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Q: I would like to use existing site material, a heavy clay, without amendment. Is this feasible? 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. 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?
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. 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...
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.) 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. 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. My property is really close to the lava flow, and lava rock is everywhere. My friend wants me to use his silt/cement mix, which means buying the silt and having to unload it by truck. I'm thinking on somehow using that lava rock in the mix, but it might take too much physical energy to crush that lava with simple tools. And I'm not sure on how good the lava powder is against humidity.
I'm not sure we are talking about the same thing. You mentioned that you used crushed volcanic rock in your Colorado site. I am talking about lava rocks abundant in my property. Can I crush my lava rocks with hand tools, or maybe a bulldozer to get some fine powder for the mix? Would the resultant powder be of any quality for the earthbags? From what I can see in the pictures the lava rock you have there is similar to what I used. The main useful quality about what I used (which was red) is that it is very lightweight, full of air pockets, so that it acts as a natural insulating material. If it is crushed to a powder, then this quality is diminished considerably, so I made sure that I eliminated as much powder as I could before using it. I used a pre-crushed gravel that averaged about 3/4 inch, but somewhat larger or smaller is also possible. If you were able to use this, then you wouldn't necessarily need to use any cement at all...I didn't. Q: My wife and myself are considering building a small house in a desert Oasis, in Egypt. As you may know, the main material available over there, besides Palm trees and salt blocks, is ...sand, sand, and sand! I do not know what are the limitations, drawbacks or advantages of using sand instead of another non-available material. Do you think the result (stability, thermal isolation, humidity, long lasting, etc..) could be positive ? A: I have had some experience building an earthbag structure with sand. My first experimental building was done this way, and unfortunately it didn't turn out too well. The problem was that the sand where I was building (near the Great Sand Dunes National Park in Colorado, USA) was a very fine, rather spherical sand that didn't want to pack into a solid form in the bags. You might say that it was a "shape shifter," so that when I was up to about two meters high with this little dome, the wall simply collapsed. I rebuilt the dome using some local crushed volcanic stone. This doesn't mean that you can't use the sand that is available to you; it just means that you need to be careful about using it. Some sorts of sand, like a sharper river sand, does pack well. Even if your sand is more like what I tried to use, you can stabilize it in various ways, through either adding some cement and wetting it before you fill the bags, or possibly adding some clay to the mix. Lime is another possible stabilizer. In any case, I suggest that you do some experiments to see what works best, before committing to a large project like a house. The real drawback we find with sandbags is the necessity of having at least 3, 4 or 5 persons around working on the project. Regardless of budget (and bearing in mind that red bricks are quite cheap in Egypt), one positive point about using bricks (clay, mix, cob etc..) is that one can still work alone, or two people can work on different parts/areas. Q: I'm trying to find urbanite, but so far all I've been able to find is broken up asphalt from a parking lot. Is this an ok substitute for cement? Will it off-gas? It would be used in a stem wall for a straw bale building on top of a rubble trench. Both sides would be coated in a lime/perlite stucco for better insulation. A: I would not use asphalt chunks, not only because they might off-gas, but because they are not really all that solid over time and can easily "melt" and therefore settle. You are much better off using concrete chunks or gravel. Q: I've found a statement that "you would only want about 30% clay to 70% sandier soil" to avoid the dangers of shrink-swell that many clays exhibit. I've also run across the comment that "soil stabilization is rarely needed in earthbag construction". It seems to me, however, that the troubles of expansive clays could be eliminated by completely stabilizing the clay with hydrated lime. My site is rich nearly pure red and gray clay that is known to be "severely expansive", predominantly montmorillonite. It has no sand to speak of. Having done my own experiments, I found I can eliminate the clay's shrink-swell property with hydrated lime (8% w/w dry); with some water it turns it into a highly workable moist dirt that, when dry, shows more than 100 psi unconstrained compressive strength. I would like to know if anyone has used only clay, completely stabilized with lime, as a fill material. If so, where might I find guidance beyond my own experiments? If not, does my description of the properties make this clay seem viable as a sole-ingredient for use in earthbag construction? Would I be recommended, nevertheless, to include sand in the fill material and, if so, how much and why? A: I have not heard of people stabilizing pure clay with lime, although from your experiments this sounds like a promising approach. If doing this eliminates that expansion/contraction cycle of clay, then this material should make an excellent fill material for earthbag construction. I suggest that you do some further experimentation with a small project and see how it fares. In my experience pure lime plaster also will shrink quite a bit when it dries, which is one reason that it