Q:   What type of soil is best for use below grade?

A: Using the soil at the site would be ideal, and most any type can work, but it should be relatively free of organic material and large rocks; it is best to avoid heavy clay soil.

Q: I have been trying hard to surf the various web sites so as to get any idea about the width of earthbag wall or the recommended dimensions of the bags for this application. Would you please give me any idea on this request.

A: The earthbags that I have used are designated as 50 pound rice bags, and are about 17 inches wide when flat and 32 inches long. This size works well, but is not critical; the bags could be somewhat larger or smaller, but I wouldn't go much smaller or the stability of the wall might be questionable. Larger bags would be more stable, but take more material to fill them.

Q: Kelly used volcanic rock material to fill his bags - I don't think that's available in the UK. Is there an alternative - or is the answer just earth?

A: Most earthbag building has been done with earth from the site, or I've heard of crushed shells being used. The advantage of the scoria is its insulative properties, and light weight. If enough insulation were used on the outside to insulate the structure, then dirt might make a comfortable dwelling in extreme climates.

Q: My wife and I plan on building next spring and we are searching for a source for scoria or pumice in Michigan. Most, if not all, sources are limited to landscape suppliers and cannot supply a large volume. What is the going price per ton or cubic yard in the west?

A: The source for scoria where I live is Colorado Lava. Their number is 800 528 2765 and the going rate seems to be around $16.00 a ton plus delivery charges. The mine is just outside Antonito, Colorado, on the New Mexico side of the border with their main offices in Illinois.

Q: I live in Arizona, where is a good place to purchase earthbags for the super adobe buildings?

A: I've been getting them as misprinted 50# rice bags, in bales of 1,000 from Inpack, at 800-622-3695. They can UPS them.

Q: If bag builders use earth with a little cement to harden it - do they mix it in with a spade into a large pile of earth or somehow mix it in for each bagful?

A: I haven't done this, but I imagine mixing it in a large pile, or even with a cement mixer would work.

Q: I've had to clear grass and foliage from my land to open the building site and the soil is full of stones, roots, weeds, seeds and bluebell bulbs! Should all the dirt be sifted before packing into the bags to prevent things growing?

A: The less organic material used the better. I let some small roots go into the bags at times. I wouldn't worry too much about things growing there because moisture and light will not be available when you are finished.

Q: What about worms and insects in the bag dirt?!

A: I would think that eventually it would not be a hospitable environment for them, and they would die.

Q: Are these materials resistant to fire and insects?

A: Most earthbag buildings are completely fire and insect proof. Mine is covered with papercrete, which is fire resistant, but which will smolder if it gets hot enough. To mitigate against this, I put a lot of sand in the final coat of papercrete on our house, which makes it much more fire resistant.

Q: How does one seal a filled earthbag?

A: The answer to this question is actually not so simple, since various methods have been used, under various circumstances. The most frequent method that I have used is to simply leave enough exposed bag at the top to allow that extra material to be folded over when the bag is laid horizontally. The weight of the material in the bag will provide the seal, even with very fine sand. I usually laid this folded end of the bag against the previously laid bag, so that the loose end has the additional support of the other bag to lean against.

Occasionally, I will need the full length of the bag for some reason, such as when I am creating an arch with two bags side by side covered by two more bags lying at right angles to the first ones. In this instance the top of the bag will need to be sewn or stapled closed, so as not to spill its contents. Sewing a double-folded hem with heavy nylon thread is the strongest method, but this is sometimes overkill if there is not much inherent pressure on the hem. I have lately been simply stapling the folded hem with common office staples, especially if the entire assemblage will subsequently be covered with a plaster that will protect the seam.

Q: Your work looks so neat - presumably there are times when the full bags don't quite fit in a row and you have to use half a bag full?

A: I often used partial bags.

Q: Kelly used plastic? twine to anchor the bags as well as barbed wire - is it vital? I was also a little confused about how many levels were lashed together?

A:The polypropylene twine is not essential, but it does help with the stability while building, and more importantly, it gives the eventual plaster material something to grab onto and lock into place. The twine circled three bags, so each bag was lashed both upward and downward.

