Waterproofing foundation
I have a 100 year old triple brick house with a brick foundation. I replaced the foundation on 2 sides with poured concrete. The house is semi-detached so I am attached on one side and the back wall is still brick, but it has been repointed since it was quite small.
The company installed a french drain with sump pump and the joists are embedded in the new poured concrete wall, but they were wrapped with blue skin before so the wood is not in direct contact with the concrete.
On the outside, the put a foundation coating, but no dimple mat. Foundation walls are 12″ thick. I read a lot and it seems dimple mat is best practice, but not always necessary. I’m worried about a crack in the future and water seeping into the basement since I will be finishing the basement later this year.
I will also be insulating the basement with 3″ of spray foam for an R-21 and spraying inside the rim joist cavity. Even though the joists are embedded, I believe the potential ‘rot’ issue is negated by the blue skin and I will be installing a 2×4 walls 2″ in front of the concrete to support the joists and run electrical, etc.
A lot of different points are touched on in different articles on this site. I’ve read them all. I believe interior spray foam with protected joists (wrapped) and a stud wall is correct and while the foundation walls would be better served with a dimple mat, I am loathed to excavate again to install one. Is the coating sufficient for a 12″ thick wall? Should I install an interior dimple mat?
Thanks,
Jason
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Replies
I would probably assume that the exterior coating will handle most of the groundwater and add a dimple mat on the interior before spray-foaming to handle any water that still gets through the wall, leading to an interior perimeter drain that goes to a sump pit with pump, or to open air. If it's only a small amount of water, the tiny spaces between the foam and the foundation will provide enough of a drainage plane, but a dimple mat is more reliable.
Do you mean Henry Blueskin VP100? That is a vapor-permeable product and won't protect your joists from moisture, only liquid water. I believe there are also Blueskin products that are vapor impermeable so whether your assembly is safe really depends on which product you heave.
Thank you for the reply and your comments. I can't really do an interior dimple mat with a drain because I poured a fresh slab with in slab heating so I guess my question boils down to is the coating enough or should I re-excavate and add the dimple mat. I have an exterior drain connected to a sump pump.
I believe the product used was the Blueskin WB Air and Moisture Barrier. Regardless, I will have a stud wall supporting the embedded joists.
Thanks,
Jason
No system is 100% reliable. When it's critically important to keep water out of basements, I include at least two water management systems. In your case, both would have to be on the exterior. In other words, I would consider adding a dimple mat to the exterior.
Thank you!