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: What kind of fill material do you need (clay...)?

A: You can fill the bags with a variety of soils, including with some clay, but it is probably best to not use more than about 30% clay so the material doesn't shrink or expand with moisture.

Q: You used volcanic rock material to fill your 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: Under what conditions would you recommend stabilizing the soil mix with lime or Portland cement?

A: Soil stabilization is rarely needed in earthbag construction. Under some circumstances it might be advised in parts of lintels or arches to make them more rigid, or if the fill material is too loose, such as with very fine sand, that doesn't want to compact into a solid.

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: 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: 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: 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: 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 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 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: 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: 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: 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: 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: 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: 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: 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:   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: "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: 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.

Q: I'm preparing to build an emergency shelter using the CalEarth book and DVD and plan to use clay & sand mixture from my property. I understand the ratio is important so my question is: What is the correct ratio and where can I get a soil sample analyzed? The instructions mention keeping the soil moist when filling the bags, but not how moist. I'm puzzled. I'm 81 years old and am really enthused about this project.

A: With earthbags, the exact proportion of clay to sand is not nearly as important as it would be with adobe or rammed earth construction. Anywhere from 5 to 35% clay should work fine; ideal might be 15 to 25%. You can figure out the relative % of your natural soil by doing a jar test. Fill a clear glass jar about 1/3 full of the soil, then add water to nearly the top and shake the whole mixture vigorously. Then let it stand for a day to settle out. Eventually the solids will settle to the bottom and the water will be fairly clear on top, with perhaps any organic material floating on that. On the very bottom will be the heavier aggregate, then above that the courser sand and then finer sand, and finally on the very top will usually be a clearly marked line of clay. Then you can compare the amount of each layer to determine the composition of your soil. You want the soil just moist enough so that it will compact and stay in a ball if you squeeze some in your hand...you don't want gushy mud.

Q: When I did the jar test (5 times in different areas), I found that in all test I only had a 1/8 '' line of clay at the top which would equate to about 1%. So my next question is this: When I process my soil for filling the sandbags and mixing the cob, (I plan to pile up a big pile of sand and put into a small cement mixer about {10}  3# coffee cans full of sand) How much Portland cement or lime should I add to the mixture? And which is preferable cement or lime? 50 years in the aerospace industry, several phases of engineering and I feel so stupid.

A: The requirements for cob are much more stringent than for the earthbags. You really need the clay in there to bind it all together for cob. I suppose that you could add enough cement or lime to serve this purpose, but this would not be true cob; it would be more like a soil-cement mix. This is a dry pack (moist) earth/cement mixture which works especially well with rather sandy soil, but will also work with other soil types. The heavier soils with more clay content will probably require more portland cement. Soil cement has been used to form walls, make floors, pave roads, stabilize river banks, etc.

Here is some information about formulas for soil cement: Make it by mixing earth with Portland cement to the desired depth, add water and mix again. Tamp, and cover with plastic to let it cure properly. Use 6 to 16 percent cement by volume according to the density of the soil. The denser the soil (clay, for instance), the higher percentage of cement to use. Six percent translates to 1 part cement to 15 parts soil; 16 percent translates to 1 part cement to 6 parts soil. The cement could be replaced by hydrated lime, and this would be more environmentally benign since there is a net zero CO2 emission associated with it, but this will not be quite as hard and durable as cement. I would recommend doing some experiments before committing to this for a large project.

For filling the earthbags, you could also do this, but I question whether it is really worth all of the trouble. Nader Khalili only considered the bagging material as a temporary form for adobe (thus super adobe). He liked the idea that the bags could rot away and the building would still stand. But in order for this to be true, the bags need to be filled with a hardening material. A whole other approach is to fill your bags with your native soil (unaltered), allow the polypropylene (which is incredibly strong) to remain as a containing skin, and protect the bag material with a plaster (which you were probably going to do anyway). In order for this approach to be viable, you have to protect the bags from the UV in the sun as much as possible, so you would want to tarp them when you are not working on the wall. I built my whole house this way (filling the bags with crushed volcanic stone...which is better insulation than soil) and it is still standing after 10 years and will probably stand for at least another century I believe.

Q: Can you tell me how well (if at all) earthbag works with topsoil? Or does this have to be the clay/sand/gravel?

