Earthbag Building: Filling and Laying Earthbags

Q: I am considering building a small earthbag dome with tubular bags. The fact is that here in Italy, the only tubular material I can find is polyethylene, not polypropylene. Have you any experience with polyethylene? What could the difference be?

A: I have no experience using polyethylene bag material; I have only used polypropylene. I know that polyethylene is the most common type of plastic in use today, and that it comes in many different formulations, each with different characteristics. For earthbag work you want these qualities:
Strength--can withstand considerable pressure without stretching or breaking.
Durability--will last for hopefully centuries without degradation, especially when protected by a covering of plaster, and is not adversely affected by moisture or normal temperatures.
Low cost--not too expensive for common use.
Availability--readily available in a form that can be used. I suggest that you check with the manufacturer of the material in question and see how it compares to polypropylene, which rates very high in each of the categories.

Q: Looking at bags, I see gusseted and non-gusseted available. I'm assuming the standard for construction with earth bags is the non-gusseted. Is this correct?

A: I've used both the gusseted and the non-gusseted bags, and actually prefer the gusseted ones because the base of the bag doesn't produce pointed protrusions that need to be hammered back into the wall to make it smoother before applying a plaster.

Q: I would imagine that using Polypropylene would not be very 'green' because it is a 'plastic'; how can your building be properly 'breathable'?

A: The poly bags are certainly a plastic, so in that regard they are not very "natural". Burlap bags are more natural. However, I feel that their use is justified by their superior strength and rot-resistance over time. They actually do breathe quite well because the material is woven from strands of fiber that allow air flow.

Q: I would like to build a home with stabilized earthbags and was wondering if you had any experience using natural materials such as burlap or jute instead of polypropylene bags/tubes.

A: I don't have any personal experience using bags other than polypropylene, but I know of others who have used jute or burlap bags. These bags are actually more resistant to UV deterioration but less so to moisture than the poly bags. This shouldn't matter, however, if you are planning to stabilize the fill material. The natural bags can be more expensive as well.

Q: What is the ideal width of an earthbag wall or the recommended dimensions of the bags for this application?

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: 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: I live in Arizona; where is a good place to purchase polypropylene earthbags for building?

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 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: 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 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. The use of small bags that form 12" walls are really too small for most projects other than low garden walls and such. Nearly all of the significant earthbag projects that I am aware of use larger 50-100 lb. bags that measure closer to 15" X 24" X 5" when compacted. 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 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.

C: We used polypropylene sandbags when I was in the Army. My experience from those days was that the poly bags installed in a wall and then bermed with earth (so that there was no UV exposure) would deteriorate fairly quickly if the soil in contact with them was consistently damp.

A: When I removed some of the earthbags that I had used to make a dam some 6 years prior I found the polypropylene material to be as strong and pliable as the day I put it in the ground. Roots from the nearby tree had found their way into the bag, which was partially covered by a sheet of plastic, so any moisture that got in there did not easily evaporate. Of course this is a short time for such a test, but none-the-less you would expect some degree of deterioration from the moisture contact over that many years if it were to occur. I did a bit of internet research, and came up with the following quotes:

"The main concern for PP geotextiles is to prevent thermo- and photo-degradation by using proper stabilizers."

"Polymer degradation can also result from mechanodegradation, which is caused by the application of stress such as high shear deformation. The stress-induced degradation may result from comminution (grinding, milling, or crushing), stretching, fatigue, tear abrasion, or wear. Nonetheless polypropylene has good chemical and hydrolytic resistance."

I think it is quite likely that the bags you remember were already compromised by UV exposure, as it really only takes a few weeks of being in the sun for this to occur. PP earthbags are currently being used as foundations for strawbale and other types of alternative structures, and often they are filled with gravel to avoid wicking action upward, so the fill is not consolidated into a firm material, like rammed earth and the integrity of the bag is crucial to the longevity of the building, as it is with my earthbag house, since the bags are filled with crushed scoria.

Just a few days ago I checked the exposed poly bags in our old pantry in Colorado, which are not exposed to sunlight, but are out in the interior air and occasional light. I gave one of the bags a good poke with my finger and it felt as strong and supple as the day I stacked in on the wall, which was over a decade ago.

Q: Mark is also a distributor of Cal-Earth bags, which I believe have some kind of patent. I am tempted to trust him that they are superior to regular bags, and without knowing exactly why, I will most likely use them in my earth dome building in Hawaii. But I'm not quite sure, I will use them in El Salvador for my sister's project. It might be too expensive to ship the rolls in a container.