Q: I think I would prefer walls that 'solidify' during the tamping process. I saw this kind at the Cal-Earth institute and liked them. They make me feel safer about the redundancy of the bag as only a temporary form. My question is, if I build during the winter, (Gallup/Zuni New Mexico with freezing nights and milder days) will I have a problem with the earth setting up during tamping? Does the slightly moist mixture need some 'curing time' which would be interfered with by the freezing temps at night?

A: Cal-Earth does what they call "Super adobe", which is basically common adobe soil (30% clay, 70% sand) that has been dampened. As this dries out it hardens into a very solid material. If the damp soil freezes, it can expand and fracture, so it becomes less solid. So if you used this method, you might want to throw some blankets or something over the wall at night to keep this from happening.

Q: We have started building our earthbag house.. and it is going surprisingly fast. We're nearly half way up the walls and love it already. We are building on reclaimed TIFF mines and using the "leftover's" from the mining operation to fill the bags which is a mixture of small sharp rock, sand, and red clay. It compacts very well and the walls aren't budging. The clay retains water for a long time and there has been a lot of press about mold lately, I am wondering if we should give some time to let the walls dry out before covering with stucco?

A: Soil rarely harbors mold; usually you need a more porous and organic medium to support mold. On the other hand, you don't want to trap moisture within the wall for very long either. My suggestion is to either allow the soil in the bags to dry out thoroughly, or plaster them with something that will breath enough for the walls to dry our over time. I advocate breathable walls anyway, as this is generally more healthy for both the building and the inhabitants.

Q: Do earthbags settle? If I support the roof partially on earthbags and partially with poles will that cause problems due to the bags settling?

A: It really depends on the type of material the bags are filled with, and how well they are tamped. Some of our bags are filled with sand (which basically does not settle) and some are filled with scoria (crushed volcanic rock), which has settled slightly. Had I tamped the bags more thoroughly as I was building they would likely have settled even less.

Q: Do you have more info on how high you built with loose sand?

A: Yeah, on our first experimental dome we tried using the sand on our lot, since we are basically living on a big sand dune. It is a very fine, sugary sand that is spherical rather than sharply angular. I think that is the problem, because it just doesn't pack into a solid shape and stay there. It is more inclined to do what sand naturally does: shape shift.

Q: At what point did the corbel fail?

A: We got to just about door height before it fell.

Q: How did it fail? Slipping? Or deformation of sand in bags?

A: Deformation of the sand in the bags.

Q: Just cave in quickly? or?

A: I was working up on the wall when I noticed that the perimeter shape at the top had become a little lopsided...there was a straight section where it should have been curved. At that point I thought "This wall could fall in!", and I jumped off to the outside. Then I watched as the wall slowly collapsed, like in slow motion. Sort of like watching dominoes knock each other over. It was beautiful in a way, but also very depressing. The fact that I had tied all of the bags together with twine, as well as use the barbed wire, may have contributed to the whole thing falling in, because once it started to fall, it acted like a continuous fabric. Actually, the wall up to about 2 or 3 feet was fine, and I left it in place. Up to that height, the wall was nearly vertical, so it was not inclined to fall.

Q: If we use a concrete/sand mixture can we use paper feed bags instead of the poly? It seems that the poly bags with that type of mixture are just to hold the form until it dries- is this assumption correct? If I am right about this then wouldn't it be the same idea using unlined paper feed bags? These are much cheaper, about $160 per thousand, and have a wet load tolerance of 50 lbs.

A: You are right that with filling the bags with either dampened adobe soil or a concrete/sand mixture, the bags only hold the material in place until it sets up. However, I would have a couple of concerns about using paper bags for this purpose. Will they hold up well enough when damp? A 50 lbs tolerance may not be sufficient for the perhaps 100 lbs of material they would be filled with. The polypropylene bags that I used were misprinted rice bags, which cost me about $190/thousand and they are extremely strong and durable if kept out of the sunlight.

Q: Can you give me an idea about the labor on vertical walls (e.g., maybe an approximation of a certain length of wall, say 9' high per person...)?