A: There are various opinions out there about appropriate fill material for earthbags; some feel that only a sand/clay combination is appropriate, because this will harden into a monolithic block when it dries. I am of the opinion that you can fill the bags with almost any kind of mineral material, whether it "sets up" or not. The key to this is making sure that the integrity of the bags is not compromised, either during construction or over the life of the building. This means that you need to be careful to keep the sunlight off the bags as much as possible during construction, and make sure that a good plaster is maintained over the bags. Another thing to be careful of is to make sure sharp rocks will not puncture or tear the bags...or that organic material will decompose in the bags. In some circumstances, pure sand is not advisable, since it can shape-shift and cause instability, especially in domed structures.

Q: I am with the faculty of fine arts, Alexandria University, Egypt. We need help with our earthbag building. We are having problems with the dome part. It is collapsing and we cannot keep this from happening. We have bags of cloth, with a diameter of 30 cm, and are using dry, pure, yellow sand. The students are so happy to build with the sandbags, me too...we need to continue.

A: I am so sorry to hear about your problems with building your earthbag dome. I suspect that your main problem is the sand you are using to fill the bags. I also had a major problem with the first earthbag dome that I tried to make; it also collapsed because I was filling the bags with pure dry sand. I suspect that some kinds of sand might work for this, but the sand that I used (and apparently you as well) is too "slippery" to stay in place, especially when the dome begins to incline more and the force of gravity pulls on the sand. With vertical walls, it would probably be fine, but not with inclined walls. What happens is that some kinds of sand do not pack firmly together, and instead will easily shift position within the bag. The solution would be to either find some other soil to fill the bags, or at least to add some clay (10-30%) to the sand that you have. Another solution would be to stabilize the sand with some Portland cement, or possibly some lime and dampen the mix before bagging it. I know that Nader Khalili at one time said that the bags could be filled with sand, but experience has shown that this doesn't always work. In fact, he eventually resorted to using a pure adobe soil for his "superadobe" sandbag works, and stopped relying on the bags to remain a structural part of the building.

Also, from the picture I can see that the bags you are using are fairly small in radius, which would give them more a tendency to roll off as you build, especially given that I see no barbed wire placed between the courses. It appears that the bags weren't tamped very much as they were put up. All of these factors might also have contributed to your collapses.

Q: The problem we face is that you have to separate the earth from the organic layer and then pass the earth through a mesh to obtain the smaller grains which separate from the rocky type mass. Lots of material seems to get wasted in such process and I have never-ending piles of earth lying on different locations around the hole and where we mesh the material. If you don't have a machine to do this job and only count with manpower (like in so many places where we want to encourage such constructions) this task is a rather long and a tiresome one.

A: All of that sifting and screening is not necessary in my opinion. Small stones in the mix will have no adverse effect. Even small roots will not really be a problem...just avoid large stones and most organic material.

Q: I live in HI and plan on building an earth bag wall for the perimeter fencing for our land. What's the correct mix of cement to cinder and do we mix the bag fill dry or wet?

A: If you add cement, you need to dampen the entire mix before putting it in the bags. You certainly need no more than 10% cement, but I question whether you need any...

Q: My wife and I finally managed to spend a bit of time on the land we bought in Georgia over the weekend, and we took some soil samples and did the settling test on them.  To me it looks as if I've got about even thirds sand, silt, and clay, but I wanted to bounce the pictures off of somebody with more experience.  The pictures are attached.  Does this seem like a reasonable soil mix for earthbag building?

A: I would expect this to be excellent soil for using in earthbags, or other earthen building projects, such adobe, cob or rammed earth. If you dampen the soil slightly before filling the bags and compact it well, the earthbags should become nearly rock hard and be quite durable. In this circumstance, the bag material becomes less important to keep the structure erect.

Q: I live in upper east TN...my soil is very dark rich loam...will this work in the sandbag?

A: Virtually any soil can be used in earthbags, but it is best to avoid heavy clay soils or fine, slippery sand. As long as you remove most of the larger rocks and organic debris, you should be fine.

Q: I am starting a music studio in my basement and thought of building the dividing walls out of sandbags. Do you have any experience and tips for me with regards to building sandbag walls (straight or slightly curved) up to a concrete ceiling?

A: Bags of sand are very HEAVY, so make sure that the floor can support them; a concrete floor in a basement is probably fine. Especially for a music studio it might be better to fill the bags with rice hulls, straw, or volcanic rock to better absorb the sound rather than bounce it. If you curve the wall a bit it will be more stable.