A: I actually don't think the Cal-Earth bags are any different than other bag material...they have just been printed with the Cal-Earth words. Polypropylene is polypropylene, even if some of it has been coated with UV retardant. Nader did not patent this...he just realized that you could use the long tubing material for building instead of individual bags, which are also made from the long tubing. You can buy these rolls from the manufacturer for less than you can from Cal-Earth. I prefer to use the misprinted individual bags, which are cheaper yet.

C: After watching your DVD, this is my own conclusion of why Cal Earth bags are superior. It's not that Cal Earth bags have a superior manufacturing process than everyone else. It's just that Cal Earth is not really selling bags, they are instead selling you the rolls from which you make your own bags.

I could see myself trying to hold together hundreds of small bags. It would not be easy, and if I am not that careful, I would have several bags sliding over on a daily basis. At Mark's earthbag dome in the Big Island, we had close to zero bags sliding over. Most of the time we were filling out long tubes, which is another name for a custom size big bag. Sometimes the whole row was one big tube, and as we went up the tubes got smaller.

Part of my job was to use scissors to cut from the roll, and then using a needle and wire I closed one end of the bag, and then I was ready to start filling it with earth. And the big help in making sure the tubes did not slide over was use of barbed wire. When the tubes are still wet, it is guaranteed that they are going to slide inwards if you don't use barbed wire. We found that out because of drying times which took close to a day, we could not do more than 4 rows per day.

We used small custom made bags on very few occasions, as fillers in difficult angles, and of course at the very top of the dome. So, I think that anyone else can get the same results if they buy rolls of material to make the bags yourself, instead of buying hundreds of small bags all the same size at pennies each. Yeah, I don't see why anyone else besides Cal Earth cannot sell rolls of bag material.

R: From my experience, I would say that with individual bags or long tubes, one is not superior to the other...they are just different and have different attributes. I used the small bags, partly because I worked mostly alone and it was way easier to do this with the smaller bags. I think you need more of a team (at least 2 people) to effectively use the tubing. I could fill the small bags with the light-weight volcanic rock that I used to fill them, carry these to wherever I was working and place them easily. I never had any problems with bags slipping off. I kept them laid horizontal and used the barbed wire, so they didn't really want to slide. I did have a problem with the tubing when I tried to use it once, because the loose material I used as fill did allow the whole tube to actually roll off the wall. Without the sewn hem at the bottom of each bag, there was a tendency for the tube to roll. But then for what you and Mark were doing, I can see how the long tubes were better...so it all depends.

Q: The sandbags I am using are empty polypropylene sandbags ( 14x26"), 1600 uv treated. They have been exposed to the sun from 6am to noon from 2 to 17 days. They are covered for the rest of the day. Today the tarp blew off and they were exposed to the hot desert sun. My question is how much exposure will they tolerate before being damaged beyond repair?

A: I used standard, untreated poly bags, and noticed that a detectable deterioration happened after maybe a month of full exposure to the sun. I don't know what the rating is for the treated products. My rule of thumb was to only leave those bags exposed that needed to be for the construction process, and then covered them up immediately. I also started a first coat of plaster over some of the finished portions as I progressed with the construction, but then I was working on a rather large project.

A: Usually what I have seen people using is about 18-20" wide, when flat, and would be about 15" wide when filled.

A: They both work just fine. Tubes might be slightly more stable or integrated, but with barbed wire the individual bags work well.

Q: Is it possible to find the continuous superadobe fabric tubing or is it better to use individual sandbags?

A: Both the tubes and the individual bags work fine, although there are some differences: tubes take more people to fill and lay them and often cost a bit more; bags are easier to find, fill, and may cost less. There are sources list for both here.

Q: The Hunter/Kiffmeyer book suggests a 17x30 bag as standard, that anything smaller will not do. But that's for a team (or at least two people) to fill in place; I, on the other hand, will be working alone, so I can't really be throwing coffee cans of dirt to myself. I assume I'll be filling bags ahead of time, like the pictures of the Sun House on your website. Unfortunately H&K's book says the 17x30 bags tamp out at 90-100 pounds, which would be a little heavy for me to lift into place after filling, so I've been leaning more toward the standard sandbag size of 14x26. What do you think, is that really too small? Maybe I could do two courses for a thicker wall?

