Replies

1. 
   onslow | Apr 01, 2018 04:39pm | #1

   Are you sure where the air is coming in to the edge slab? Depending on the ICF pour and the current level of finish on the wall, both inside and out, the actual source could be from window or door openings tracking down to or along the slab edge. Alternatively, the slab is presumably insulated and a stone layer is under that. If the interior stone is drained to the outside under the footings, I would go plug the drain pipe and see if that helps. If you have a radon piping system under the slab which is already connected to the outside air with a stack pipe you will need to plug that as well.

   If the wall pour resulted in gaps from not being properly vibrated, you might be able to pull air directly through the block intersections. If you have set interior wall finishes, the air might be slipping in around window bucks on the under side. I assume the windows are in and sealed to the bucks, but has the concrete shrunk away from the bucks. The ICF might look tight yet still allow air infiltration. If the interior walls are in place the air will appear at the bottom edge.

   I personally loath silicone for all most all uses. The surfaces must be very clean and one thing concrete is not is clean. The paintable silicones are an improvement and at least they allow more caulk of the same type to be applied when it fails on one or the other surface. Given the crumbly nature of foam blocks I would suggest the pourable patio crack filler that is water based made by Quickrete. It is not approved for radon protection, but it will not dissolve your block and it will stick to concrete. There are other concrete sealants which are much bigger chemical risks along with much better performance characteristics. I don't want to get into a big go around on their merits.

   The Quickrete does pretty well outside in sun and water so I suspect it will do much better inside. Don't forget the backer rod along the gap and fill at least 3/8 to 1/2" deep. Best of luck hunting for the source of the air.

2. 
   Trevor_Lambert | Apr 02, 2018 08:55am | #2

   We used this stuff on all the seams in our house, including concrete floor to OSB interior sheathing:
   3M 8067 All Weather Flashing Tape
   You can get it in various widths from the place where rain forests grow. Similar performance and much cheaper than euro sealing tapes (e.g. Siga), is what I was told. What I can say from experience is that it does stick like crazy to just about anything other than loose dirt/sand.

3. Expert Member
   Dana Dorsett | Apr 02, 2018 12:00pm | #3

   Soil is porous. The washed gravel over which slabs should be poured even more so. No amount of air sealing the exterior of the ICF will seal the air leak between the slab & interior side EPS- it has to be sealed on the interior side. It's very common for slabs to leak at the slab-foundation wall boundary even without the intervening EPS layer (a fact well known to radon mitigation contractors.) With the EPS it's even leakier, due to the seams in the EPS.

   Silcone caulk would be the wrong material, with fairly poor adhesion to EPS and will likely fail with seasonal dimensional changes of the slab with temperature. Polyurethane caulk formulated for concrete sticks pretty well to both, and remains flexible over time. It is likely to need tape or caulk at the seams of the EPS too.

4. 
   calum_wilde | Apr 02, 2018 01:35pm | #4

   Dana, as always, you have the right if it. That is exactly the air leak issue I'm trying to fix, from the interior.

   Thank you for the product recommendations.