A: Building with earthbags can go surprisingly quickly. Here is an example: I just facilitated a workshop on various aspects of sustainability for an international conference held in my home town. My particular portion of this was to coordinate about a dozen people at a time building a sort of earthbag gazebo and amphitheater. We were filling the bags with the local sandy soil dug right on the site. We only worked about 3 hours each day for a total of five days, which works out to about 180 person-hours to complete the building of the walls. The total surface area was about 700 square feet...so one person at this rate could create about 4 square feet. Of course these were complete novices at the process and they were also clearing the land, digging and transporting the soil, and doing a lot of standing around and talking. This rate could easily be doubled or tripled under different circumstances. When I was building my house, I used to lay 2 or 3 courses around a perimeter of about 75 feet in one day. This works out to about 14 square feet per hour. I was filling the bags from a nearby pile of scoria (crushed volcanic rock). I hope this gives you some idea of how fast it might go.

Q: I have begun to build a 30X20 studio, with a basement 11X12. I was not able to find the scoria that you use so am having to use blue gravel, 3/4" crushed and it is very heavy! I could sure use some help, my body is complaining loudly.

A: The crushed volcanic rock (scoria) is certainly easier to work with than ordinary gravel would be; a bag of it only weighs about 35 pounds. It is also better insulation because of all the trapped air in the rock. Regular gravel will probably give you some insulation, for the same reason, but probably not as much.

The scoria also packs into something that becomes fairly solid, which your gravel may or may not do. If it is crushed, and not smooth, then it will likely pack pretty well. This could become an issue if there is any tendency for the bags to move or roll once they are in place in the wall; some gravels have a tendency to do this.

Q: Is it possible to do earthbag construction using waste rock (gravel) from quarries or any other type of waste?

A: I used crushed volcanic rock to build my house, and I know of another house that was built with bags filled with crushed shells from the beach. As far as other waste material, whatever goes in the bags should be inert and dense enough to not compress much when stacked up, so most mineral material fits this description.

Q: What will happen to the structure when the bags rot after some time? I am afraid that when the bags are worn out or rot then the remaining earth structure will no longer have strength to hold on together and will be vulnerable to damage due to rain, wind, excessive sun (long period of drought).

A: The answer to your question depends on what material the bags are made of, and what they are filled with. If the bags are filled with a moist adobe soil, or stabilized soil, then it doesn't really matter if the bags rot, because the structure will remain solid. If the bags are filled with a looser material, then you should use polypropylene bags rather that burlap or jute, because it will not rot over time. You do need to be careful to keep the sunlight off the bags as much as possible and plaster them with something to protect them from the UV in the sun.

Q: I heard that you created a way to build to allow a larger opening. Please explain.

A: I did devise a way of interlacing pairs of bags over an arch form to span 6 feet, which enabled me to create some large openings for passive solar gain.

Q: Can you tell me more about this interlacing of bags to increase the possibility of a larger opening?

A: Yes, the basic pattern is like this photo, where two bags are placed side by side, and then the next course of two bags goes at right angles to the first, then the courses alternate orientation as they are stacked. This pattern can create more stable columns than single bags, and they can be stacked over arch forms to make the arches. It is not necessary to angle the bags over the arch; just place them horizontally and corbel the bags to create the arch. In order to get the bags to fit this way I had to fill them very full and staple or hem the bags so that each bag was twice its width.

Q: I'm planning a sculpture studio in southern Illinois, and I'm going to use post and beam construction with a steel arch roof. I have a 20' grid that I'm working on, and the exterior dim. is 40' x 80'. With each bag at 35 Lbs. and measuring about 14" x 20" full, I figure I need 384 full bags for the 20 'wide x 16' height that each exterior wall requires. That is assuming that each bag is only 6" thick when filled. Is this correct?

A: A full bag does measure about 6" high, so each bag would fill about .83 sq. ft. of wall area, and your calculation of 384 bags for that wall is about right.

Q: I want to build with earth. Earthbag construction seems to be the simplest way. Should I have the earth I am going to use excavated now (putting a pond where the earth was) or dig it out as I use it. What is faster and more efficient?

