Frequently Asked Questions
Frequently Asked Questions About Earthbags
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?
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.
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?
I would imagine that using Polypropylene would not be very 'green' because it is a 'plastic'; how can your building be properly 'breathable'?
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.
What is the ideal width of an earthbag wall or the recommended dimensions of the bags for this application?
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)?
I live in Arizona; where is a good place to purchase polypropylene earthbags for building?
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.
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).
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.
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?
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.
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?
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 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.
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.
“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.
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.
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.
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.
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.
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?
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.
What size width tube role I should use?
For a wall are individual bags better or should we use long runs of tubes?
Is it possible to find the continuous superadobe fabric tubing or is it better to use individual sandbags?
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?
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.
How would I locate used bags?
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?
If a house is built of sand filled plastic bags, will the moisture trapped in the bags cause mold?
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?
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.
How thick is the typical wall? Does this differ for outer and inner walls?
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.
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?
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.
The use of a bag full of whatever to start off a home makes no sense at all; the bag will disintegrate.
How long will earthbags hold up in sunlight?
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.
Do plastic earthbag bags off-gas fumes like VOCs, etc.?
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.