so you will be blazing new trails. Certain fibers yield adobes with increased compressibility and modulus of rupture. I don't think there is any way to predict how carpet fibers might work.

Q: I teach a high school architectural drafting program. In this program I include Elements of Construction and Intro to Engineering in my program. I am very interested in starting a renewable resource portion and Adobe building really strikes my interest. We are located in Ganado Arizona on the Navajo Reservation about 70 miles north-northeast of Holbrook Arizona. Could you give me some information on where to purchase an Adobe Block press and possibly a good strong Adobe Block recipe?

A: There is now a page on adobe in Francis D. K. Ching's Building Construction Illustrated. The best book is P.G. McHenry's Adobe Build It Yourself from the University of Arizona Press. I don't know of anyone manufacturing hand presses in this country at the moment. The old standby, the CinvaRam, can sometimes be found on eBay or Craig's list. We have an old one here at Northern New Mexico College and you might consider bringing students over for a day to try it out. You can always make a wood form and cast adobe bricks to sun cure on the ground. In the long run, it is just as fast or slow as the CinvaRam since the pressed adobes are at most half the size of the 10x14x4-inch New Mexico adobes or the 8x16x4 Arizona adobes. A good recipe for the mix is 30% clay and 70% sand. Any more clay and the bricks begin to crack. Straw will help control cracking. Too much sand has little effect on the strength but the bricks are less water resistant.

Q: I am currently working in Indonesia for my own organization Smart shelter Foundation, where we have started our new adventure with adobe. We are now on Bali, which has a risk of moderate to heavy earthquakes. That is the reason why I want to make the strongest possible blocks we can. We have soil here that is extremely clayey, around 80 to 85%. So we need to mix in a lot of sand. We can also include rice husk as a fiber. We have made some samples so far, and 1 soil : 1 sand : 1 rice husk had good results; not too much shrinking and not so much cracking. What I am afraid of, is the cost of the blocks because sand is expensive. Also I am not sure how much termites will like the rice husk.

Here's my questions: What will theoretically give the best block, a block with only soil and sand, or a block with soil, sand and rice husk? Is fiber always necessary, or can adding the right amount of sand sufficiently prevent a block from cracking? Which block will become better or harder: a sun-dried block or a block dried in the shade? What would be an ideal block size for an earthquake region, 300x300 mm or must it be bigger, up to 400x400 mm? Do you have any experience with rice husk being attacked by termites? Have you ever heard of treating fiber or rice husk with borax? What could be the effect of using such chemicals on a block? Do you know of any simple field tests for determination of the compression or bending strength? How much stronger would a cement stabilized block be, if we keep the rest of the mixture the same, especially in an earthquake prone and monsoon prone area?

A: I commend your efforts. Yes indeed the 30/70 clay/sand adobe brick is the best for strength. Higher clay decreased compressive strengh but the bricks are still useable if they do not crack too much. The cure for cracking is fiber or sand. I have no experience with rice husks/hulls so have no idea how attractive they would be to termites. We live in an area here that is lucky to have few termites. Somewhere in your area there should be sand and it might be down a few feet below the serface of the ground. If you can locate sand, then by all means pursue that course. Silt contributes nothing to an adobe brick. It has no cohesive power as does clay and it has no strength as does sand and larger aggregates.

Borates are about as safe a chemical as can be found so adding it to adobe with rice hulls should pose no toxic risk. But it is one more ingredient that has to be acquired. It is commonly used in cellulose insulation in the US.

A common size adobe in New Mexico is 250x350x100mm. Just how it developed is unclear but it does allow us to build walls that are either 250 or 350mm thick which just happens to be minimum code required wall thicknesses for one and two story construction.

If you build walls that are a minimum of 250mm thick and don't go over 2500mm in height you will have met the first requirement for strong walls. A good foundation and a good bond beam at the top of the wall will tie the building together and spread the roof load while providing a good anchorage for the roof. A properly built roof then provides a diaphragn which further stabilizes the building. A good foundation, bond beam and roof diaphragm are more important than the strength of the individual bricks.

There are many opinions regarding earthen construction. That is because given a bit of time to experiment, nearly every method and material source can be made to work. Half the planet's population can't be wrong. The fewer ingredients involved, the more likely a local population will accept adobe construction. If people have to go looking for rice hulls, borates, lime, cement or even clay the more likely they are to be discouraged.

Q: We are planning to build an adobe home on our farm in Montrose, CO. The soils on our farm are "expansive clay", meaning that there is not a single concrete pad in the county which has not buckled (unless it was poured in the last decade using post-tension concrete, which we will use for out pad). For purposes of making block and mortar, would this type of soil be suitable, assuming introduction of aggregate, which currently is non-existent, or is its chemical composition different? An elderly neighbor told me there once was an adobe block plant in town, although I am not aware of any adobe buildings (perhaps they all blossomed and washed away).

A: There was a man in Montrose who had built five houses. He wanted to do one of adobe with my help on design and consulting before he died. Cancer got him before he realized his dream. About 1986. I have lost his contact information but he might have set up the adobe yard. There was another in Canon City perhaps Compressed Earth Block. Another in Pueblo West. Montrose does have a nice college with some pv collectors on the roofs. Sweet retirement center where Uncle Raymond lived out his years. If the soil is expansive then it will be hard to make bricks that do not shrink and crack too much. If they can be made, then they will be especially vulnerable to getting damp. There is always another source of good clay a few feet down or a mile away.  Aggregate is always good for adobe bricks and particles up to 1/3 the thickness of the brick can be tolerated. Adding course sand almost always makes a stronger brick. A couple of little communities around Montrose have Spanish names. That is usually a hint that there will be some historical adobe to be found in the area. Remember the San Luis Valley which exists due to adobe. It was the double adobe walls with air spaces that formed the potato sheds with dirt - now call green or living - roofs that allowed the farmers to store their potatoes at no energy costs until market conditions brought the best price. There might even be some adobe barns or sheds around Montrose. Best barns ever. Adobes did not wash away. I just sent off a long note on how adobe structures in Hatch and Albuquerque, NM hold up to three day floods better than frame houses. At four days, it gets messy.

Q: In an adobe mix can you add more than straw, clay, soil and water? How well would Adobe Bricks work if you added shredded paper?

A: Lots of folks make adobe bricks with just clay and sand. If the soil has the right blend of clay and sand then it can work as is. Straw helps minimize the cracking that occurs in bricks that are too high in clay content. Cracking can also be controlled by adding sand. Straw is lighter so if it works it saves hauling sand. Straw also helps adobe bricks stand up better if the form is removed immediately to make the next brick. Some folks just make a lot of forms and let the bricks dry out for a few hours or a day. Shredded paper might work and I am sure that it has been tried. No one has reported back so I have no information.

Q: I am interested in building an horno but I don't have access to a location where I can dig up the dirt I would need. If I mix 3 parts of dry powdered fire clay with seven parts of sand would that give me the consistency I need for the adobe?

A: That should work perfect.

Q: I am a Florida teacher that attended a histori

ly.cal seminar in Santa Fe this summer. I figured it would be easy to find a adobe brick souvenir to bring back to show my students. It wasn't. How can I get 1 adobe brick that shows the straw in it for my classroom?

A: Somewhere in the Florida high country there is a streak of clay. 30% clay mixed with 70% sand will make a perfect adobe brick. I am sure that sand can be found somewhere in the state. Straw is not absolutely required and the idea that it is necessary can lead to situations such as that faced by Moses who could be controlled by Pharaoh's withholding straw. Straw is useful to keep bricks with a high clay content from cracking as they dry. That should not be a problem you face. If you really want straw, there are those cattle ranches rumored to exist in Florida. There might be farm stores in the rural areas which would have a few straw bales on hand.

Then, you and your students can mix up some mud and place it in a wooden form that is an open rectangular wood box 10-inches wide, 14-inches long and 3-1/2 or 4-inches high. The form can be made of 1 x 4's or 2 x 4's with perhaps some help from a parent.

You can work outside on the ground or if rain is expected within a week there might be a dirt or concrete surface under a roof but hopefully arranged so that some sunlight hits the surface. Once a brick is cast, lift off the form and if the mud is stiff enough the brick can just sit there on the ground and dry out. In the ensuing bedlam of enthusiasm on the part of your students just keep going and make a brick for everyone. In about a week you will have (an) adobe(s) brick(s). Don't stop there. Build something.

