Debarking and Curing Cordwood
Rob Roy is Director of the Earthwood Building School, which has specialized in cordwood masonry instruction since 1980. Rob and his wife, Jaki, have built four innovative cordwood homes for themselves since 1975, including the Earthwood home where they have lived for over three decades. Earthwood is a 2400 SF two-story round, load-bearing cordwood home, earth-bermed and earth-roofed. Details of construction are in Rob's Earth-Sheltered Houses (New Society, 2006) and Cordwood Building: The State of the Art (New Society, 2003) two of fourteen books he is written in the alternative building field. Rob and Jaki have taught cordwood masonry in Earthwood Building School all over North America, as well as in Chile, New Zealand, Australia and Hawaii. They have helped scores of owner-builders with their cordwood projects, including homes, saunas and outbuildings. Earthwood has produced a 3.25-hour DVD on cordwood construction, which, with his books, can be accessed through the Earthwood website, or on the Cordwood page here. Rob is considered to be one of the leaders in the field of cordwood construction and earth sheltering. He does individual consultations at a flat rate of $75/hour, but answers questions here without charge. See also Earthwood Facebook.
Questions and Answers
Q: I am in a difficult situation and need a small piece of wisdom. I am hoping to build a small shelter this spring/summer out of necessity - long story - and I just sent you an order for your Stoneview book. I'd like to get a Stoneview-like cottage up this summer but I have no cordwood yet. What would be the dangers/problems of building with green cordwood? The house we were building was to be strawbale and after attending your Timber Framing for the Rest of Us class last summer I was inspired. This building, my temporary shelter, will eventually be used as a studio/guesthouse. Any advice would be greatly appreciated!
A: Stoneview is built with 8" log-ends, so they dry pretty quickly. Get your wood cut into log-end length right away and stacked in single ranks, off the ground (such as on pallets). Do not place one rank of wood up against the other. On pallets, put a rank at each edge of a row of pallets, with about two feet of space between ranks. Cover the tops of the ranks, but not the sides. Let the sun and wind get to the wood, plenty of ventilation. With 8" log-ends, a lot of drying will take place in a short period of time. Tip: for stability of piles, put a 4-foot long "sticker" (stick) to tie the two ranks together, every 3 feet or so. Goes a long ways towards stopping the stacks from falling over. (Eight-inch wide stacks are inherently unstable.)
It will take you time to do the foundation and the framework. The wood can be drying all this time. And a lot of it will get additional drying while you lay up the first panels. Hopefully, you will not have a major shrinkage problem. But if you do: There are log chinking products which will close up shrinkage gaps of a quarter inch or more, and they are flexible, so that if there is any further expansion or contraction of the wood, the product will move with it. Two good ones are Log Jam by Sashco Industries and Perma Chink by Perma Chink Corporation. Get the 5-gallon pails, not the 32-ounce caulking tubes, much cheaper. Apply the product to the mortar joints, thin as possible, making sure that all shrinkage cracks are filled. Do not do this until at least a year has passed. the products are expensive and you don't want to do this more than once. Apply it with a pointing knife, but draw it out with a water-dampened 3/4" paint brush.
If only a few large log-ends shrink, just get a couple of tubes of clear siliconized caulking and caulk the shrinkage gaps. Clear caulking shows less than white or gray.
Q: I live about an hour west of Edmonton, Alberta, and plan on using the local poplar as cordwood for our home. I was wondering what would be the most efficient way to debark the trees without using an expensive machine. I was also wondering if you knew what month is the best to catch the sap up in the tree. I am having trouble finding information about the growth pattern of what I believe to be "Quaking Aspen" in this area.
A: You are right to try to bark the quaking aspen while the sap is rising in the spring. The sap rises between the wood and the bark, in a layer of soft cellular tissue called the cambium, forming a greasy lubricating layer and making bark removal a satisfying joy. When the sap is not present, or has dried, the effect is that the bark is "glued" onto the cambium layer, which, in turn, is connected to the outer wooden layers. That's when draw-knifing or powered barking tools, such as the Log Wizard come into play. The Log Wizard, incidentally, is a chainsaw attachment made by Goldec International Equipment of Red Deer, Alberta, not far from you.
