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Backyard recipe for making cob  RSS feed

 
Oliver Stanton
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Good day to everyone! First post here at Permies.com and posting from englewood, CO. Working fast for a life change that continues to make me happy, self sufficient living.

One of the cornerstones to that education is COB. I have learned a lot from ernie & erica, forums, youtube, google, and forums again. Still I have trouble either cleaning my head and overanalyzing how to make cob from clay dirt in my backyard or I am just not finding a general guideline specific enough to my brain to fully understand how to make cob from clay I dig up from 18" down in my backyard.

I'm looking for that magical thread that explains A RECIPE ON HOW TO MAKE COB FROM DIRT GATHERED FROM MY BACKYARD (Or recipe for making cob from clay/dirt extracted from the ground. Need some guidance as all dirt has different compositions and as a newbie I am having trouble looking at dirt and saying "this needs more sand OR this needs more clay OR this needs more dirt from my backyard, etc). Some particulars include:
1) Testing dirt with a layer test in a mason jar (having trouble reading my results but will try again)
2) how to treat or prepare my dirt for making cob (do i have to let the clay dirt dry then crush it and remix then strain? OR do I have to let it sit in water for a month? OR do i have to treat the clay dirt at all besides getting out the organic matter, rocks, roots, etc?)

What I have done:
1) Soil tests include:
a) putting soil from 18" down into a jar, mixing heavily, letting sit. Marking sand @ 1 min, silt @ 1 hr, clay when water is clear. Still waiting but think I did it wrong.
b) Snake test: rolled clay soil from ground into a snake then a donut. Added about 10 drops of water to golf ball sized clay. Some sticking to hands as clay, some silt on hands (dries quickly and rubs off), but the snake did not go even a quarter of the way around my finder.
c) Drop a ball of clay dirt from 5': Breaks apart into several clumps dry and fewer clumps with 10 drops of water.

I live by red rocks amphitheater and could look into getting clay from there. Still learning and would love to take it out of my backyard if possible. If there is already a thread that covers these questions and you know where it is then send me a link. Any help is much appreciated by this curious, hardworking homesteading newbie.
 
Miles Flansburg
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Howdy Oliver welcome to permies!
Maybe this one will help?

http://www.permies.com/t/16233/cob/Making-cob-basics-basics
 
leila hamaya
pollinator
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Location: northern northern california
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Still I have trouble either cleaning my head and overanalyzing how to make cob from clay dirt in my backyard or I am just not finding a general guideline specific enough to my brain to fully understand how to make cob from clay I dig up from 18" down in my backyard.

I'm looking for that magical thread that explains A RECIPE ON HOW TO MAKE COB FROM DIRT GATHERED FROM MY BACKYARD (Or recipe for making cob from clay/dirt extracted from the ground. Need some guidance as all dirt has different compositions and as a newbie I am having trouble looking at dirt and saying "this needs more sand OR this needs more clay OR this needs more dirt from my backyard, etc). Some particulars include:
1) Testing dirt with a layer test in a mason jar (having trouble reading my results but will try again)
2) how to treat or prepare my dirt for making cob (do i have to let the clay dirt dry then crush it and remix then strain? OR do I have to let it sit in water for a month? OR do i have to treat the clay dirt at all besides getting out the organic matter, rocks, roots, etc?)


yes, over analyzing, me thinks.
it's more of hands on learnt skill, you have to experiment and make mistakes, until you grok it =)

and find a good mix, with the specific materials you are using, because as you were saying they are all different, the dirt has very very different properties in different areas.
i have never been there, but from brief conversations with some people i know in CO, the dirt is really weird, very unusual conditions and they have to add so much to get any food growing beds.

heres a really general recipe, a place to start

2-4 buckets of sand, 1 bucket of screened clay dirt, 1/2- 1 bucket of straw

but recipes cant really be exact, and theres a huge amount of different recipes to experiment with....

then theres a whole assortment of other things you can add in and try out different recipes with- like builders clay from the hardware store, lime, manure (weird, maybe, but its chewed up straw basically), sawdust, woodchips, etc etc etc. other related building methods, like making bricks and forms, which is more what i prefer.

a method i have used most often to process the subsoil clay dirt = get a bunch of containers, buckets and especially large plastic tubs and put hardware cloth, or a metal screen of some kind with large holes, on top of it. dig the clay and throw it on top of these, then use the hose to wash it through the screen. this takes out large rocks and clumps, also roots and such organic material.
now your clay is too wet for using immediately, let it dry out slowly (and naturally stratifying by weight in the tubs/buckets) and keep pouring off the top water as it settles every day or so.

you can pour off a larger amount into other containers to separate it.....as the top will be the lighter particles, more of "slip" clay, and the bottom will be the heaviest.

but of course, theres a million other ways to do it, a bazillion recipes that work depending on the materials, so experiment with something that works for you.
 
Peter Ellis
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Location: Central New Jersey
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I am no expert, but I think it is safe to say that no expert could give you a recipe that will work on your property without coming to your property and checking out your land. They would need to experiment a bit with the material on your land to figure out the recipe for your specific raw materials. They would be able to figure it out pretty quickly because they have done it many times.

I have made a couple of cob structures, in a couple of places. My property has pure sand, no clay and no silt, just sand. I have to bring in clay and do a mix and add and mix some more in order to get to a good mix. Another site I have built on has good soil, a nice mix of sand and silt and clay and organic matter. There I needed to find a clay deposit to raise the clay percentage a bit and bring in some sand to get the mix to a good point.

In other words, it takes messing around and figuring out what your mix needs to achieve the right balance and then adding some of that until it starts behaving he way you want.

Practice, it really is all about practice.
 
Oliver Stanton
Posts: 9
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All great information! Thank you! I'm trying to experiment without screwing up my rocket mass heater riser tube. Will anything go wrong if I get my mix incorrect, fill my riser tube, and start a fire?

Will heavens fall, will bombs explode? OR will my fire SIMPLY be less efficient & less sturdy until I get my cob mix correct?

I just want to dig down 18" or so, pull out what is hopefully clay dirt (sift it, mix with water, dry, smash with hammer, mix with water then make cob) & make cob for my rocket mass heater!
 
Peter Ellis
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Location: Central New Jersey
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I would not say bombs would fall. What may happen is that your cob will crumble and break down, eventually collapsing. I made the feed tube and burn tunnel for my first rmh using rammed earth and it is breaking down and will need to be rebuilt. Not enough clay in my mix.
 
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