GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter X Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Insulated Concrete Form (ICF) Foundation Drying Potential

qofmiwok | Posted in General Questions on

Can someone explain how the concrete in an ICF foundation block can dry when it is covered by a waterproofing membrane on the outside, and a tumescent paint on the inside (required by fire code)?  I haven’t found any tumescent paints yet which published perm ratings.

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. Expert Member
    NICK KEENAN | | #1

    Concrete doesn't need to dry. It's strongest if it stays wet. Build with the assumption that concrete walls can't dry and won't dry.

    That means a couple of things. Where wood meets concrete, it means a capillary break and pressure treated wood, which code requires anyway. There should be a vapor barrier between concrete and the interior. Any building material that touches the concrete should be impervious -- foam insulation, paperless drywall.

  2. jackofalltrades777 | | #2

    The concrete within an ICF (EPS of 2.5" x 2.5") will dry through the top/bottom and sides/horizontally, albeit slower due to the EPS. Concrete doesn't mind getting wet, as long as it's not salt water. In which case the rebar can rust and cause problems.

    Like it was mentioned, if concrete touches wood, a capillary break will work even if the wood is not pressure treated. Code here allows for untreated wood to be placed next to concrete as long as there is a capillary break. Also a good idea to keep water from the footings/foundation area, no matter what type of build it is, wood or concrete.

    Tests have been performed on ICF walls and the concrete cures slowly within the EPS sandwhich, which is ideal, and it increases the psi of the concrete. A poured 3,500 psi mix can see 4,000 or 4,500 psi cured strength after 30 days within an ICF wall. As the curing conditions within an ICF wall area ideal (no wind, thermally protected from heat/sun, slow curing times).

    1. qofmiwok | | #3

      I'm actually referring to ICF block foundation, not walls. So it's underground, with a waterproof membrane on the outside, tumescent paint on the inside (required), and a capillary break (I've even seen fluid applied membrane applied over the top of foundation walls.) Hard to see how it will ever dry.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |