Miscellaneous Questions about Lightweight Concrete

Fernando Martinez Lewels has a M.S.C.E degree from the University of Texas at El Paso. He is now working with the Agartif company in Chihuahua, Mexico (about 170 miles from El Paso Texas). This Company has developed a type of lightweight aggregate that provides material for all types of construction needs, at reasonable cost and with good thermal insulation values. They manufacture the equipment required to do this according to the needs of their customers; the feed stock are common construction materials that should be available in most locations. Their philosophy in developing this type of aggregate is to be able to use this everywhere, without depending on a lightweight aggregate quarry, so you can have access to this material in any part of the world. In Mexico we have a saying that "we build our homes so we have to go outside in the summer to be fresh, and in the winter we go outside to catch the rays of sun to be warm". Lightweight concrete can help this situation by making available materials for more comfortable homes.

Questions and Answers

Q: Where can I get the pumice aggregate to mix my concrete in the West Virginia area?

A: (Kelly) Such volcanic rock is more common in the western states, but you might check with landscape supply companies, as this material is sometimes used for landscaping.

Q: My only hesitation in using pumicecrete is using the inert material of concrete. So, I was wondering if I could replace the concrete with an earthen mixture in 18" thick walls?

A: The pumicecrete works well because it uses a minimum of cement to bind the pumice or scoria into a solid mass. If you used soil to bind the wall together, it would loose much of its insulating value. Rammed earth walls can be created without stabilizing with cement, if there is the right amount of clay in the soil mix, but again rammed earth walls are not well-insulated, although they can work well in fairly moderate climates.

Q: I was interested in making concrete fence posts for some property I own. I've gotten instructions on how to do this using regular concrete from an old USDA bulletin (circa 1937). The posts are said to weigh over 100 lbs. apiece however. Is there any lighter weight concrete available that would suit this purpose?

A: (Kelly)You could use a lighter weight aggregate (such as scoria, perlite or vermiculite) for your concrete, but these materials would compromise the ultimate strength of the post...I would stick with concrete as the posts will stand up better over time.

Q: Where can I buy cinders. I want to manufacture my own special blocks. My location is WA State north of Seattle.

A: (Kelly)You might check with local landscape supply yards...they often carry a variety of crushed volcanic cinders for decorative landscaping.

Q: Could you help me find a manufacturer of lightweight foaming agent and not a middle man, same goes for a small foam generator. It seems that some of these companies are trying to get rich or something. Needing a direct foaming agent maker.

A: (Bruce) In terms of "foaming agents" or air entrainment, you might want to go to our web site where we have a number of them listed at http://www.schundler.com/air&pumps.htm .

Q: Do you know of anyone using hempcrete in India? I am involved in a community project in north India, in a densely populated area designated as being at high risk of earthquakes, where hemp grows as a weed beside the road, but where most buildings are of brick bonded with mud, on 3 foot foundations. We are trying to find building techniques and materials that could be adopted by local people to build homes capable of withstanding earthquakes and/or built of materials which are less likely to crush people when they fall down. We thought at first of straw bale building; but the 2ft thick walls would be impractical in an area where space is at a premium. So now I am seeking information/advice about hempcrete.

A (Kelly): I have heard of the use of hempcrete, particularly in Canada I believe. Unfortunately it is illegal to grow hemp in the US, so there is little experimentation with it. I know that hemp is an especially strong and durable fiber, so there should be ways to utilize it, perhaps pressed into fiber boards which could be the skin of SIPs (structural insulated panels). I encourage you to experiment with the possibilities.

Q: We are just completing exterior construction on a scoria home here in Carefree AZ. I'm not a builder but we hired one many months ago to complete the scoria part of the construction. Now that we've completed the exterior, we have turned our attention to the finishes that would be best for the scoria walls. We were under the impression that one could plaster directly on the walls without any further prep. Are we correct or can you advise the appropriate way to complete the interior?? Also, we are intending to stucco the outside with typical Western 1 Kote stucco any problems with adherence etc?? The walls are 12" thick.

A (Kelly): The rough pumicecrete wall is a perfect substrate for the application of conventional plasters and stuccos, or natural earthen or lime plasters as well.

Q: I have a severe case of MCS (multiple chemical sensitivity) and find it hard to live in most buildings. I have been thinking about building my own from straw-filled concrete. Something like papercrete only using straw.

A: (Kelly) I have heard of using straw as reinforcement in concrete instead of steel mesh. There have been some experiments with this in Canada.

I have also thought about vermiculite but it is very expensive. We are very poor. I want to build it on a reinforced concrete platform, like those used for elevated parking garage platforms with an open "first floor" with just laundry room workshop and utility room; the rest would be open with columns. This would be to avoid moisture, mold and gases from reeking up into the first floor. I have often thought this would make an excellent template for building in New Orleans flood zones, with the first floor above the flood line.

The concept of building above potential flooding is certainly a good one. I am afraid that concrete with a substantial amount of straw in it might not be strong enough to span the distances required by such a structure. Those parking garages are carefully engineered with pre-stressed steel reinforcing embedded in the concrete.

 I  thought that straw concrete would be lighter and easier to work (I have back problems) easier to drill through, and lighter too, making the platform sturdier.

Again, while such a concrete mix might be lighter, it would not likely be as strong as ordinary concrete.

