I make infield mixes for baseball diamonds and after doing research on making cob the ratios of sand to clay are pretty close.
Cost for a pre mixed infield mix runs from 20 to 50 dollars per ton (one ton is 1.35 yards) plus shipping. A typical load is about
25 tons which would make a wall 1' wide x 8 tall' x 60' long and cost 500 to 1250. Usually they will sell trailer or pickup loads depending on location.
If a person went this way you would need to ask for the tests on the mix for
the actual ratio of sand to clay and also the silt to clay ratio. Most clays in the midwest I work with are a 1 to 1 silt to clay.
Some times the silt to clay ratio is deceiving as silt gets finer toward the coarser clays it performs almost identical, so a sample from
their pile and how it sets up would be wise.
I have brought some straight clay and mix home to experiment this winter with a rocket stove
Billy Larson : Welcome to Permies.com / Richsoil.com,and a Big Welcome to The Rocket and Wood Stove and Cob Forum Threads. With 28,000 + Fellow Members
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The % of stilt you are reporting sounds high for good Cob. But I will just mention a couple of three books that you might find useful, There is The Brand
New 3rd Edition of Rocket Mass Heaters, Which is available as a downloaded PDF From Cobcotage.com , the two best books for learning to work with cob
are The Hand-Sculpted House Ianto Evans Et Al, and The Cobblers Companion, Micheal G. Smith founding director go Cob Cottage Co. The last two are long in print and you
may be able to get them through your library or From Amazon Books, or from Alibris Books, and good used books or from cob Cottage who after all started the whole
thing here in America!
Regardless Please let us know how your winter project goes !
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posted 4 years ago
I work with natural clay in illinois, wisconsin, michigan at several locations in each of these states. Unless it is a grey color fire clay it is very hard to find a silt to clay ratio where the clay is more than 50 percent give or take. Most of the time the silt percentage is higher than the clay and in reality what most people are calling clay is actually silt. So a typical mix is 70 percent sand 15 percent silt and 15 percent clay.
The sand we use is usually not considered coarse or fine but a medium gradation. To fine of sand will lend towards the silty and too coarse more like a concrete.
I will let you know as I progress this winter when I get home, making mix in Texas right now and maybe Oklahoma next....make a pretty red cob
I am under the assumption that at minimum you have drawn your conclusion about “silt to clay” rations from a thorough “shake test” of your different samples and/or microscopy sample examination. In my experience, if the mineral soils the samples come from are yielding any clay veins, the rations are much higher up to 98% pure clay. Colors range from reds and blues to whites and grays…many different colors.
For good cob and/or clay paints/plasters, you do not want any silt (or very little) if possible. Testing is of course the final step, as suggested, and these I would also subject to fire to see how they behave, as well as, “frame modeling” to see how the pull away, and to what percentage.
Good luck with your search and testing.
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