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Poor soil for earthbag building??  RSS feed

 
M. A. Carey
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I did a search first, but didn't see my specific problem addressed. I am sorry if it has been addressed already and I just didn't find it.

I did the soil test with mason jar half filled with soil and half filled with water and shook it up quite a bit. Every day for three days I looked at it and there weren't any layers. There was mostly clear water on top with some floating debris, but only the one layer, so I don't know what kind of soil that I have. I live about halfway between Williams, AZ and the Grand Canyon, just 2 miles east of Highway 64, 2 miles south of Valle, AZ. I have been told that the soil is cinder soil, but I don't really know what that is, other than rocky soil. It is very dry here and the dirt looks cracked from the lack of rain. When it does rain, it dries very quickly. Is there some way I can find out the soil content? We want to build a rectangular earthbag building, 12' X 16'. My husband has no problem with paying to have dirt hauled in, but since the ratio of dirt is supposed to be about 20-25% clay and the rest coarse sand and small gravel, how will I know if what we buy and have hauled to us is going to be the right mix? We are poor people and want to spend what money we have wisely, so we want to make sure we are going to be building with the correct ratio of soil in our earthbags. I am reading the book Earthbag Building; The Tools, Tricks, and Techniques by Kaki Hunter. She claims the soil needs to be fairly damp; actually damper than what the natural clay to sand/rock ratio, so I am a little disheartened before we even begin. If anyone can help me with how to remedy poor soil once I find out what it needs, or our case, prefer to have soil brought to us--how would we know if correct ratio, I would appreciate any and all input.

Many thanks for this great informative forum.

Margo
 
Terry Ruth
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Margo, welcome! At what depth did you get the soil for your jar test?

Be careful what you read in books, nobody is such an expert that they have built with every soil in every climate zone and can advise accordingly.
 
M. A. Carey
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Hi, Terry. My husband had dug a large hole for composting and the dirt piled up from the hole was probably from the deepest part of the hole, which was about 4 feet down. All the dirt looked the same, but I know it was not from near the top before the hole was dug, since what I used in the soil test was at the top of the dirt pile, which was from the bottom of the pit. It could have been a bit shallower than 4 feet, but not much, just guessing.

We would probably be better off having the soil brought in, since it is extremely hard to dig in the earth on our property. I just want to make sure that we purchase and have delivered the correct type of soil. I assume the rock quarry or yard personnel would be able to tell us, but who knows if that would be the case. Some people would give you an answer even if it was only a guess. Do you know if there is some type of soil testing product I could purchase that would tell me the soil type? I know there are kits to tell you the pH of soils, but we just need to know the type of soil.

I may have been naively under the impression that you could use "any old dirt" for the soil for earthbags and thus so finally convinced my husband that we could do this. He now knows that this may not be the case and he is on board with having dirt delivered. But he, like me, wants to know that we are going to get what we need.

Thanks so much for reply.

Margo
 
Terry Ruth
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Margo, it be interesting to see your jar test of the site soil if you know how to post a pic. As far as soil type run this report below, it will also identify flood planes or look @ FEMAs latest: http://websoilsurvey.sc.egov.usda.gov/App/HomePage.htm Click "Start WSS" follow the prompts.

Whether it's earth bag, rammed earth, adobe brick, etc, the goal is to resist thermal conductivity (r-value) in part, not thermally bridge from the two surfaces (inner and outer). In addition, in wet/hot climate zones humidity/heat buffering that is a function of clay content. The aggregates provide more of the r-value, the clay is the "glue"or binder.

In your hot dry annual climate zone overheating from too much mass that slowly reacts to temp change of the south/west facing walls will be the biggest challenge. You will want to use low E/SHGC min. window areas and/or natural shading and low levels of heavy hygroscopic mass (clay), more insulation less dense aggregates would be better.

If you consider the bags as the insulation "core" of the wall assembly you do not need alot of clay especially in your silt/sand soils. I'd be more concerned about putting too much foundation bearing loads since it can only take ~ 1500 PSF (see attached). With that said, less dense light weight walls are better. So, any soil or light high r-value aggregate will do.

When it comes to the "skins" plaster/stucco now you need a good binding clay as a first "brown' coat base that sticks to the bags. Since your soil has low clay content it may need to be stabilized with portland cement or lime that is a stronger clue. High calcium lime would be a good start, or try Type S mortar that has magnesium in it, if not go to Portland cement. Would not hurt to bond the bags too.

I would hope the quarry has dug deeper and has a higher clay content but do go get a sample to jar test to verify that. If you want to see if your walls are exceeding 1500 PSF and can take the roof loads hire a PE. Settling and foundation issues are not pretty.

I know that may not agree with your book so I tried to provide technical reasoning. Any questions feel free to ask.
Soil-Compression-Allowable.JPG
[Thumbnail for Soil-Compression-Allowable.JPG]
 
Jj Grey
Posts: 12
Location: NORTH Great plains (spit wrong and hit Canada)
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Do what I have done- ask the local gravel company if you can have a sandbag or two full for testing first. If you come to them to pick it up they will probably be willing to let you apply shovel yourself and do so for free or nominal charge.
Take the bag(s), pound it, and test it as described in the books.
In my case I need sand and possibly fiber as my soil is almost 100% clay. It sets up hard easily, but fractures just as easily and a stuffed full bag can compact by 15% too.
 
M. A. Carey
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Thank you, both Terry and JJ. I already disposed of soil test so unless I do it again I won't have a picture of it. However, I did make up some cob bricks using 50/50 dirt and coarse sand, with some dry long grasses (didn't want to buy a bale of straw just for testing). I made 6 bricks. After about 6 hours my husband picked one up and dropped it and it broke/crumbled. I told him I wasn't ready to test them yet. He thought I used too much sand. So, I kept the other 5 bricks until I was going to have time to make test #2, which was a few days later. Before making up the next batch, I dropped one of the bricks from hip high and it didn't break. I dropped from chest high and it didn't break. Before trying shoulder high, I decided to drop it on a wooden floor instead of the ground and at chest high one corner broke off, maybe 1/2". So I wondered if they hadn't cured enough. I never did try the shoulder high drop though. I ended up soaking the remaining bricks in water and added more soil only; about 25% more than original mix and did not add any more sand, so now it was like 75/25 dirt to sand. They have been curing only for one day now and I will test them on Friday, the 17th.

At any rate, my husband is skeptical about the whole earthbag building. He is a carpenter by trade and knows about loads, and more than I could ever know. Right now I am filling plastic bottles with dirt and small gravel to make a firepit. Once I have enough bottles filled we will purchase some fine cement. My husband is digging a trench to lay a rubble foundation and we will use some rock mortared underneath the mortared filled bottles. If this holds up after a year (right now this is our summer home and Yuma is our winter home as we live in a 1992 motor home and dry camp here and on the BLM near Yuma) then we are thinking about an earthship building, but using bottles instead of tires. However, he will implement post and beam framework and we will fill walls with the soil-filled bottles.

I went to the websoil survey, but once I downloaded for my area nothing came up. I have to pay bills right now, but I will experiment with that website later on today or later in the week.

Once again, thank you both for your suggestions.

PS: I think maybe the soil here is mostly clay. When making the bricks, the cob mixture was easy to roll into a snake and wrap around my fingers.

Margo
 
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