A: This probably depends on several factors. The closer the soil is to the project, the easier and faster it should go. Soil is heavy stuff, so the less you have to lift and move it the better. In fact, as the walls go higher it is often easier to carry buckets of soil to fill the bags in place, rather than heft them up from the ground, especially if you are working alone. So it might be easier to excavate the soil first and have it dumped nearby. Also some soils are difficult to dig, so having a machine do some of this work could save your back.

Q: Is it better to use a single long tube method of construction (Nader Khalili) or single bag at a time. Which would be faster for one person to do?

A: I am not much of a fan of the long tubes. I find them a nuisance to fill, they can only be filled in place, and they have a tendency to roll. Especially with one person, I would recommend using the individual bags.

Q: I read about the admirable properties and low cost of rice hulls, a waste product apparently available for purchase (+/- $6.00 per ton) at rice mills in a number of states. High in mineral content, the husks are a good insulating material and relatively fireproof. Such a material sounds like a good possibility for filling bags to make an 'earthbag' shelter, except that the rice hulls would be lightweight, possibly easier to handle for anyone with limited assistance in building their home, or building in an area where they do not want to disturb the ground in order to obtain earth to fill the bags. Is there any reason you can think of why such an alternate filling for the bags would be a poor idea?

A: I would think that under certain circumstances earthbags could be filled with rice hulls, and that this would create a very insulated wall, since there would be a lot of air space around the hulls. You might not want to use these bags in a situation where they would be load-bearing, because they might compress too much, but as infill in a post and beam structure they should work fine.

Q: I am considering building a small earthbag home and have been reviewing what lightweight aggregates are inexpensively available in my area. It occurred to me that the "bottom ash" produced in coal combustion furnaces would probably make a good lightweight aggregate and provide some insulation value. I later found that it has been used experimentally to add insulation to rammed earth structures. Any thoughts about using this material to fill earthbags? I was thinking of a double-walled structure with the outside walls made of bottom ash filled bags and the interior walls made of native soil or trucked-in sand for nice thermal mass.

A: This sounds like a good idea to me. I am not totally familiar with the "bottom ash" that you describe, but it could be an excellent insulating building material, especially if it is lightweight (full of air pockets). Doing a double wall with this on the outside and soil on the inside should provide an extremely comfortable, energy-efficient home.

Q: Does securing the bags with courses of barbed wire really give them enough strength to not need load-bearing beams?

A: The barbed wire is used for two reasons: to help stick the bags together and form a matrix within the wall system, and also to resist any tendency for the wall to expand from weight from above (in domes), so in this instance the wire would help with load-bearing capacity.

Q: What are the chances of filling the bags with sea sand?

A: I would say that it depends on where they will be placed (vertical walls are usually not a problem) and how "packable" the sand is (does it hold its shape when packed into a bag, or does it slide around?) Some experimenting may in order to determine how well it will work.

Q: I live in northern Vermont and am very interested in building a round, yurt like home with earthbags. With the need for insulation & some mass - in your opinion, how would lightclay (wood chips & clay) work as a supporting wall?

A: I suspect that this would hold up quite well, especially if you created a solid wooden or concrete bond beam at the top for the roof to sit on. Also you might let it all settle awhile before plastering (making sure to keep the sun off of the bags.)

Q: Is it better to not make courses so perfectly level; add in small sine wave and more like seashells, which would make structures considerably stronger as then sides come up with strong ridges.

A: This might be true, although if you use the barbed wire between the courses they need to be relatively level and uniform in order for the wire to be effective as a bond beam. I have found that the wire adds considerably to the strength of the construction.

Q: Concerning earthbags, can they be filled with 'woodchip'. I have plenty of woodchips from some pine trees that we had to remove. How would 'peat' work? Living in Ireland, we have plenty of peat and I understand that it has loose particles. This should help its ability to hold onto heat?

A: You certainly can fill earthbags with almost anything, including woodchips and peat. The efficacy of doing this depends on how you intend to use the bags. Neither woodchips nor peat would be able to withstand much pressure from weight, so you would expect some deformation over time, which could be disastrous in some circumstances. On the other hand, if the bags were not expected to hold much weight (such as when they are placed in a roof cavity), then they might be quite useful to insulate that area. Both woodchips and peat are subject to rot if they are moist, so that is another concern that should be addressed.