Local woodcutters should be able to advise you as to when sap normally rises in your area. Of course, normal seasonal variations (and maybe global warming) can change this by a month or so, just as maple season (sap rising) can vary by a few weeks where I live in the east. The good news is that you have a window of opportunity of a couple of months or more. So the best advice I can give you as this: Cut one of your quaking aspens on April 1st (no fooling) and, right away, try barking it with a sharp-pointed tool such as the pointy end of a strong mason's trowel. You should be able to get the tip of the trowel under the bark easily, and work it back and forth a little, until you can get your hand in there and pull wholesale (8 to 10-foot) strips off the log.
It is important to get right on the barking job right after the tree hits the ground and you've cut it into convenient 8-foot to 10-foot logs. After even a week, the sap begins to stiffen and act as a glue instead of a lubricant, and you have lost your advantage. If it is difficult to get the bark off, wait two weeks and try again. And again. And again. I don't know when sap rises near Edmonton, and it can vary from year to year, so keep trying. A week of warm weather should give you a good clue.
Q: If we cut the aspen this winter and peel it, will mid spring ( May/June) be an appropriate amount of drying time for the wood? I am thinking that I will gather about 10 bush cords this fall to set out till then.
A: It could be difficult to peel wood cut in winter, but is worth a try. You do not indicate the length of log-ends that you will be using. This impacts drying time considerably, as does splitting the wood. Therefore, it is difficult to answer your question as to whether or not using the wood in May or June is "appropriate drying time." Even with the answers (length of log-end, split or round), I would be guessing. You will probably get some wood shrinkage, but if you really need to build, then build. You can attend to the wood shrinkage down the line. Is a "bush cord" the same as a "face cord," defined as an 4' by 8' rank of wood cut at some particular log length?
Q: We anticipate cutting the wood over the next month. This is still warm enough to work outside comfortably. The sap is still high in the trees. We want to build the double wall version with each wall being 10 inches thick.From a log splitting perspective, we will try and keep the logs ends round, but I anticipate anything over 12 inches through the center will be split in two. Not as appealing to some, but still usable above the doors and windows if placed decoratively, we think. The plan is to harvest wood from 12 inches down to about 5 inches. The leftover wood will make excellent starting kindling for the hearth.
A Bush cord is 8 feet by 8 feet by 4 feet. A Face cord is 8 feet by 4 feet by 16 inches. One thing that you mentioned in our last correspondence was the laying out of the logs in order to avoid the fungus that attaches to drying aspen. It seems to create a punk wood, sponginess that obviously makes it unsuitable for this project. Can you re-explain the correct way to dry it and thus avoid this scenario?
A: Yes, bark the wood, then cut it into your 10" lengths. Stack these "log-ends" in single ranks, covering the tops, but not the sides. Old metal roofing makes a good cover. As 10" log-ends are somewhat unstable, you may want to stack two ranks on a pallet, with 3 feet between them, and tie the ranks together with frequent 4 foot long one or two-inch stickers.
Q: We own 40 acres in central Arkansas, and we have had our property "select cut" in order to thin out our forest. This was done in March and April. We have many treetops left on our property that we have been cutting up for firewood. My question is this: can we use this wood that has been on the ground exposed to the elements for building a cordwood home? If so, do we need to get it cut and out of the elements right away? If not, is it best to use fresh cut trees? We still have 40 acres of forest in which we can cut fresh trees, so either way will be fine.
A: If the wood was cut in March and April, I doubt if it would have deteriorated by now. It is unfortunate that you didn't get the bark off when it was first cut, as it could be quite a bit more difficult to get the bark off now. See other postings or my book about barking the wood.
You do not mention the species of wood you have, so please look through the other Q's and A's in this column. And you can use wood right down to two to three inches in diameter. These are very handy in the masonry process.
Finally, if you find any deterioration in the wood, such as "punkiness," don't use it. But if there is just a slight deterioration on the underside, you can easily split it off when it is at log-end length.
Q: I have seen where you think cottonwood may be a good source for saunas. I have an abundant supply here in Southeast Alaska. Will I need to dry them until seasoned or can I use them shortly after being cut down?
A: Yes, I like cottonwood as a choice for log-end material. Although technically a hardwood, in that it is deciduous, it performs more like a light and airy softwood (unless your Alaskan cottonwood is radically different from the ones I've seen in the lower 48.) In other words, it is fairly stable with regard to expansion and contraction.
I would dry it as long as your time schedule will allow, but no need to go over a year in any case. You could build with it soon after cutting it down, as you suggest, but you can expect a certain amount of wood shrinkage in that case, Even a couple of months of good air-drying will make a huge difference, especially as you only need to go about 9 or 10 inches thick with the walls for your sauna, and cottonwood will dry rapidly on end grain at that length. I have always built eight-inch (8") walls in the cordwood saunas we have done, but we have always used white cedar, with its higher R-value.