A: (Owen Geiger) I agree with Doni and Kaki. At least 17"x30" bags are needed for wall stability. 14" wide bags would be about 12" wide once filled and tamped, and very prone to tipping over. You could do a double wall, but that's not very practical. You're talking about a huge amount of extra work. So keep looking until you get the right sized bags. Also, I suggest getting a helper, even a high school kid or someone who wants to make a few extra bucks. Earthbag building is very labor intensive, and certain steps like building upper walls almost requires another worker. Or you could fill the bags with scoria (lava rock). Anyone could handle bags of scoria by themselves. I'm pushing hard for scoria-filled earthbag construction.

A: (Owen) Try hard to locate new but used bags. Surely you must have pig farmers, chicken farms, etc. somewhere within driving distance. These places go through huge quantities of poly bags and should be eager to make at least something by reselling them. What do they do with their used bags? Someone is probably buying them up and reselling them -- maybe feed stores.

Q: I am carefully reading the instructions and wondering if earthbags are as sturdy as plastic tubing when it comes to the roof for a dome? Is there any difference?

A: Well the earthbags have worked well for me. When they get tamped together with the barbed wire they become a rather solid block anyway. The long tubes might be slightly more stable, but I am not sure of this. They are also more cumbersome to fill.

Q: If a house is built of sand filled plastic bags, will the moisture trapped in the bags cause mold?

A: Actually, the polypropylene bags are a woven fabric that breaths to some extent, so the contents can eventually dry out. Mold usually requires some organic material to subsist, so purely mineral earth doesn't necessarily provide that.

Q: An ad on Craigslist we have posted looking for donated bags has gained us in upwards of 2000 or more bags ready for pick up over the next week. Should these work?

A: (Owen) Check the bags carefully. They may be fine, but you need to check for good quality, strength, uniform size, etc. Maybe tamp a few trial bags using bags from each source and see how they withstand the tamping process. And be sure to store them out of sunlight.

Q: We'd be using old poly bags, or maybe the long tube-bags from CalEarth -- the CalEarth bags are what I've worked with before, but jeez they're pricey! We're in an agricultural community, so old feed bags are abundant.

A: If you can access used bags in reasonable condition, I would say go ahead and use them. I actually find it easier to work with individual bags...and it is certainly cheaper.

A: A typical earthbag wall is about 15 inches thick, although this varies with the size of the bag and the thickness of the plaster. Inner walls can be made in a variety of ways, with wood framing, etc., so this varies also.

Q: I have a question about diddling bags. Do you think it is absolutely necessary? I have found a gusseted polypropylene bag 15x5x31 that seems to work just fine. The bags are a bit more expensive but it may be worth the time savings from diddling.

A: I like gusseted bags, as they do keep the bottom end from pointing out. But even with the ordinary bags, the requirement to "diddle" the bags is much overstated and too time consuming I think. I simply took a hammer to the pointy corners and knocked them back into the bag before plastering, and that worked fine.

Q: I notice on the cal-earth website they use continuous woven bag tubing which can be cut into any length of bag required, as well as listing this 'tubing' as available in various diameters It seems a good idea, but does it have any real advantages over using ordinary same-size bags for everything?

A: Both the long tubular bags and individual bags work well for most earthbag construction, especially if the barbed wire is used between courses. There might be some slight mechanical or aesthetic advantage to the tubing, but this might be offset by the need to have a crew available to handle the need for continuous feeding and placing of the fill material; one person alone can build with individual bags. Also, the tubing seems to be more expensive, especially if you are able to source used or misprinted bags. The tubes do eliminate any problems occurring with bag bottom corners poking out and needing to be punched back in.

Q: The use of a bag full of whatever to start off a home makes no sense at all; the bag will disintegrate.

A: The polypropylene bags are actually quite stable if kept out of the sun...and in many cases they only serve as an initial form to contain earthen material that then "sets up" sufficiently that the bag is no longer necessary.

Q: How long will earthbags hold up in sunlight?

A: (Owen Geiger) It's difficult to know for sure how long earthbags will hold up in sunlight. Some brands fall apart pretty fast, as soon as a few weeks. Equatorial and high elevation areas may experience slightly more rapid deterioration due to increased UV levels. From what I have heard and read most bags hold up okay for about 2-3 months. The safest way is to buy tarps or black poly and keep them covered as much as possible.

However, tarps are prone to blowing around in the wind and can be a bit of a nuisance. If you're doing a large job, then you can either buy UV resistant bags, which cost more, or in the case of vertical walls do one wall section at a time (including adjacent corners) and apply at least one coat of plaster as soon as possible.