Q: Several articles regarding building with earth say the first 2-3 rows should be gravel to allow for water to drain down. Since gravel is unstable this seems like a bad idea.

A: If you are referring to earthbag construction, then the gravel-filled bags are actually plenty stable, since the bags hold the gravel intact, and so does the eventual plaster.

Q: I have purchased bags to begin a small home for my son and me. The bags are 14x21 and 16x31. 1000 of each. I am now worried the smaller bags will be of little use. Is it possible to use these for earthbag building, possibly alternating rows?

A: The larger bags are better for insulation and stability. I wouldn't advise staggering the rows, as it is better to have a solid base for all of the courses. You might consider using the smaller bags near the top of your walls, or for interior partitions or something, if necessary.

Q: Does it matter that burlap/hessian bags rot if you intend to cover exposed surfaces in cob or lime plaster and that the bags will be filled with mostly clay sub soil when building an earth bag structure?

A: In this case, it probably doesn't matter, as long as the earthen material is kept absolutely dry so that potential deformation of the wall is not an issue.

Q: I would like to use existing site material, a heavy clay, without amendment. Is this feasible?

A: If you use heavy clay like this, the real danger is that it might expand if it gets wet, or contract if it gets dry, so the challenge would be to keep it from taking on water. You wouldn't want to fill the bags with damp clay, since it would shrink as it dries, or it could provide moisture problems if it is left damp. I would only use dry clay in situations where you were absolutely sure that it would remain dry. Ideally you would only want about 30% clay to 70% sandier soil.

Q: To speed up the earth bag tamping process do you know of anyone who has successfully used a small powered plate tamper (as opposed to the Pogo stick variety)? Apart from the safe physical handling of the machine would there be any disadvantages?

A: I don't see why you couldn't successfully use a power tamper, although for the sort of earthbag work that I have done this would be overkill, since the loose volcanic gravel and the sand that I used to build my house don't need that much compaction. For adobe soil compaction, then I think such a power tamper could actually save quite a bit of work.

Q: I am curious if you know if the long sandbag tubing that CalEarth uses is more structurally sound than the large rice bags. Are there any benefits to one over the other? Disadvantages?

A: The long tube bags that CalEarth typically uses have both advantages and disadvantages. Their use does reduce the number of seams between individual bags, and for this reason might contribute to greater stability of a wall. To my mind, this is about the only advantage. I find them much more cumbersome to actually fill and place on a wall, and they practically demand that at least two people are involved in the process. A major problem that I encountered was that they tend to roll as a unit when filled with loose material, like the crushed volcanic rock that I used in my bags. This is not so much of a problem when they are filled with adobe soil like CalEarth uses. Individual bags have a seam at the bottom, which gives each bag a distinct orientation that tends to keep it from rolling this way.

Q: "Vermiculite" as a viable product for insulation of your green home. Vermiculite or "Asbestos" as it is better known, is a well documented product for its cause of lung cancer and silicosis-like effect on tissues. I would hope that you would mention these particular warnings to anyone that might use the "Vermiculite" idea from your page.

A: Thank you for alerting me to this potential problem with vermiculite, which I was not aware of. In doing some on-line research into the question, I have discovered that pure vermiculite does not contain asbestos, but that there was a period of time when asbestos contaminated vermiculite mined in Libby, Montana did contain some asbestos. This contaminated vermiculite found its way into some residential insulation products sold up to about 1996 in the U.S. and Canada. If disturbed, this insulation can become a health hazard if the dust is breathed. That mine in Libby has been closed down for several years and is no longer producing this contaminated vermiculite. Current sources of vermiculite are carefully monitored for this potential problem, especially because of the alert that has been issued by the U.S. EPA. It is my understanding that unless you go digging in someone's attic to obtain the old contaminated vermiculite, there is little danger in using newly available vermiculite.

Q: I have available barbed wire that is two point. Will this work if I use two strands? And can I wind the wire over and under each bag rather than keeping the wire in a single line between courses for added integrity?