It is not necessary to work at the full scale as above. Miniature bricks can be made at any size in smaller forms. Florida has a history of tabby construction that is similar to adobe. Tabby uses crushed shells and sand, I think. There may have actually been a few adobe structures built by those near clay deposits. Your students might be surprised to learn that there are 2,000,000 earthen structures (adobe, rammed earth, cob, wattle and daub, and compressed earth bricks) in Central Germany.

An adobe brick weighs about 30 pounds. It will be so much easier to make one than to talk UPS into shipping it.

Q: I'm always using the right proportion when making adobes (Mud and straw), however, I am curious if anyone is utilizing volcanic ash. The latter one when mixed with water becomes very hard, I don't know if the volcanic ash chemical composition allows mud to adhere well. I would appreciate your guidance.

A: The best adobe bricks, mortar and plaster result from 30% clay and 70% sand. Silt and other materials are often found in soil and add no value to the strength of the material and sometimes decrease it. Straw is one way to keep bricks of higher clay content to keep from cracking when they dry out. In the 30/70 brick they add no strength but in lower clay ratios straw might add some strength in the ability of the brick to hold together and that might be seen in tests of compression and modulus of rupture. In the case of volcanic ash, I have no experience in its use. I am not aware of any studies of incorporating it into adobe bricks.

Cement has been widely used in adobe bricks. Most studies conclude that cement and clay are not compatible and that the first part of cement added to adobe is consumed in neutralizing the cohesive abilities of the clay and that the balance of the cement added then provides the adhesive strength for the brick. Therefore, to get successful soil/cement bricks it is necessary to test each soil to be used to determine the percentage of cement that will be required.

So, if you have a source of volcanic ash, I suggest you make test bricks using 3%, 5%, 10%, 15%, 20%, 25%, 30%, 35% ash by volume. Without laboratory equipment available you can simply drop bricks from knee height on hard soil or concrete surfaces. Bricks that survive the drop test have been found to be roughly equivalent to 300psi compressive and 50psi modulus of rupture. Those are the minimum requirements for strength for the New Mexico Earthen Building Materials Code and several other codes found worldwide.

Q: We live in Placitas, NM and have interior exposed Adobe walls. My dogs (who are getting old) have decided to start eating the surface corners of the walls. I would be so grateful if you have an adobe patch solution which I could use to build back up the corners and smooth out without it crumbling all over.

A: Well, this is a new situation for me. I have not heard of dogs with a taste for adobe. Most of the Placitas area is automatic adobe. If the dirt out your back door will not make perfect adobe bricks, mortar and plaster, then certainly a blend of arroyo sand and most any other dirt with a bit more clay will make a good mix. I don't know Placitas well enough to give specific locations but a couple of years ago, I stopped to look at the new fire station and there were some piles of dirt that looked perfect. Whatever you use, it should be screened with about a 1/8 hardware cloth as if to make plaster. Then it can be troweled on to the adobe bricks and tooled with a trowel, spatula, spoon to re-create the shape of the bricks. The best patching material for adobe bricks and mud plaster is the same material as the original. If there is an original brick lying around, it can be ground up to make the repair. A person with experience or one willing to experiment could use a gypsum based plaster such as Red Top with three parts sand and then once it cures color it to match with a kit of water based paints. There might be an old-timer in the neighborhood to whom this sort of thing seems routine. I guess you need a dog whisperer to change their habits.

Q: I am working on a latrine project in Africa. I would like to make the structure out of 'Adobe' bricks but the most plentiful raw material seems to be termite mounds. Do you have any recommendation about how I might go about using the termite 'soil' as raw material for an 'adobe" brick?

A: Africa is a vast space and I have never been there yet. Many of the termite and ant soils that I have read about make perfect adobe bricks. If the material will mix with water, place it in a wood form and then it will dry in the sun into good hard bricks. I don't know enough about termites but some species add chemicals to their soil that might make it harder to mix with water. That's good for the termites and the longevity of their structures but not for the people who need to mix it with water. Here in New Mexico I have been known to harvest as much as I can of the material that ants bring to the surface. It makes perfect bricks but I don't get a lot of volume.