Q: I'm planning on doing some cordwood masonry. Is it important to get all of the cambium layer off? The bark comes off but we are going back over logs to remove extra cambium, I was wondering if this is necessary. Also, is there a way to tell if a tree is hollow before you cut it down? We have cut down some nice looking poplars that were hollow inside.
A: Part one first. No, it is better to leave the cambium, which is just a microscopic layer between the wood and the inner bark. Better not to cut into the wood, just get the bark off. When the sap is rising, it forms a nice greasy layer between the cambium and the bark, making the bark easy to remove.
Part two. No, I don't know of any way to tell if the tree is hollow before cutting it. But, with cordwood masonry, I have never thought of this as a big issue. In fact, one of the plusses of cordwood is that you can use wood which is unsuitable for the sawmill or for other purposes. If there is just a small hole in the center, stuff it with insulation and put mortar at each end, about three inches deep. With larger holes, we center a smaller log-end or a bottle-end inside it, pack the gap with insulation, and, again, insert mortar about three inches deep. Some of our most beautiful log-ends are hollow.
Q: I am trying to find out if I need to take cedar that is 5-7 years bone dry and wet it a little so that it doesn't expand.
A: It is a guessing game to try to pre-swell the wood to prevent expansion. How long does it continue to swell? I tried something like this 30 years ago with very dry hardwood without success. With white cedar, you should not have a problem with wood expansion, even though it is dry. Keep it away from the ground and use a good overhang. Split or sawn log-ends, especially down low in the wall, would greatly benefit from a single application of Silicone Magic or equal ( a siliconized waterseal) or other clear water seal. These products cut out almost all of the transfer of moisture from the mortar to the very dry wood, greatly reducing the likelihood of wood expansion.
Q: If I cut some Juniper by December in Wisconsin, would it dry enough to be laid in a cordwood structure by mid-March? It would dry in the basement of a barn.
A: I'm afraid that you can expect some considerable shrinkage on your juniper under the conditions and time frame you describe. I would think you would be only slightly better off if you air-dried it off the ground (pallets are good) in single ranks with a cover over the top, such as old metal roofing. Even then, after a year of curing and shrinking in place, you would probably have to apply a product to the mortar joints like Permachink's log chinking or Log Jam from Sashco Industries.
Q: My current concern is with my wood that is drying in two 12'x20' portable shed garages. The gable ends are off and they seem to be drying fine, it's just when the snow melts the dew comes through the roof and makes everything in there very moist. My plans were to keep it under cover this way for the fall rains, winter and spring rains, and then move it out for more sun & wind exposure. Do you see great problems with this?
A: Get your cordwood out in the open as early as possible. Keep it off the ground on pallets. Stack it in single ranks. Cover the tops of the ranks (perhaps with old metal roofing or equivalent), but not the sides.
Q: A neighbor/handyman friend built his own log cabin in the 70s here. He said he started out with cordwood but had a problem with the gaps created from the mortar with logs shrinking, so he tore it out. This sounds like a major problem and entryway for insects and cold. Can you comment?
A: Back in the 70s, before there was much readily available info on cordwood, a lot of people - including Christian Bruyere who wrote Country Comforts - made uneducated decisions with regard to selection of wood species and drying times. Going back even further, people in Canada (and Wisconsin) ended up covering their cordwood walls when shrinkage became unacceptable. They used plaster, and even clapboard siding.
Jaki and I have built around 16 buildings for ourselves and lots of others for friends and workshop hosts. We are careful about the wood we use and have never encountered a problem that required entire wall treatment. We have had a few very large log-end (used for special features) shrink in the wall and they have been quite easy fix with one of several methods developed over the years, and discussed in my books and on the Q and A pages.
Q: I was once told to cut cedar down in fall and debark them. Is it the wrong or right time to do it?
A: Here in the north, I do not hesitate to recommend cutting the trees in the spring when the sap is rising. For us, in New York, this can be anytime from the end of March through June. The advantage is that the rising sap creates a nice greasy layer between the bark and the cambrian layer of the wood, making it easy to get the bark off. Just insert any pointed tool - I like a regular pointed mason's trowel - and get the tip under the bark. Then it is possible to pull wholesale strips off of the long log. It goes real fast without damaging the cambrian layer. 50" and 100" lengths are good cutting length choices for rough logs to haul out of the woods. The shorter 50" pieces might be necessary with heavy (large diameter) logs. These lengths work well with 8", 12", 16" and 24" log-ends: you can trim the ends and you still have enough extra to take care of the several 1/4" kerf spaces that you lose with chainsaw cutting. Practically no waste.
