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What other materials have you tried?  RSS feed

 
Helen Gilson
Posts: 38
Location: Zone 6 Ohio but interested in Zone 6 Southwest
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What other cob ingredients have you tried? I'm thinking recyclables. Can you use shredded cardboard? Dead leaves? What about shred tires? Must it be able to absorb moisture? Does the straw work best because it stays stiff-ish when wet? I saw one post testing pine needles. What about brush, tumble weeds, mesquite, etc

Also in the whole clay/sand mix, where would Caliche fall as an ingredient? It's a southwest soil type so it must have been prevalent in old time adobe bricks, right?

We are looking for small test projects to do but we live in Ohio now and our eventual large project will be in Arizona, so thinking ahead to available materials.

Kinda rambling but anyone with a minute to respond or just point out other good threads in the forum is appreciated. I'm reading "Difference between Cob and Adobe?" and "cob building - when clay isn't clay" as they seem to have good info. Reading very free pdf on cob building I can find. Pinterest and Facebook following Cob architecture. Most of them are so fantastic and involved they make it more intimidating but always intriguing.


 
Peter Ellis
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Location: Central New Jersey
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Helen Gilson wrote:What other cob ingredients have you tried? I'm thinking recyclables. Can you use shredded cardboard? Dead leaves? What about shred tires? Must it be able to absorb moisture? Does the straw work best because it stays stiff-ish when wet? I saw one post testing pine needles. What about brush, tumble weeds, mesquite, etc

Also in the whole clay/sand mix, where would Caliche fall as an ingredient? It's a southwest soil type so it must have been prevalent in old time adobe bricks, right?

We are looking for small test projects to do but we live in Ohio now and our eventual large project will be in Arizona, so thinking ahead to available materials.

Kinda rambling but anyone with a minute to respond or just point out other good threads in the forum is appreciated. I'm reading "Difference between Cob and Adobe?" and "cob building - when clay isn't clay" as they seem to have good info. Reading very free pdf on cob building I can find. Pinterest and Facebook following Cob architecture. Most of them are so fantastic and involved they make it more intimidating but always intriguing.


Caliche is defined as a calcium carbonate based sedimentary rock, but also as a calcium carbonate based accretion of sand and clay. Neither fish nor fowl, it seems unlikely to work in traditional cob. OTOH, it is the result of Calcium carbonate cementing the particles together, so there may be some method of taking advantage of that cementitious quality. I don't know whether there is any vernacular architecture that used it or any modern work exploring it. Considering it is a fairly common AZ occurrence, might be worth some research.

Shredded rubber in cob - I cannot imagine that producing any kind of good results. The clay won't adhere to the rubber, the rubber is impervious to moisture which again serves to separate it from the rest of the cob matrix. And there is the whole issue of introducing something that has potential to off gas toxic fumes into what would normally be a really healthy construction method.

I would not go with shredded cardboard for cob, but look into papercrete for an example of using cardboard and paper to produce a lighter weight and better insulating concrete, using recycled materials. The reason not to use shredded cardboard in cob is that when wet cardboard has no integrity, no strength.

Straw is used not because it stays stiff, but because it retains its tensile strength. Pull on the ends of a wet piece of straw, it is just as strong as it was when dry. Try that with a cardboard ribbon

Shredded leaves are not a good idea for cob either, again because they provide no strength.

The reason straw is used is to introduce additional tensile strength to the matrix. You want something that has tensile strength when wet, is somewhat flexible, and that the clay will adhere to well. Some other traditional materials include horsehair. Probably any sort of hair would work.
You don't want to be incorporating sticks, too brittle and creating larger voids in the clay sand mix than are desirable. Something like bindweed, a slender, tough vine, might make a good ingredient.
 
Jami McBride
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Peter has pretty much covered it

I would add : reeds - those with long strong fibers. And sticks, placed here and there, as long as they are not thin and brittle as mentioned. You can even place these closer to the interior to have anchors for hanging pictures. Likewise raw wood chips, not landscape chips, have been successfully added to cob for anchoring wall cabinets in a kitchen - cool. As Peter mentioned anything with tensile strength, no matter how short and small will work. But straw is especially good for this purpose.
 
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