I am also worried about the insulation and building code problems I may encounter. I am presently thinking about buying land in the Cambria-San Luis Obispo area of California.

You are talking about earthquake country here, so I am sure that you would run into some pretty stringent code requirements for building, and your straw/concrete idea may not sit too well with the authorities. Also, although such straw/concrete may be more insulating than standard concrete, it will not likely be very insulating.

 Please tell me of any information and publications that would be useful.

If you go to the "lightweight concrete" page, there are links to more information about this. Perhaps a combination of ordinary concrete for the platform base, with lightweight concrete for the walls would work.

Today I ordered a book on papercrete for starters. I am a little worried about outgassing from inks and chemicals in paper of unknown origin, which is why I thought of straw instead. Would that be a problem?

Papercrete is similar to "lightweight concrete" in some ways, but it must be very carefully used, because it is much more absorbing of moisture, which can easily lead to mold problems. With your environmental sensitivities, I suggest that you steer clear of of this particular material. I don't think papercrete outgasses much, once it is cured, though.

From Michael Collins: This is a hybrid structure using fishingnet, latex, pumicecement, and fibercrete There are more pictures on ferrocement.com. The arc is where theVirgin of Guadelupe sits on her feast day. It is now acid washed and looking more finished.

(Owen): Aircrete is growing extremely fast. Numerous companies are investing in it. This means aircrete tools, supplies and materials will soon be more widely available.

(Kelly): I have very mixed feelings about the technology. It obviously has the potential to fairly easily create durable, insulated shells, but this is at the expense of a considerable amount of Portland cement with its foaming agent and equipment to mix and transport it. In other words it is not inherently very green to my mind. They say you can make about 50 gallons of the stuff with one bag of cement. Well, that adds up to about 9 standard earthbags full.  A building that uses 1000 bags would be using 111 sacks of cement... ugh! I would rather promote natural materials.

(Chris): I do like aircrete with relevant mix ratios, and allied surfactant foam. I use it on sculptural ferrocement roof sections. Something like 70% of new construction in Germany is aircrete, typically either precast panels (walls,floors,roof, everything) or jumbo blocks with 1/16" mastic joints. Awesome stuff. Even aircrete slabs, and under the road stabilizing pours.

Q: I would like to learn how to make my own "Airkrete" I believe Airkrete insulation would encase & protect the wood studs against moisture & insects, thus I wouldn't need to demolish an existing buildong & re-build using metal studs.

A: (Chris) Structural aircrete isn't insultive. Insulative aircrete isn't structural. Insulative aircrete in very low densities and psi such as Airkrete TM company (search YouTube) isn't easily DIY'ed, as it is high tech to make stable. This is easy to figure out in smaller lifts like I use sparingly on ferrocement roofs in order to flatten out a surface for rigid foam. Any real lifts like cavity fill will be difficult to DIY. As a side note, higher densities approaching 'Structural aircrete' is easier to DIY, but is obviously more risky if load bearing.

I highly prefer top shelf surfactants (such as Allied) for superior bubble stability, hydration catalysts (PMT), some fly ash or other cheap pozzolan, and definitely superplasticizers--just in case you wanna play with weird cements. I'm not saying that you can't get your cavities stuffed with aircrete by following online DIY recipes and mixing with the dome Gaia dragon etc. I'm just saying that it's highly unlikely with basic surfactants, mixes, aerators, mixes, pumps.

Note: AirKrete company, I believe, has the best product with regards to shrinkage. You get what you pay for with cavity blown aircrete. Also, depending on where your electric and plumbing is run, you may want to be sure that they are good to go before you decide to encase them in aircrete. Even if they are good condition, calcium rich materials like lime, setting/hot gypsums, and Portland cement eat away PVC and cpvc. Romex, NM, UF electric cables are sheathed in PVC thermoplastics.

Comment from Owen Geiger: Interesting video on  Formless Vertical Concrete (SpaceCrete). www.youtube.com/watch?v=_NYAv2sMm1c This is a clever system with lots of potential. Instead of Portland cement, you could use magnesium cement or other type of geopolymer. Use expanded clay and/or expanded recycled glass or scoria to boost R-value, plus add a pozzolan such as fly ash or rice hull ash. This would create a green, rot proof, lightweight, insulating building material that's affordable, efficient and goes up quickly.

Q: I want to build a rocket stove with perlite and aircrete. Can you suggest the correct ratio of Portland cement, perlite, water and foam. My foam is 95 grams per quart. I am pouring around my rocket stove in a 31 gallon trash can.

A: (Chris Steen) Aircrete isn't suited to the extreme temperatures of rocket stove combustion chambers or heat risers. Nor would any lightweight mix be durable enough for the burn chamber. Mixing waterglass into the mix or completely submerging the casting could help. But any real durability is found with traditional materials (high temp firing clays). Check out the book and the donkey pro forums, as they have done all the research and testing already.

If you are looking to keep the trash can as a permanent container and no steel or aircrete actually see any temperatures, then I suggest you make test mixes. Light enough to move around if you want. But dense enough that it would not crumble if you want to move it. If you are not planning on moving it just pour loose perlite/vermiculite or pour straight up lightweight aircrete. A lot depends on the surfactant and mixing processes. I suggest you make test samples and pour and set in lifts if you go real lightweight so that you don't collapse your matrix. I don't see advantages in mixing aircrete and cinders. If you want to move this regularly, a denser mix will be more durable.