also needs some sand added to keep this from happening. It is a mystery to me how both clay and lime mixed together will not shrink! C: Isn't lime a wonderful substance? The chemistry of its many uses seem straightforward, but it is chemistry. Actually, the pozzolanic reactions of hydraulic cements are more complex. Q: I do like the scoria approach, but I don't think we have much in the way of volcanic rock in my neck of the woods. I'm going to check into perlite to see if that's available hereabouts and if so, if it would be an affordable alternative. But if that doesn't work, I'll probably have to scrap the bagging idea and go with some other approach. A: (Owen) Perlite, scoria, vermiculite and rice hulls are all good options. Rice hulls are still experimental and it would be helpful to get more info on how they've worked for others. Although rice hulls are resistant to decay, they will rot if they get wet, so I would use them only in dry areas with a good roof (no domes). Price each one and see what's the most affordable. For scoria, check with landscape suppliers. You can get perlite and vermiculite from gardening supply outlets. Try to buy things direct by the truck load. Q: What is the best bag filling to deal with high moisture content and heavy rains? A: The most secure fill material for earthbag buildings would be Portland cement stabilized soil, as this could actually survive some immersion in water for a period and still retain its shape. Q: I recently acquired a .50 acre parcel of land in southwest Florida. I've been wanting to build an earthbag home for the longest time. Iis half an acre enough to build a 3 br/1.5 bath earthbag home, taking bag fill from the actual land? A: The best fill material for earthbags in Florida would be some that is a combination of both clay and sand, in a ratio of about 1 to 2. If your property has these ingredients, I'm sure that your half-acre would suffice; it doesn't take much land area, especially if you can dig down vertically to access it. A: (Owen) It shouldn't take many truckloads of clay to give you the necessary proportions. I would experiment to find a stable mix by adding increasing amounts of clay. Keep track of the percentage of clay in each sample. Once you get a stable sample, calculate the approximate volume of clay you will need. On a small house, I'm guessing two truckloads may be enough. This is just a guess, so do the math and calculate how much it will cost. Q: I'm testing bags for my construction and my soil is nearly 100% clay. I trucked in some sand and mixed an experimental bag with 1/3 clay soil and 2/3 sand. I mixed it dry in a wheelbarrow and broke down the clay as small as I could but most of it still stayed in small clumps. I mixed with water and filled a test bag, tamped it down very well, and it's been sitting there for 3 days. The bag weeped some water but not very much. When I press on it, it still feels more like sand than adobe. Should I mix a different ratio of sand to clay, pulverize my clay into finer dust, or just keep waiting and hope this bag eventually sets up correctly? A: I suspect that your test bag will eventually harden up just fine, but it might take awhile. If water was weeping out of your mix, it may have been too wet in the first place. A: (Quentin Wilson) Just use the soil you have. The problem with too much clay is that sun cured adobes crack. Since you have the soil in bags, cracking is not a problem so you don't need to make the job any harder than it is. Any clay that oozes through the mesh will just help stick the bags together. Assuming that you are using the dratted woven polyolefin or polysomethingelse bags, they have such a low coefficient of friction that keeping them aligned as wall go up is troublesome. The oozing clay goop will help. Being old fashioned, I prefer hemp, jute or cotton bags. Don't worry about clumps. Moisture will suffuse throughout the material over several hours or days as it slowly dries. If that seems sleazy, let the soil sit in a pile for a week or two that you keep damp. Nature will do the work for you. If you come back in 10 years and for some reason (such as solar degradation when plaster is gone) you will find that the bag contents will hold up on their own even if it does not seem to be a perfect blend in the beginning. A: (Michael G. Smith) Sounds to me like you are either using too much water or not tamping hard enough. No matter what's in the bag, it should feel very solid once it's been compacted. Q: What parameters make for good earthbag fill? Here at the office we often talk about, ‘select fill' and ‘general fill'. I wonder if either would be suitable bag fill material. Are there any specific recommendations for good fill? A: The best fill for earthbags is similar to soil that can be used for making adobe blocks, cob, or rammed earth walls, although for earthbag construction there is more leeway for the ratio since the bag will help consolidate the material. In general soil that is between about 10% to 35% clay, with the remainder primarily sandy aggregate works well. When filling the bags you want to moisten the soil just enough that it will form a solid block after being compacted, but not so much that it will weep water. Once the compacted soil dries it will be quite hard and brittle. Q: My husband and I have just purchased land in the hills of Montana and will start a test dome shortly in preparation for building a home next year. I have been searching locally for scoria for the bag filling. All I can find is 3/8" or 1.5". I'm a bit worried by that - the 3/8" may be on the small side and so may not have adequate insulating properties, but the 1.5" may be too bulky and untampable (if that's a word!). Perhaps we could mix them. A: I think that your suggestion to mix the two sizes would be the best, but try to order the stone with as little fines as possible (or even screen it out yourself) since the fines will also lessen the insulative value. Q: My concern with road base is based on what I hear