A: Two-point barbed wire will work...it just isn't as good in gripping the bags as four-point would be. In either case I recommend using two parallel strands, at least 6" apart. As for weaving the wire, doing this would not be a particularly good idea, since it could actually diminish the integrity; the wire needs to be able to act under tension to resist outward expansion of the wall from the pressures placed on it from above. Also interweaving the wire between courses would make it difficult to get adjacent bags to make good contact.

Q: Do we REALLY have to diddle the bags as shown in Doni and Kaki's book?  It seems a smack with a hammer and thick earth plaster will cover them.  Don't want to create any extra work.

A: Diddling is one of those areas where Doni and Kaki reveal their fascination for perceived perfection. I have never diddled a bag, and simply give the point a bang with the hammer before plastering. If the bags you use happen to be pleated, even this is unnecessary.

Q: I see that you used local sand to build the Glorieta project. My son and I are planning a similar project, our site soil is sandy as well. Were you moistening the sand in those bags or just tamping the dry sand? Has there been any structural failure due to the sand shifting?

A: We just filled the bags with the dry sand; I don't think moistening it would have made any difference since it is a rather fine and slippery sand. Had there been any clay to speak of in the soil, moistening it may have been effective in getting it to solidify some. Since the structure had perfectly vertical walls there was no problem with the bags wanting to shift, and once they got covered with chicken wire and stucco the structure has been quite stable.

Q: I have just bought some land in Lexington, Oklahoma ... and I am planning all that I want to do and how I want to build... and I need to know where can I get scoria?

A: Scoria is a type of volcanic stone that is often available in regions where old volcanic activity has occurred. I don't know whether it is available in your area. It can often be purchased at landscape supply outlets, since it is commonly used for landscaping, but it may be quite expensive if purchased far away from the natural sources.

Q: Is it possible/recommended to use earthbag construction for interior walls?

A: You can certainly use earthbags for interior walls, but bear in mind that they do take up that extra space, and that if there is going to be much plumbing in the wall it is often easier to use conventional wood framing.

Q: I have sand where I want to build a project. If one was to use Portland cement with sand, what ratio of mixture would you suggest?

A: You could probably sufficiently stabilize sand with a ratio of about 15:1 sand to cement; although some experimentation is advised. Ordinary concrete can be made with about 9:1.

Q: Do you have any idea where we can find rice hulls in the NY area?

A: I'm not sure about finding rice hulls in NY. Mainly these are available where they do the processing of rice, which is generally in the southern states I believe, like Texas and Florida. It might take some Googling to find a source close to where you are.

Q: We live on the Big Island of Hawaii and need to build a quick structure about 400-600 sq' We are thinking that Earthbag building is the way to go. We have cinder available to us as filler for the bags. Do you think it would be wise to also mix in cement?

A: I used a kind of cinder (scoria) to fill the bags for my dome home, and it worked great...wonderful insulation. This was 3/4" minus gravel, without much dust in it. Larger aggregate might not work as well. I did not use cement, and I don't think it is is necessary.

Q: Could you please tell me which kind of polypropylene bags are more suitable for soil cement: a) the ones that are kind of porous (such as those for rice or corn) or b) the ones that  are kind of impervious (such as those for flour or sugar)?

A: I would vote for the more porous ones, because they will allow any damp material to dry our better.

Q: Here is a sketch of a thought of mine about building with earthbags. Would you mind giving me your thoughts on this?

A: This is certainly an interesting idea, and a great drawing! I think that I understand your concept pretty well from the sketch. Here are my thoughts: The squared bag shape would only retain that shape if the contents were solidified, as would happen with a soil/cement mix (which you specify); looser material would eventually force the bags into their more natural oval shape after the form were removed. But then, I wonder, why bother with using the bag material at all? What you describe is pretty classic rammed earth with lifted forms, and there would be better adhesion with rammed earth directly upon rammed earth rather than with the bag material intervening.

I might mention that rammed earth is often formed with slip forms done in lifts of maybe 2 feet. The proper soil mix is 15-30% clay and the rest sand. Sometime a small amount (maybe 5%) of Portland cement is added as a stabilizer, but not always. This is one area where earthbags have an advantage, because you can get away with a larger variety of soil mixes. Your suggested mix of 30% cement to 70% soil would be equivalent to a 3:7 mix of cement/sand concrete, which is very rich in cement! Standard soil cement mixes call for between 6 and 16% cement, depending on the specifics of the soil and the intended use.

