Are there any spray foams or caulking which would be suitable for filling large gaps (0.5″ – 0.75″) between the top of a concrete foundation wall and a shimmed bottom plate?
Ideally, the material would provide insulating value and structural support, but not expand and lift the plate.
If not, how best to fill this gap?
Thanks
Bob
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Replies
Sounds like this would need to be something with a fair bit of compressive strength, no swell and no shrinkage, and stable with time. Sounds like low-shrinkage grout would be the tool for the job, but I'm not a concrete/masonry guy so take what I say with a grain of salt. It seems obvious that the structural integrity of what you're doing would be far more important than the thermal properties, so I think that foam would be out of the question.
I doubt you will find a filler that is structural in nature, at least not within any reasonable budget.
Forgetting that aspect, you could use foam 'caulk backer' rod or EPDM gasket on the outside, then fill with foam from the inside. Foam is no good exposed to sunlight.
Another option in to cover the gap with a trim board (widen existing water table trim board, if you have one), or flashing, then foam from inside. These options would probably look better. I think structures look nice with water table trim at the bottom anyways.
Is this new or existing construction?
If new I would use steel or PT shims under the bearing points and expanding foam for the infill.
Jon Blakemore
I agree. The load isn't evenly distributed, so shims where the load is will hold up the house. Foam or caulk will get rid of the gaps.
If the load really were evenly distributed on the mudsill, for most 1 and 2 story houses it probably works out to somewhere in the 10 to 40 psi range. Check the fine print on the foam tubes, cause you don't want it accidentally lifting the house.
-- J.S.
Ideally, the bearing wall - foundation wall - would be in continuous contact with the bottom plate to distribute load. In practice, many will shim at the low point of the wall and at the hold down points. A better way would be to shim on the same schedule as the studs. PT shims are common but could compress over time.I would use a cementious grout and pack it in good. It will shrink somewhat as it dries but will augment the shims and limit their compression. Note how high CMU walls go without having the mortar crumble out due to compression. Also makes it tougher for the little multi-legged critters to invade.
DryPak.
Pack it in from the outside, leaving a 1/4" deep channel. Caulk/fill the channel with Lexel.
Go back inside and pack it full. Don't pack it so tight that it lifgts the plate.
SamT
Non-shrinking grout. Available at the building materials store where the various ready-mix concrete, portland cement, and other cement products are sold in sacks. It's not cheap, about $15 for a 60# sack, but you can mix it up and pack it in under the sill. It won't provide any more--or less--insulation than the concrete it's sitting on top of. It's designed to be load bearing in situations exactly like you describe.
Edited 3/29/2004 9:27 pm ET by davidmeiland