about some having clay and other types of road base not having clay. The people at the recycle yard could not really tell me much about the contents. I have been adding clay to the recycled fines and that works well, but the nail split the sample in a few pieces. A: Driving a nail into most earthen blocks will crack them. I think the deck screw idea tends work better (at least according to our adobe expert). "Road base" is a generic term that applies to a large range of specific soil compositions, depending on the locality, so your addition of clay may make the difference with how well your particular material consolidates into a solid block. The thing about earthbags is that the fill material doesn't necessarily need to form a solid block, since the bag material itself will hold it all together. Q: I am going to build an addition to my main home. I am using earthbags to build the walls. I am going to build a rubble trench. I am going to fill the bags with crusher fines from a local rock quarry. I guess the fines are a bit larger than ag-lime. Would ag-lime work as filler or should I stick with the fines? Should I mix some sand in with the fines or can I use straight fines or straight ag-lime? The walls will be load bearing. The addition will be round with a masonry stove in the center that will be load bearing as well with timbers running off masonry stove to the earthbag wall. A: As for fill material, the ideal is something that will solidify after compaction, like a moistened adobe soil would. Adobe has a combination of about 1 part clay to two parts sand. Your crusher fines might do this just fine, or possibly also the ag-lime, or even a combination of the two. I suggest that you run some tests to see what works best. Make several mixes, moisten them slightly, place them in small bags, tamp them well, and wait for a week or two and see which ones remain solid when dropped or handled. I doubt that you would need to add sand to the fines, but they may need some added clay to bind them better. Q: I am not quite sure that the numbers for hydrated lime add up as Kaki suggested. I was close to buying a couple of hydrated lime bags to do some testing and pay for some PSI certification from a local lab. But on a cost basis, I don't see how hydrated lime is going to be cheaper than cement. On the Big Island, a 94 pound bag of cement costs close to $15. On the other hand, a 35 pound bag of hydrated lime costs close to $12 In the cindercrete mix we use around 8 parts of cinder, 1 part of blue rock, 1 part cement and 1 part water. If we are going to use 1 solid part of hydrated lime, it is just too expensive. Unless Kaki was talking about 1 part of very liquid hydrated lime paste. A: I doubt that Kaki was suggesting that you use the lime only. From my experience, pure lime will shrink a great deal as it cures (and it takes a very long time to cure). You need to add sand to the lime to make it stronger and keep it from shrinking too much...sort of like adding sand to clay to make adobe. I suggest that you try replacing the cement in your formula with the lime and see how well this performs. It doesn't need to set up to the specs of concrete, only become firm enough that it will stay in place without shifting over time. Then if you leave the bag material on before plastering, your wall will be extremely durable. Lime is considerably lighter than cement per volume, so that 35 pound bag will go almost as far as the 94 pound bag of cement. Q: We have land with at least 169 different soil types. But the area for building is a heavy mix of sand, with a small amount of clay. We planned on using some portland cement mixed in with our soil. So if we cover them with a tarp for a week or so after installing them that would give us a sufficient cure time? A: I suggest that you keep one test bag separate from your wall and use it a guide for how long it may need to be cured; there are so many variables in all this that it is hard to say in advance.
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Are scoria and/or perlite filled earthbags as sturdy and even bullet proof as are those filled with sand or dirt? Q: I went to the Lava Rock facility to get a price list and to see the scoria. Their 2009 price list showed one ton of the 3/8 inch or less material for $16 a ton. I have a feeling you used something larger than that. Am I correct? Q: The building people are concerned with what the material is made of. Since I have the same type of climate that you do in CO I want to go with the lava rock. A: While lava rock worked well for me, since it provided excellent insulation, I suspect that the building officials will recommend the adobe-like soil. Q: I know a missionary in Niger that is interest in earthbag building, but he is concerned that the local sand is too fine, thin, and dry for that system. A: It might be that the local sand does not pack well enough into a firm block to be good fill material, but this can be amended with some clay or even cement or lime and dampened to help it solidify some. Q:
I thought the mixture was 10% concrete / 90% sand, (more or less and I know this is varied depending on location) moist but not dripping. If you use a machine to fill the bags you'll have lots of dry bags to stack. Does that make the finished structure weaker? |
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Kelly Hart is your host at greenhomebuilding.com, and has built his own home using the earthbag technique, which can be seen on 
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? 
Q: I am having a bit of trouble discerning the clay to sand proportion of my soil and have attached a photo in the hopes you can give me your opinion. Do you think it is possible to use this soil for earthbag building without mixing any other soil or sand with it? How about for Adobe or cob? I realize it is difficult to tell by looking at photos but perhaps you can give a hint before I begin experimenting. I am really hoping I will not need to truck in other material.
