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Community and Q&A

Sill sealer help please

Roger_S39 | Posted in General Questions on

Hi all,

Is there any benefit/need to put a foam sill sealer under interior bottom plate walls?

*** The question is in regards to a slab on grade foundation.

*Given an important reason for putting a foam sill sealer under the mudsill is for it to act as a capillary break, is it necessary / a good idea to put the foam sill sealer under all of the first floor bottom plates as they are all in contact with the slab?

*OrĀ  is it that the perimeter of the slab has a much higher moisture content and therefore only here the foam sill sealer is needed?

*If the perimeter is higher in moisture content levels, does that moisture travel horizontally inwards along/through the slab above any “plastic” membranes placed under the slab?

*If so, does any moisture travelling inwards along the slab dry out and not cause any concern for moisture travelling through the interior pressure treated bottom plates and into the bottom of the untreated studs sitting on them?

Thank you.

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  1. Expert Member
    Michael Maines | | #1

    Roger, if your concrete is placed on a good vapor-retarding membrane (it should be) and over a gas-permeable layer such as compacted crushed stone (it should be, if you're in a radon-risk zone) which doubles as a capillary break, then the only moisture that is going to reach your bottom plates is from the curing concrete, which is not enough to cause damage. If portions of your concrete, especially around the perimeter, are in direct contact with soil then some extra protection might be warranted, but in that case you will have other issues as well.

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