Q: I used to live in Northern Chihuahua, and Southern New Mexico, where I fell in love with adobe. I now live in Delta, Ut, which is located in the Great Basin. The elevation is about 4500 ft, we get about 9 in. of water a year, the soil is salty clay and the winters are freezing, windy, long, and just harsh in general. However, I want to pass this long winter building adobes from a hole that will be my future root cellar. How do I build adobes and turn them into a room above the root cellar in the dead of winter?

A: Add water to clay based soil, mix it up and form it into a brick with a wood or metal form then let it dry. In warm, sunny, breezy weather it takes about five days or a week to dry enough to handle. In three to four weeks the brick is dry enough to build with. That is the adobe brick making process.

With the winter conditions at your location, cover the hole with clear plastic - perhaps a very economical greenhouse kit that provides the greatest amount of floor area possible. It will be much slower than in the summer but if the greenhouse or plastic cover can prevent freezing, you can make adobe bricks. If you cannot protect them from freezing then you are doomed. Doomed that is, to wait until April 5 when heavy freezing will not take place in the Great Basin of Utah. You could always provide a source of heat but that would not be adobe. Adobe gets the energy it needs to evaporate the water content from the sun.

First experiment with seven bricks that you can protect somewhere to see if the salt content of the clay might be a problem. Certain salts in certain concentrations can prevent the ability of clay to bond particles. If all is well, thirty percent clay is what makes a good brick. Any more and the bricks will crack but that can often be minimized by the addition of straw. Any less clay content clear down to 6 or 7 percent will still make a strong enough brick but it will have reduced resistance to moisture.

There are many historical adobe homes south of you at Georgetown. I don't have any information about Delta and its surrounding area but in general, if you are far from timber supplies, early settlers would have turned to adobe if salt content of the soil was not a factor.

High speed adobe construction consists of speed leads which outline the outside corners of a building. Strings are then run from the speed leads to keep coursework plumb and level. So, build very sturdy speed leads now and use them with perhaps some intermediary wood members to support clear plastic. Now you have an enclosed space in which to make adobe bricks. In the spring, take off the plastic, run the strings and replace the plastic with adobe walls.

Q: What are stabilized adobes?

A: Unstabilized adobes or natural adobes are just dirt, water and perhaps straw. Stabilized adobes are those that have sufficient stabilizer - emulsified asphalt, lime, cement, polymers, catalysts, green cow manure - to pick up no more than 4% moisture when placed on a water saturated surface for one week. This code requirement is a functional requirement, not a stated amount since different stabilizers in different soils act differently. In practice, it is often achieved with 24-ounces of asphalt per wheelbarrow (4CF.) Semi-stabilized adobes have enough asphalt to protect the bricks from rain while they cure on the ground. I don't fool with lime or cement so I have no idea how or why in this era of green materials they are used. Stabilized or semi-stabilized might be good in a humid climate. Interior walls can and should be unstabilized.  Some people are uneasy at the thought of asphalt in the walls which is then in contact with the air in the structure.

Q: I am building an adobe house in Baja California south of Ensenada. I want purchase emulsified asphalt to stabilize the adobes. I am having trouble finding this. Do you know of a place in Baja or in Southern Cal where I can purchase it? Is emulsified asphalt a liquid or is it goopy and needs to be heated?

A: In NM we buy emulsified asphalt from a small supply company that sells to driveway resurfacing businesses. They have it is 5-gallon buckets. It is definitely a liquid and will mix readily with water which is the source of the "emulsified" nomenclature. Mexicans also produce and use similar products but sometimes it has a more oily (as in diesel) smell. USA e/a is odorless once mixed into floors, mortar, bricks or plaster as long as you do not overdo it. About 500ml per wheelbarrow of mud is the upper limit. It can also be brushed, rolled or sprayed onto the top of a foundation to stop upward migration of water into adobe walls.

Q: I am doing some archeological work analyzing some historic adobes in Big bend National Park. One of the questions we have is how to identify adobe stabilized with asphalt emulsion.

