Stabilizing Red Clay?

Hi, does anyone have experience stabilizing the type of red clay soil found in my area? I live in western North Carolina, in Madison County, northwest of Asheville. The soil here is a crumbly red clay from weathered amphibolite/hornblende gneiss. It has a lot of mica flecks and fine sand that does not readily separate much from the clay (using the “jar test”).. maybe 20% clay, 40% very fine sand and 40% less fine but still pretty darn fine sand. Wetted and squeezed into a ball it compacts well and holds its shape, but gets crumbly once dry. The soil survey says it gets sandier and more gravelly as I dig down.. so maybe upon excavating I will find some more suitable courser material. In any case, I am thinking it is still a good candidate for building! There are still examples of 100+ year old cabins that used it for chinking and other houses with red clay handmade bricks. But it could possibly benefit from amendments with course sand and/or lime. I am trying to balance the amendments cost versus their benefit. Does anyone have experience with this type of dirt or can suggest a good course of action? I do not have any poly bags to experiment with, yet.. that will be the next step. Also, this project is for the foundation wall of an earth-sheltered greenhouse that will be dug 9' into a slope. The wall has to be straight, but I plan on buttressing it every 7 ft and the ends will be quarter-circle curves 6' in diameter.

One more question-- is there a better (cost effective and effective) alternative to rigid insulation boards in my area? Can't find scoria/pumice/etc.. but there might be something I am not thinking of

Daniel Bowman : Spent some time near Martinsville and Pilot Mountain, and have lots of pictures of 100+ year old log and split rail Cabins chinked with your red clay
some in excellent shape though mostly used now as outbuildings !
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It sounds like you may have a little silt in with your clay, it takes a good ''Millers Thumb'' to tell Clay from rock flour, from From silt and other organics, I still get
fooled by my local babyshit yellow clay/slit and quit digging before I get down to the good stuff!

They tell the old joke about ''good clean, weed free oats will go for a premium price, if you want it after it has been through the house, you can get a good discount''!

The 'Road apples that have been through the house is probably the most common amendment due to certain enzymes and the pretty uniform length of the remaining
grass structure that is almost universally all a good length for a reinforcement ! Of course coarse sand will help too!

I can recommend a good book on the subject the hand-built house By Ianto Evans, the Rocket Mass Heater Wizard ! you can see if your lending library
can get it for you, or second hand thru Amazon books, Or to support the people that made this open information Cobcottage.com

Usually the clay structure sits on top of a foundation of stone laid down below your frost line, well drained sloping down and out to daylight and high enough to be
covered by the buildings Ample eaves. The expression for this is good high boots and a good (wide rimmed ) hat !

A finishing protective layer should be applied over your Structural Cob, but it will certainly need yearly refreshment if it must stand up to driven rain or water that can
splash up on it !

I have to quit here or show that most of my Structural cob experience is second hand. or related to a finish coat on a Rocket Mass Heaters Shell and thermal mass!

Other Fellow members will help you carry on From here ! For the Good of the Crafts! Big AL

Hey thanks. I was confused when you started talking about apples n oats until I realized you are thinking cob. But.. I wanna bag it! In any case, you are probably right if I go a little lower I will get out of the silt zone. I am invigorated to dig a little deeper! Incidentally, I moved here from Willamette Valley, OR and am familiar with Ianto's book. Good stuff. But let's talk earth in bags! Much more sturcturally stable when you have to account for underground pressures of lateral thrust and hillside creep.

I confused? If you are "bagging it" there is no reason to stabilize anything. Many (most) are just sand filled bags. So if all you have is silting clay...then use it, and build accordingly with the current "bag architecture" technology as it is. If trying to achieve another design other than bag...then you must use clay...as silt just does not work for most of the cobb, RE, and related modalities.

Regards,

j

Daniel and Jay : Sorry The confusion was all in my mind ! It wanders, fortunately it is to small to go very far ! Big AL

Re: Jay

Have you read the definitive "Earthbag Building" book? They recommend stabilizing any dirt that does not have the proper 20:80 clay to well graded sand ratio.

Re: Allen

Upon deeper shovel excavations I have found more sand but also more silt. I am thinking of redrafting my design with concrete again. Sigh.

I went down your same trail of tears. I came to the conclusion that to stabilize my soil I would use more cement than to simply build with concrete block (because of the thickness/mass of the wall). It was a crushing realization--but then that is why there weren't adobe buildings in my area in the past! Learning from history is important, as many of us in our exuberance fail due diligence for the appropriateness of our solution.

I am now researching the cost of building a solid block retaining wall with a precast block system of some sort. Not sure of the materials cost, but it goes from the labor-intensive extreme of earthbags to the build it solo in a weekend approach. If it seems feasible, the plan would be to secretly utilize the wall as the foundation for my lightweight wood-framed greenhouse later.

Have you read the definitive "Earthbag Building" book? They recommend stabilizing any dirt that does not have the proper 20:80 clay to well graded sand ratio.

I do recall this, yet believe if you research it that this is a "recommendation" not a requirement. I have seen just plan bagged sand work quite well, yet I have never been supper found of this architectural form above grade. I don't care for the "Cement Industry" at all, as most of there practices are the opposite of permaculture. You could use lime as a stabilizer or one of the enzymic soil additives used in road construction, yet I think you will find that the land will probably yield something more cost effective perhaps...

Daniel,

We live in your area and know some folks in the county who are also experimenting with earth bags. Let me know if you want to connect with them or chat in general about the area. Its great to meet more permaculture folk in the area.

Jason