(Kelly): One good indicator of how long the polypropylene material will last if exposed to the sun are the tarps themselves, which are often the same material. My experience is that they just get progressively weaker as time goes by, and may show signs of exteriorization after about two months' exposure and usually by about 8 to 10 months it is pretty easy to punch holes in them with a finger. And these tarps are often supposedly UV resistant. Obviously the best thing is to not take chances and keep the bags covered at all times, except when working on them.

Q: Do plastic earthbag bags off-gas fumes like VOCs, etc.?

A: (Owen) I don't really know. There's no discernible smell, and I've never read or heard anyone warn of this. A quick search on Google didn't turn up anything. It's best to avoid all synthetic materials as much as possible, although in this case most people seem to agree the benefits of earthbags far outweigh any negatives. And keep in mind, the bags make up just a tiny percentage of the over all structure. And even then, they're buried behind thick plaster.

C: Superadobe bags, like most sandbags (earthbags), are made of Polypropylene. If you google for Polypropylene MSDS (material safety data sheet) you'll see that the only concerns for safety come from burning polypropylene in unventilated spaces (and coming in contact with hot, melted , burning plastic). It is a very safe material; its used for everything from water bottles, pill bottles, candy containers, yogurt containers, plates/forks/spoons, blankets, shirts …
thermal underwear. 100% Polypropylene is not recommended for clothing/bedding if there realistic risk of explosions (refineries, war-zones).

Ok, back to http://en.wikipedia.org/wiki/Polypropylene#Degradation Polypropylene, when exposed to UV breaks down into http://en.wikipedia.org/wiki/Aldehydes http://en.wikipedia.org/wiki/Carboxylic_acids So if you were to build your earthbag house in a hermetically sealed sun room (airtight), and if you were to leave your polypropylene walls exposed to sunlight to the point that they fall apart (say 1-3months for non-UV-resistant polypropylene). And all the polypropylene has all dissolved, and then you walked in there and tried to breathe in all the vapors, there is no chance it would do you any permanent harm. Ok, you might be disturbed by the smell and fall and hit your head, or you might get an asthma attack, but if you leave the door open for 5 minutes you'll be fine. In conclusion, practically everything will outgas, but you're safe if you open door/window daily (like when leaving/entering). Polypropylene is very safe.

We often get questions from people wondering how many bags they need to have on hand for some particular project. Is there a formula to figure this out?

First you need to calculate the total square footage (or square meters) of the wall you intend to build. This can be done by simply multiplying the length times the height, and then to be precise, you can deduct the size of the windows and doors from this…but I usually don't do this because it is better to over-estimate how many bags you might need, and also, you always need some partial bags to keep the brick pattern going.

If your wall is curved you'll need to figure out the running length of the wall by either making a scale drawing and measuring the length that way, or in the case of a circle you can use the formula Length = 3.14 X the diameter for this.

Figuring out the surface area of a dome is obviously more complicated, partly because there are many shapes for domes. If the dome is close to hemispherical (not recommended for structural reasons) the formula would be 3.14 X the diameter squared. If the dome more closely resembles a cone, then the formula would be 3.14 X the radius X the radius plus the length from circle at the base to the top of the cone. Either of these formulas could be used to estimate approximately what the area of your dome might be, especially, if that total is then padded by not deducting openings, or simply rounding upward.

As far as bag coverage goes, it depends on the size of the bag how much square footage it will cover. I used what were labeled 50 lb. rice bags to build my house. These measured roughly 5? X 20? when laid in a wall and compacted. That is approximately .7 of a sq. ft. A nominal 100 lb. bag might actually be considerably larger than what I used, so you'll need to run some tests to determine what kind of coverage to expect. The 50 lb. bags I used measured about 18? X 30? when laid flat.

Once you have figured out what the area of one bag might be after it is filled and tamped, then you can divide that figure into your total wall space to get the total number of bags needed. For instance, with the 50 lb. bags that I used, you would divide the area by .7 to get the total number of bags needed. In this case, for example, a 100 square foot wall would require roughly 143 bags.

Q: How big will 1000 bags do?

A: I used the 50 lb. rice bags, and each one will cover about two thirds of a square foot of wall area, so you might expect to be able to create roughly 700 square feet of wall area.

Q: Just wondering about an estimation of how many sand bags there would be needed to construct a 3m x 6m cabin with a height of 3m?

A: You can expect to cover about 0.075 sm/bag, so 54 sm would take 720 bags. You often need partial bags, and sometimes they get tamped thinner, so you might figure on more like 800 for the job.

