Cordwood, Clay & Foundation?

[Sebratis]

If you were building a cordwood house in an area with 70' deep clay base, what kind of foundation would you choose?  Also, anyone who can tell me the concrete typically used in the construction of a cordwood house?

Thanks

[glenn kangiser]

Are you in an area that requires permits?  Is the clay expansive?  A different foundation is required where the clay expands greatly.  Usually an engineer would have to be consulted where expanding soil is a real problem.  

On one of my jobs we had to dig a perimeter footing about 3 feet deep around the entire building and reinforce it with rebar to seal the clay under the building and keep it dry so it wouldn't expand and break  the concrete.

The foundation concrete used is normal concrete - commonly referred to as 5 sack mix unless an engineer specs something different or you were doing it without permits and wanted to use something less which may or may not cause problems.  This type of foundation is pretty expensive due to the massive amount of concrete used so I would recommend that you research what is common in your area, what is approved if that applies, and what works well to keep costs down.

Rob Roy suggest the following for the mortar mix:

9 sand 3 soaked sawdust 3 lime 2 Portland cement.  This is used at each end of the de-barked, dry, softwood rounds with lime treated sawdust insulation in between the mortared outside ends.  There are a lot of things to consider if building this type of house and I would highly recommend getting his book and studying it well before starting.

It and other cordwood information is available at http://store.yahoo.com/dirtcheapbuilderbooks/corbuilstato.html

[Amanda_931]

70 feet deep clay?

I need some!

Yes on Rob Roy's books.  They got me interested in owner-building many years ago.  

Cordwood is absolutely gorgeous.  There's a house partly built of cordwood near here.  They did have problems with the wood (mostly red cedar, left to sit at least a year) splitting after it was put into the wall. (Invasion of the Asian Lady Beetles!)  So they concrete stuccoed over the outside, left the inside for us all to oooh and aaah over.

If you're in a termite area think about that as well.

[glenn-k]

I have 45 feet of clay- the nice hard only slightly expansive type that makes great cob, or rammed earth with sand added ore even great adobe if used by itself with straw.

Sebratis, you might check out the referral link on the India faced interlocking blocks or make some adobe too.  With that clay you could also do cob or the other walls mentioned above depending on building restrictions in your area and if you needed sand added.