# gap beneath sill plate



## mid-rise9 (Jan 4, 2013)

Don't know if this is the right forum for this question, this seems to be the best place for it. 

In my basement I have gaps between the top of the foundation and the sill plate, in some places the gap is more than 1/4". It looks like these gaps were partially filled with concrete in some places when the house was built in 1984. I also have concrete chipped off in some places which make quite large holes. We have mice getting in the basement - it might be because of this.

My first thought is to fill in the gaps with 2 options:

1) Fill the gaps with mortar (as was partially already done when the house was built). But I'll have wood resting on concrete - and I think moisture from the concrete might keep the wood moist - something you're supposed to avoid.

or

2) Fill with Great Stuff Pestblock foam. But we're having problems with water coming in near the bottom of the outside walls/siding in some places (a whole separate issue to be fixed later) so my concern is that expanding foam underneath the sill plate will prevent any moisture in the sill plate from drying out - making any possible moisture problems around/above the sill plate worse.

Any thoughts about the best thing to do?


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## Bud9051 (Nov 11, 2015)

IMO, mortar does not serve well as a caulking. I would clean off the excess and fill the gap with a silicon sealant. Where there are holes large enough for mice you could cover the top of the foundation with a layer of moisture blocking material and then fill the hole above with something that will block the critters.

In a cold climate there is considerable air leakage under and through that rim area. Lots of caulking is usually beneficial.

Water and moisture issues do need attention and often start with ground work outside. But a different topic as you said.

Bud


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