But southern Missouri? I don't know. I imagine that the sap rises and falls with the seasons, there, too, which leads me towards cutting and barking in February or March. There is no harm in trying one or two now - late November as I write - and see how it goes. If the bark is sticking to the wood like it is glued on, wait three months and try again. In any case, cut your long logs into short log-ends right after you bark them, and stack them properly in single ranks with a cover over the top (not the sides!) Wood dries about ten times faster through end-grain than through side-grain.
Comment: If the logs are too dry when installed and prone to expansion upon wetting, the swelling logs can crush and damage the mortar, which creates potentially serious structural issues.
Response: Swelling wood can cause structural damage, as Jaki and I well know, but it is not from crushing mortar. The expansion causes an uplifting on horizontal members much like frost heaving. On round structures, the effect is to tilt the walls outward.
Comment: The general approach to dealing with this issue is to repeatedly caulk the cracks and seal the log ends with any number of commercial caulk and sealant products.
Response: If the builder waits a year after construction, after the structure has been heated, one repair with clear caulking is generally sufficient. We have had very little such "repair" at Earthwood.
Q: I'm putting up a quick cordwood auxiliary building add on/ tool shed, and am wondering if I can get by not peeling the bark. It seems like easy to peel wood has termites, and robust wood I can't easily get the bark off this time of year. If I get 10 years out of it or less, that's ok.
A: The main reason that we take the bark off the wood is that, eventually, the log-end will shrink away from the bark anyway, leaving an attractive place for bugs to get in. You mentioned that you have termites, but there are other beetles and the like that just love these natural gaps, too. The only two woods I have used successfully with the bark still on have been lodgepole pine in Colorado and linden (basswood), here in New York. In both cases, the hard woody bark was like an extension of the wood's outer cambium layer. For the purposes you describe, and your hope of getting a few years out of it, then I would say. "Go ahead and build with the bark on." Maybe, after a year or two, you can improve on any shrinkage by the application of a few tubes of clear siliconized caulk.
Q: I have someone coming out today to take down several 40' poplars & just realized that I should be peeling them and saving to build a cordwood barn! BUT, I am not prepared for the peeling and not sure what to do. If I have him buck them into 8' lengths and leave them where they lay, how long do I have before it will be next to impossible to peel them?
A: By "poplar," I am assuming that you are referring to quaking (or trembling) aspen, not tulip poplar or Lombardy poplar. This is the best time of year (March) to bark quaking aspen (most woods, for that matter.) Get any sharp tool between the bark and the cambium layer and take advantage of that nice greasy layer of rising sap to help get the bark off easily. I actually use a pointed mason's trowel. Get the point under the bark and pull off wholesale strips of bark. Eight-foot lengths are a good choice, but even better, is 100 inches (8'4"). At that length, you can later cut the log into 12 log-ends at 8 inches, 8 at 12 inches, 6 at 16 inches, 4 at 24 inches, and still have enough log to trim the ends and allow for the several quarter-inch kerf cuts made by the chain saw. For easy handling with really heavy logs, cut them into 50-inch pieces, which have the same numerical advantage. You want to get onto the freshly cut 100-inch pieces as soon as possible after they are cut from the tree, preferably within 48 hours. After a while, the nice greasy sap layer that makes it so easy to get the bark off turns into a kind of glue, sticking the bark to the wood. Now the barking process is very much more difficult. After a couple of weeks, especially in dry conditions, they might, indeed, be "next to impossible to peel them" easily. A lot of rain - or storing the logs in a pond - will extend working time.
Q: I have seen conflicting opinions on curing/drying/fumigating the cordwood before building with it. I have plans to use dried seasoned cordwood, but I have been bombarded with other peoples concern over putting the cordwood into a storage container and fumigating it first... which goes against my original principle to do no harm to the environment.
A: In my view, fumigating is unnecessary.
Q: We will be building a 24x38 cordwood home in western Virginia. We have cut and peeled a number of white pine logs for the walls and they are currently stacked with spacers. How long should we leave them stacked to dry before cutting to cordwood length of 16"?
A: Cut them to their 16" log-end lengths now, or as soon as possible. The only log-ends doing any significant drying right now are the ones at the ends of your long logs, and very few inches in at that. Wood dries ten times faster through end-grain than through side-grain.