Q: Do you have, or know of, a formula for calculating the yardage/tonnage requirements for earthbags? For example, if we were going to use 4000 14 x 26 bags (mostly folded over, only stapled at the doorway, like you do) of scoria, how would we calculate how much scoria to order? We have to allow for tamping, too.

A: The only way I know to calculate volume of fill material for earthbag structures is to actually figure it out mathematically, by multiplying surface area by the depth of the wall. There is a formula for the surface of a cone that you can use for you tipi shape.

I figured a 20% compaction for the scoria from tamping and therefore added 25% to my calculations. Is that a good figure to use?

You will get a little compaction with scoria, but I doubt if you'll get 20%...I would guess maybe half that; on the other hand it is better to error on the too much side rather than on the not enough...

Q: How do you ever figure out how many bags you need for a structure? I'd like to build a 14' cylindrical tower 18' high, with two upper floors, top one as a balcony.

A: I used the 50 lb. rice bags, and each one will cover about two thirds of a square foot of wall area. Your cylinder tower will have about 800 sq. ft. of surface area, so you would need around 1200 bags.

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?

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: 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:

A: There only a few circumstances where it may be necessary to do this, but actually puncturing the bag with rebar does not substantially weaken it, and the fill material rarely leaks out.

Q: I've been primarily interested in earthbagging for the low cost, but in my case any savings would be negated by the need to hire additional help. 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.

Q: You used poly 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: 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: 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: 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.

C: The thought of rust attacking barbed wire (in those paces where humidity is often between 90 and 100%) kept me from looking into earthbag construction at first. But when I realized that the barbed wire is most needed to hold bags in place until the earth has cured and dried, the lights went on. It seems irresponsible in very damp climates to rely for strength on a material that may eventually rust. But once the walls are cured, the longevity of the barbed wire is not as critical. I think of the bags and wire as a sort of formwork. The earth itself is strong enough once it has cured.

R: (Owen Geiger) As far as the barbed wire, it's embedded inside a dry earth wall and is coated with zinc. Old adobe buildings of 100+ years still have their nails intact, probably because the earth wicks moisture away. I think the barbed wire would still be there in 100 years.

R: (Kelly) I agree about the barbed wire; it will last a very long time, and even it doesn't most buildings would do fine without. I think there are some earthbag domes that rely on the wire to hold their shape under tension.

Q: Is it a must to use the barbed wire as binder? Since the cost of steel wire is very much on the higher side, and since I am going to build a small house, 10 feet high, can I leave the barbed wire? I intend to build a mud brick dome over the walls.

A: It is not absolutely essential to use barbed wire between the earthbag courses, especially if you are erecting vertical walls. The wire adds to earthquake resistance. You might use wire in the top few courses to help stabilize this area.

Q: With a double earthbag wall (two columns adjacent to each other), how can you connect the two columns?

A: Short chunks of barbed wire put in occasionally at right angles to the straight wire will work. I basically did this on the double stem wall of my Carriage House, and extended the short pieces out far enough to then use them to attach the stucco mesh later.

Q: I may build a simple, small home out of earthbags. One thing I'm wondering about is if I use 2 point barbed wire, am I jeopardizing the strength of the structure? I have an unlimited free supply of 2 point barbed wire. I was wondering if I use 4 or more strands between each row if that would be comparable to using 2 strands of 4 point barbed wire.

A: Four-point barbed wire is recommended because it tends to grab the bag material better than two-point wire, so that the bags don't slide relative to each other. In terms of providing tensile strength to keep the building from expanding from any outward pressure (especially with domes) two-point barbed wire would work just as well. I suggest that you go ahead and use the two-point wire just as you would the other, since it does work nearly as well.

Q: My question is about the barbed wire. This is a little bit counter-intuitive for me; I would expect the wire to tear the bags. Does this happen?

A: While the barbed wire does occasionally snag the polypropylene material, is rarely tears it very much. The barbs help keep the wire in place and also help the bags from slipping relative to each other.

Q: I saw this in a video called "Making the Soweto Hospice with Volunteers" where they said that it was not necessary to use the barbed wire because of these rebar stakes. I decided to do it like this because it´s cheaper. I could not afford the barbed wire, but if you tell me thatIi definitely need the barbed wire I will try to get some money to buy it.

A: We post lots of videos and pages about many different earthbag projects just to give readers as much information as possible. Ultimately it is your choice to decide how you want to proceed. I would say that 99% of the earthbag projects that I know about have used barbed wire, partly because that is how Nader Khalili, the architect who first popularized this technique, did it. Using stakes does help stabilize the wall, but the wire is just a bit better I think, especially if there were ever an earthquake that affected the house.

