We are soon to start setting up ICFs for our basement foundation that will have both 6” and 8” thick walls 9’ tall.  We will be doing a monopour.  I have contacted two ready mix suppliers and one recommends their ‘standard’ 3000 psi mix for $96 a yard and the other insists their special ICF formulated (has some admixture to improve flow) pea gravel mix at $118/yard.  The concrete pumper contractor did not seem to care which one we used, but cautioned that with our monopour and the gap between the form and the bottom of the ICFs varying from ¾” to 2-3/4”, the larger aggregate is more desirable.  The concrete pumper has not done a lot of ICF jobs. 

With 33 yards of concrete, the difference between the cost of the two is significant enough that I’m inclined toward the lesser cost mix.  Any advice?

Thanks all for some good advice.

Paul, your right about the webbing – I was visualizing just the rebar, and there is a whole lot more complication in an ICF’s cavity compared with a standard formed concrete wall. We will go with the pea gravel mix.  I was contacted by the $118 concrete supplier’s salesperson, and they said they’d provide the ICF mix at $98/yd + $26 fuel surcharge on three trucks.  They seemed eager to get my business, but he also has been supplying concrete for the pump guy for many years. 

Chris, there is an engineer, but he had no opinion on aggregate.  He only cautioned that we place the concrete in small lifts and don’t fill from one point -- basic stuff that concrete pump guy already told me he does as standard practice. 

Renangle, we will put a set accelerator in the first truck pour.  Thanks. 

As to the lack of ICF experience: definitely lacking.  Though I have done a lot of formwork and pours on shorter stem wall monopours over the years.  Mostly though, I rely on experienced professionals to do the stuff they are best at – in this case it’s why we’ve hired the engineer, concrete pumper, flatwork contractor, etc.  The ICFs are new to me, so I attended a four hour workshop provided by the distributer, and I feel very confident that things will work out well.   I’m using the ICFs for two reasons.  The first is to provide an energy saving foundation for my home.  The second is, as a residential home designer, I want to promote the advantages of ICF usage, and there is nothing better than walking the talk.