Cob inside ICF?

Hello all, I signed up specifically to ask the following question to anyone who might be able to give advice.

I would like to know if placing cob (in my case I would be using a clay road base mix with added straw), inside ICF would create an adequate load bearing structure?

The cob thickness would be around 100 mm. Now surely that is far too thin if it was free formed, but what about the permanent moulding of the ICF to keep it stable?



Nathan.

Cob wouldn't be my first thought, no. I would look at something whose material properties are better known under tension and compression.

You have the clay road road base mix. Why not make up a dry rammed earth mix and ram that down into the forms? If you add about 5% portland cement or equivalent for stability, it should do exactly what you're looking for.

-CK

I would recommend the same as Chris. This is very similar to what I used. Built foundation with 2 wide ICF blocks, put up plywood forms to create 400mm thick wall. then did a rammed earth on that. Used a 3 to 5 % dry cement mixed with clay and sand. Slightly damped. Ended up with a 4 ' high rammed earth wall. This was all below grade. Then built aprox. 3' high cob on top of that. I did use vertical rebar between the rammed earth and cob.