Q: Should one use rebar reinforcement every 2 feet driven vertically through the bags.

A: This is not reallly necessary, except perhaps where you want to tie the wall into a bond beam.

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: 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 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: Is it possible to build an earthbag wall even if it has been soaked by rain? Will this have an effect?

A: It really depends on what the bags are filled with, how much effect this will have on the integrity of the wall. You certainly do want the wall to dry out eventually, so the best thing is to allow this to happen naturally, by providing a roof over it to keep off more rain, and by not putting anything over the bags that will keep them from drying out...but of course, you also want to keep the direct sunlight off the bags. Once the earthbags are thoroughly dry, then you can preserve them with a protective plaster.

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: 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 saw that there were precast concrete arches built, and then put atop, or adjacent to, filled sandbags to speed up the process. I couldn't tell if sandbags were then stacked over the precast arch or not.

A: I haven't seen this having been done, but it should work, although it would be pretty heavy if you wanted to remove it to use over again.

A: No, not really. You can build with earthbags with just a bit of knowledge, although it is good to start with small projects to gain experience before taking on larger projects.

A: The time to build this way depends on many factors, obviously...the size and experience of the work force, the availability of appropriate fill material, and the complexity of the project.

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'm looking into earthbags myself. How hard is the labor compared to strawbale?

A: As far as the labor of building with earthbags compared to strawbales goes, I imagine that a strawbale wall would go up faster, but then you are stuck with using other materials to make the roof. With earthbags, you have the flexibility of being able to create curved forms, including the roof, if you want. Both systems require an exterior and interior plaster, which would probably take about the same amount of labor. Straw bales are quite heavy, and must be lifted into place. Earthbags can be filled in place, so the lifting can be minimal. Also, if the bags are filled with crushed volcanic rock, as I did, then they are relatively light (about 35 lbs) and can be lifted easily.

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 saw your (excellent) pictorial on the Riceland dome. I live in Central Gulf Coast Florida- subtropical -and want to build an earthbag studio, as simply as possible. Wondering how long it took to erect the Riceland and how many people participating.

A: My wife and I basically completed the Riceland project to the point pictured in that description during one summer. We had a little help from friends, but mostly it was me, with my wife helping occasionally.

Q: I get the idea that using individual traditional sized sandbags is cheaper than buying the long continuous bag material from Cal Earth, or trying to get a manufacturer to produce the same product. Seems to me that if the material cost is less, the labor involved would be greater, thereby perhaps offsetting the benefit if you are hiring the labor?

A: Well, it all depends...yes the long tubular bagging does seem to be more expensive, although it really shouldn't be, since it is basically the raw material that is eventually made into bags. I think that CalEarth has had a very nice business of selling the tubing at a considerable profit. Individual bags can be filled and handled by a single person (as I did with most of the house that I built). The tubing really needs a team to handle the various aspects of getting the bagging filled and laid on the wall. So it is hard to compare labor-wise.

Would you suggest using the long continuous bags, or the short ones, if you were approaching this subject in relationship to building up a small team that could go into business building these structures?

There are advantages to each approach. A well-practiced team could build rather efficiently in either way I think. The logistics of continuously filling tubing is potentially awkward, but possible. I suspect that there is a slight advantage with the tubing in terms of eventual strength of the wall to resist seismic events, but this has not been proven.

I heard it mentioned in some of the Cal Earth material that the process could be mechanized.

Sure, there are various portable conveyors that could be employed to elevate and feed material into tubing, but this would require some very coordinated movements to keep the process rolling. With indivual bags, you can use automatic bag filling machines, as described at http://earthbagbuilding.com/articles/bagmachine.htm .

I assume this means using a concrete pump to fill the long continuous bags. Again, have you had any experience using a concrete pump to fill the bags? Do you think this is worth doing assuming that one had the concrete pump in hand?

A pump requires a slurry of material to use effectively, and such wet material can be problematic with eathbag building, since it slumps and weaps, etc. It is easy to imagine some nightmarish scenerios with this...

It also seems that some type of stucco gun would be desirous if one wanted to cut down on the labor and speed the process up of putting the finished material on the interior and exterior of the walls. What do you think of using a stucco gun?

There is one particular type of stucco sprayer that will spray practically anything that is put in the hopper, including earthen plaster and lime plaster: TirolessaUSA Stucco Sprayer (available from Amazon.com).

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.

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.