Q: I am building a garden wall in Ashland, OR.  I've put rubble in the trench and got two courses of bags with cinder stone done, and I'm wondering about the next step, which will occur when I start bagging the dirt that I've collected from the area I'm enclosing with the wall.  The dirt around here becomes rock-hard when dry, over the summer, but it's quite greasy and sticky when wet, as it is now during our Spring rains.  When it's this wet, it sticks hard to shovels and needs to be pried off regularly.  So I don't want the dirt to be too dry, or it won't form a hard block when it dries, but on the other hand I don't want it to be too wet, or it will be practically impossible to bag and will change its form as it dries in place on the wall which might create a shift.  (Although in the bags I've experimented with, it really doesn't seem to change its volume much at all.)

Possible plans :
1)  Wait for the right moment, when it's "just right", neither too wet nor too dry, i.e. dry enough to bag but not so dry that it won't cohere, and for that I just have to experiment. 
2)  Perhaps it's not necessary for the dirt to become a hard block. Before it dries too much, it becomes pebbly.  If it's almost dry but still pebbly, is that okay as long as it's packed firmly?  In that case, I imagine it would be sort of like the seashell stuff that I've seen on your website. 
3)  What about bagging it and laying it when it dries just enough to form a pebbly texture and then wetting it down with a hose when I have a course laid, then tamping it to help it form a firm block?

A: The soil that you describe obviously has quite a bit of clay in it. Clay is not the ideal soil for bagging, for the reasons that you give, and also some clays are very expansive when damp, which could affect the stability of your wall over time. Some clay is a good thing because it will bind the courser grains of soil together, but ideally there would be no more than about 30% clay, and the rest a sandier soil. For a garden wall it may not matter much if it expands or contracts a bit over time, in which case you can do your bagging whenever the soil is easiest to work. The main likely problem will be some cracking of the plaster you put over the earthbags to protect them. To avoid this possibility you would need to either mix some sand in with your clay (which is obviously a lot of work) or have some better soil trucked to your site.

Q: I am planning on building a sand bag house in the dome shape. Can you tell me is it necessary to use a small percentage of cement in the earth mix. My local soil has a great texture which allows it to be compacted quite hard. I plan to clad with chicken mesh and then plaster over.

A: There are differences of opinion about the need to stabilize soil before filling the bags, but in your situation I would say that to do so would be overkill. If your soil packs well and you plan to reinforce the plaster with chicken wire then you are certainly safe to proceed without cement.

Q: Won´t there be a problem if I place the heavy roof on the walls made with bags filled with balastre (the red volcanic rock)?  You know, because it´s fragile and it´s light.

A: I wouldn't worry about the "balastre" being able to hold up your roof. Once it is compacted a bit it is just a strong as solid adobe. If you want to be sure that it will be plenty solid, you might make a steel-reinforced concrete "bond beam" at the top that will help distribute the weight of your roof structure.

Q: We have a small winter home in Baja Mexico and want to construct a workshop/generator room using sand filled bags. I would appreciate any advice as to whether adding cement to the bags would be of value and if so what ratio sand/cement.

A: Adding cement to the soil you put in the bags will definitely make it more solid, but may not be necessary. If the your local soil packs into a fairly solid mass when tamped, then it is likely OK to use as is, especially if you protect the bags with a good plaster.

I guess I should have written that I will be working with straight sand with absolutely no soils of any sort.

Some sand will pack pretty nicely, but other sand will not, especially the very fine, spherical sand that is a shape-shifter. If your walls are vertical, then even this can be used without cement, but for domes I would suggest stabilizing with cement, or added clay.

Q: My friend used 10% cement in the mix for his earthbag dome. I am not thrilled about using cement myself. But the east side of the Big Island is way way humid, rains every month. My land is like 25 miles from his and it is slightly less humid. I'm thinking about 5% cement in the mix for my project. There are several people on the Internet that claim that you don't need cement at all. I could see that kind of reasoning on cost factors, cement is not free at all. But I also think that by skipping cement the earthbag building becomes temporary. If my earthbag building is going to start to crumble in 20 years because the humidity is taking a toll, I cannot claim superiority over wooden structures, which begin to rot if not properly treated against termites.