In a recent thread, and I think it was related to dealing with humidity control in a full ICF home, someone mentioned that ICF is still giving off moisture for close to a year after install.

In my own full ICF build (in southern Saskatchewan) I noticed the concrete was still "green" and damp under the foam when I was cutting in a kitchen sink plumbing chase.  Main floor walls poured Sept 30, 2011 and plumbing done end of Feb, 2012 (5 months of curing).  House had heat but temp kept just above freezing and almost fully restricted to basement area using a plywood hatch to cover stairwell opening.

While responding to a customer question about mold issues with ICF, and I mentioned the above characteristic, he asked how long the moisture was a significant issue and thus how long to wait before installing drywall.  It sounded like a valid bit of knowledge to impart to customers so I'm tossing this out for comment.

I expect there are a number of factors that might alter a "magic time frame before drywall install" including time of year when poured, average temperatures and humidity, whether it is a foundation only or full ICF, presence of a sealed foundation floor and possibly more. 

Your comments would be appreciated.

Why would you want drywall when the superior ICF coating is PlasterMax for interior and StuccoMax for exterior?
No issues with mold/moisture, quicker to install than drywall and is fire rated and abuse resistant?
Happy to send you a sample if you have never seen it.

My 6" ICF walls, poured in August, 2011 were substantially dry by the end of December, 2011. It was a cold, wet winter in the Pacific Northwest and I tried to keep heat above 40F inside. Somewhere in December I noticed that the treated window bucks had stopped warping, were dry and had returned to normal. Holes drilled in walls and slab in January were dry and well cured.

To put a time frame on it, I'd say 4-5 months.

Posted By ICFcoatings on 19 Mar 2012 11:20 AM
Why would you want drywall when the superior ICF coating is PlasterMax for interior and StuccoMax for exterior?
No issues with mold/moisture, quicker to install than drywall and is fire rated and abuse resistant?
Happy to send you a sample if you have never seen it.

I appreciate the alternate suggestion and I am aware of the product.  While I couldn't put any substantiated number to it, I expect that at least 90% of homes in N America have a drywall interior finish. 

Besides, the customer asked about applying DRYWALL so I am simply trying to answer his question about THAT specific product.

not to mention a lot more expensive vs gyp. it may be quicker, but the labor savings certainly haven't proven to be of any benefit in my estimates.

The heat of hydration reaction will continue for many many years but it is over for all practical purposes after 60 days at that point (<1-2% water content) concrete is not "giving off" any moisture. That remaining water is trapped and will continue being consumed by the chemical reaction inside the concrete to bond with silicates (on going heat of hydration).

I didnt chime in on that other thread but generally the water content of wood is so high that it is more likely the source. Remember even kiln dried wood still has in excess of 10% water content. Regards.

ICF homes have initial high humidity because they are very tight. They are very often overtonned (a/c) - you need a small enough a/c (here typically 1000 sqft per ton) for the a/c to run long enough to reach dehumidification cycle.

Good post texas!

Could you be dealing with condensation? If the concrete is cold, because you haven't been heating the building that much, and you get a warm day with dew points higher than the concrete temperature, plus some air movement, you'll get condensation on the concrete. The condensation doesn't even have to be right behind the foam. When the concrete cures and shrinks, it'll leave a small space between the foam and the concrete, which can work as a drainage plane.

Regarding plastermax and such, don't you still have to sheetrock all the interior walls? You'll have to have something to adhere the coating to.

PlasterMax bonds to the EPS foam or can be applied to sheetrock directly. It is near impossible to dent/put a hole into. When doing ICF most people want the best materials, ones with no VOC, no mold etc. PlasterMax has been applied in correctional, military, hotels etc as it is so abuse resistant.

This is why you should pour the lowest slump possible and use a water reducer to increase the flow. not water

ICF as we all know is the perfect cure environment for concrete it keeps the concrete hydrated the longest give the best cure possible. The ICF itself as almost zero permeability to moisture. Drywall when needed.

All Sask - As Tex mentioned the concrete continues to hydrate for a long time inside the foam. And yes there will be a time when there is some excess moisture. If you don't put a vapour barrier on the ICF prior to placing the drywall, the drywall will be permeable enough to allow that vapour to past to the inside of the house with out causing any issues. Especially on the prairies. If you for some reason put a v.b. on the inside it will protect the drywall and force the moisture to the outside. I would keep the heat and ventilation at appropriate levels for the first 12 months and then I don't see any problems with the moisture.