A: Emulsified asphalt's presence in bricks, mortar, plaster or floors can be detected by breaking up some material in a wheelbarrow filled with water. Non stabilized materials will dissolve straight away. Emulsified asphalt materials will sink into the water but particles the size of sand or dust will skitter along the surface of the water. I am sure there is a scientific explanation for this but I have lost little sleep over it. I will settle for something messing with the surface tension. At a higher level of precision, chunks of fully stabilized material will still be chunks after three or more weeks. Semi-stabilized chunks after three weeks will be mud or very mushy chunks. Non-stabilized chunks will have lost all shape and will have turned to nice mud ready for its next incarnation in two hours to two days.

Q: The plan is to make the adobe from dirt plus horse or burro poop.   Do you know if the poop is a good substitute for clay?

A: The value of horse and burro poop is the shredded straw that their chewing provides. Fibers will not make adobe stronger but it will prevent cracking when the clay content is too high. I have seen no improvement when clay content is low. I don't think there are any chemicals in horse/burro poop that will provide strength or adhesive abilities. Australians feel that cow poop harvested green from the field and cured a couple of days in a barrel will improve cohesiveness. The demonstration they did on a building at Pojoaque Pueblo twenty years ago did not persuade me of the value of following cows around a field. Other folks, notably Simone Swan of the Adobe Alliance in Presidio Texas, have fooled with aged, fermented prickly pear cactus. The prickly part keeps me at a distance. It is mighty gooey but they use if for plaster. It would require a vast amount for making bricks. Adding clay does not take a large amount of material so I think finding a source of clay is the easiest route to good bricks.

Q: I've read that the ancient Babylonians knew how to "waterproof" adobe brick, but the art was lost for centuries, until the last 50 years or so when people began using emulsified asphalt to make water-resistant bricks. Has anyone discovered exactly how the ancient Babylonians did waterproof their adobe brick?

A: That's a really good question and I don't know the answer. Early peoples on various parts of the planet had access to bituminous materials but whether or not they would mix with water and soil, I don't know but ancient peoples were very clever in using what they had at hand. The modern emulsification magic began with Phillips 66 in Oklahoma or Chevron in Southern California depending on who tells the story. The smartest thing the Babylonians did was to locate their city in a dry, arid region so that erosion from rain would not be great. Perhaps there would have been rising damp from the ground if the water table was high enough due to the location between the Tigris and Euphrates rivers.

Q: I have adobe bricks (real adobe bricks) that I want to dissolve in water so I can use the mud to replaster areas of my adobe house. I have trouble getting them to dissolve in water. What should I do? How to crush them?

A: Normal adobe bricks dissolve readily in water. The mud makes great plaster, mortar, floors or new bricks. By normal, I mean natural or unstabilized. There is a good chance that your bricks were stabilized with emulsified asphalt, cement, lime or some secret formula. If you fill a wheelbarrow with water and whack the bricks with a hammer, at least some particles will be knocked off. If they just skitter around on the surface of the water in defiance of what would be expected then you probably have asphalt stabilized bricks. My experience is that cement and lime stabilizers do not produce this effect. In any case, bricks with stabilizers do not recycle nearly as well as natural adobes, if at all. Once cured, the asphalt molecules are electrically bonded to the clay molecules and cement molecules are chemically bonded to the sand particles. There are soil grinders at sand and gravel companies and they might agree to grind up your bricks. However, you would need to add more asphalt or more cement to once again bond the clay or sand. But you might be lucky. Go back to that wheelbarrow and fill it with bricks. Then cover them with water and hope the wheelbarrow does not leak. In a day or three, the bricks might turn to mud of their own volition. I have some bricks in my yard that came from an old house ten miles up the canyon and they take several days to melt. Some natural soils make bricks that are surprisingly water resistant. If the bricks are stabilized, it is time to think about acquiring new soil and starting from scratch.