If the purpose for forming the earthbags this way is mainly to reduce the work and material in plastering, I have to say that I don't find the standard approach objectional. All those crevises between the bags give the plaster much better "tooth" than a smooth wall would, so there is an advantage to leaving these voids. I should add, though, that the apparatus and concept is very clever, and shows great inventiveness; I suspect that it would actually function quite well as drawn.

C: This device was inspired by one I saw on a site featuring the Natural Building Colloquium in Texas 2007. I took the concept and redid it to my needs ended up with a new device. Here is a picture of it:

Q: I am planning on building a 30' diameter earthbag home within the next year. I am also thinking about using reject sand and adding papercrete, perhaps 50% as an additional binder to harden as a concrete wall plus added insulation. May I have your opinion?

A: I think that you might run into some significant problems with this scheme, primarily related to the addition of papercrete into the mix. It might work if the papercrete is allowed to cure (dry out) completely and then is kept dry for the rest of its life, but this may be hard to accomplish. If you are building vertical walls, then a roof with substantial eaves can protect the wall, but if you are building a dome with the bags, then it is very difficult indeed to assure that the papercrete is kept dry, and the consequences of damp papercrete can be unhealthy mold and inefficient insulation.

Q: I have the opportunity to build an earthbag dome at a friend's property. There is a large quantity of ash available from a boiler which burned wood and trash. Can I use the ash at 100% for the bags?

A: It is hard to say how well the ash would do in the bags, although I suspect that it would be fine. It may compact some, but if you tamp it well enough, that shouldn't be a problem. I would think that the ash is rather inert and would remain solid over time. Some experimentation would be in order.

Q: Is there an estimate of soil needed to fill each bag and the filled dimensions so I can calculate how many bags I will need and the amount of soil to fill the total area?

A: With 50# rice bags filled only full enough to be able to fold the top flap over to seal the bag when placed on the wall, the face of it will be about .7 sq. ft. and the bag will hold about  .8 cu. ft. of material.

Q: I wonder - after reading about your designs - how compactable the volcanic 'crush' filled earthbags are once installed. Do they 'set-up' like the ones Kaki Hunter and Doni Kifmeyer advocate?

A: The volcanic stone does compact some, but never "sets up" like Kaki and Doni advocate. I disagree with them about the need for this degree of solidification, and have proven this through the construction and durability of the house I built.

Q: Do you have any recommendations regarding using rice husks? We are a rice producing nation, and these husks are usually gathered up and burned--obviously both a waste and a contaminant to the environment.

A: I have not experimented with filling the bags with rice husks, so I can't speak from personal experience. They do seem to be an excellent choice from almost every standpoint. They are obviously going to compact more than most mineral materials would, so you need to take this into account (but then so do strawbales, and people do build load-bearing structures with them). Also, I would be especially careful to protect rice-filled bags from getting wet, as I am sure the husks are more prone to rot than mineral materials. The advantage is that they provide excellent insulation.

Q: I was wondering if you think sawdust in an earthbag as infill in a Larsen truss wall would work, and if so how well? We are building in Kansas.

A: A bit of research reveals that Larsen trusses are lightweight rigid frames that are installed outside existing load-bearing walls, as a method of creating a large cavity for super-insulating a house and providing structural support for the new sheathing on the wall. Sawdust has been traditionally used as insulation, often mixed with lime to discourage insects, in wall cavities in the old days. I see no reason why your idea wouldn't work, especially if all general precautions for safeguarding the wall from moisture are made. I am not sure what the R-value of sawdust is, but would expect it to be similar to cellulose insulation, and therefore pretty good.

Q: The northeastern Ohio (USA) area where I live has a considerable amount of clay in the soil. Digging down just a few feet often reveals one- to three-foot layers of it. I've seen both red clay and white. Would this be suitable for earthbag construction? If so, what sort of preparation would be required prior to loading it into tubes or bags?

A: Usually it is recommended that a mix of about one third clay with the rest sand is best for filling the bags, because the straight clay has a tendency to expand or shrink, depending on its moisture content and the sand tends to stabilize this.