Excuse my ignorance, but when I first heard about these, I was told they were formed up so far, poured, and then built up some more and poured, etc.  From my understanding of concrete, doesn' t this create cold joints in the walls?  And are these a problem?

Chad,

The usual method of pouring ICF buildings is floor by floor but there are circumstances that will dictate a variance from this method. You are absolutely correct this causes a cold joint. This is not a problem for strength nor in above grade walls your cold joints will be transected by rebar. Remember concrete has great compressive strength but poor tensile strength, that is why you use rebar with concrete because it has great tensile strength. The only issue with a cold joint is in a below grade application where this could be a potential place for water intrusion.

ICF Contractor

When building your ICF wall most of us build the height of the first level, and we pour that wall in 4' lifts all on the same day. The concrete in the wall already will still be wet and the new concrete moisture along with consolidation will create a bond at that seam. If you do pour on seperate days there is a solution called binder mix that your concrete supplier can bring to your site and mix up in 5 gal pails this gets poured in at the begining of the new pour and is pushed around the wall by the new concrete solution being placed, although it does not add much strength it will seal the cold joint.

I agree with ICF Contractor in regards to the compressive strength of concrete and the tensile strength of rebar.