Q: I built an adobe courtyard wall last summer, with much help from Quentin's advice, but never quite got around to finishing it off. I build it from semi-stabilized adobe with the plan to do a mud plaster and then lime wash to protect it. It is starting to deteriorate. I am thinking about lime washing right over the bricks rather than putting on mud plaster first, as I like the look of the bricks. But before I get to that, I tried this week to round over the top of the wall using mud mortar. I used fully stabilized mortar (20 oz. asphalt per gallon of water) and the mortar substrate I bought from from the supplier of my bricks. The round overs looked great...until a few hours later large cracks perpendicular to wall appeared and also it was apparent the new round overs were not adhering to the top bricks in the wall (I could easily pry them off the next day). I tried again adding a shovel full of horse manure to the mix, with same result. So my questions are: What can I add to the adobe mix to prevent the cracking and get the mud to adhere to the top layer of bricks? Do I need to make the round over thicker (they way I tried it, it was 2 inches thick in the middle tapering down to to no thickness at the outside) and should I reduce the asphalt to better match the semi-stabilized adobe bricks? Any other additives to help?

A: The dirt you got for mortar from your adobe supplier should have worked perfectly. I don't have a great answer other than when there is cracking it is usually an indication of too much clay. The remedy for that is to add sand. Also, I don't understand why it would not adhere better to the top of the adobe wall. Asphalt usually makes it a bit more sticky. Maybe it's drying too quickly in the sun and heat. I have used Franklin or Elmers waterproof glues in small patches of adobe plaster to adobe walls and that seems to work. But that was on vertical surfaces. My mix was 12 to 16 ounces per wheelbarrow.

It certainly has been hot so I am sure that is a factor. I found that if I went back as the cracks were forming but before the mud was fully dry, I could press the cracks together and that worked or repair the cracks afterwards. Also I am hoping the lime wash will seal some of the microcracks on the surface.

Q: I know that organic fibers are used in making adobe bricks. I wonder if long bamboo fibers would work well? Has anyone tried it?

A: I am sure someone, somewhere, at some time has tried it. My thought is that the longer the fiber, the better. Nripal Adhikary of Nepal has done lots of work to incorporate bamboo into earthen structures but more on the order of a replacement for reinforcing bars. Mel Medina at the Adobe Factory in Alcalde, NM did discover that barley straw makes adobe bricks stronger.

Q: I have just put an offer on a half acre lot in New Mexico where I want to build my own adobe house. Before I close the sale, is there anything else I should look into on the site itself to make sure that it will be feasible both for me to make my own bricks and to build my house? (I don't plan on making a huge house ... 1000 square feet-ish). Is it reasonable to expect that I will be able to bring in either sand or clay if the composition of the soil isn't just right, or should I have the soil tested as well before I close on the sale? I suspect that the soil is more likely to be too high in sand than too high in clay, but not sure I can tell. It is a light color, and I notice that it is very soft when I walk on it. Not hard packed.

For a thousand squarish feet you will need around 4000 bricks if your interior walls are adobe and I certainly recommend that. A half acre is around 20,000 square feet and you can easily lay down 10,000 adobes with a little pre-planning. After two days you can pick up the adobes on edge and clean off the bottoms. After a week they are cured enough to move to pallets or to stack off to the side. Two people with a wheelbarrow, a pile of loose dirt that is the proper blend, a water source, and a form that makes four bricks at a time have been known to make 250 adobes per day. 100 per day might be more realistic in the beginning and then with experience and stamina building the number can be moved up or prudence may dictate making fewer.

Many soils in New Mexico are automatic adobe material. Rarely is there too little clay. More often there is too much clay and the bricks will crack as they dry out. It's easy to call in a truckload of sand from a nearby sand and gravel operation. I prefer plaster sand over concrete sand. The grains are more uniform and larger. It's not so easy to call in a load of clay since it's a by-product or actually a waste product at most sand and gravel operations. At my favorite supplier, I myself would go down and look over the "trash" piles since I could easily judge those heavy in clay. The suppliers don't concern themselves with clay percentages since it is not normally a salable product. On the other hand you might find a supplier who deals with other adobe builders and therefore has a sense of which piles work for bricks. In the end, even the most technical systems to analyze soils for bricks end up with the statement "make some test bricks to verify your blend." So, just start making test bricks.

Get yourself a copy of P.G. McHenry's book, Adobe, Build it Yourself, University of Arizona Press, $27.00. Then you will fear nothing. With today's prices on lumber and building materials, the cost of an owner-built adobe home will look attractive by comparison.