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Community and Q&A

Moisture control for brick-on-block

Jeremy_G | Posted in Energy Efficiency and Durability on

I’m working on a plan to improve the energy efficiency and comfort of my 1935 Dutch Colonial in the D.C. area. And I just discovered that I have 8″ brick-on-block walls, except the front and back walls on 2nd floor, which are presumably framed. (The gambrel roof acts as the front wall, which has 3 dormers, and the back wall is nearly all one dormer.) Lath and plaster are on furring strips. The exterior brick is painted.

One of the things I’ve learned to think about since reading GBA is moisture management. Should I be concerned about sealing up the gaps between the plaster and masonry? I’ve started foaming and caulking the gaps between the joists and basement wall, and have tucked some backer rod in the gap between the floor and baseboards after removing the shoe molding.

There are, of course, many gaps to seal up — and I’m sure I can’t access them all. The windows were replaced about 5 years ago and it looks like they have been caulked properly both inside and out. I don’t yet have a good idea of how the framing interfaces with the masonry between 1st and 2nd floor.

So, I want to get things sealed up within reason, but don’t want to cause a moisture issue, especially when we have big changes in temp and humidity.


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  1. GBA Editor
    Martin Holladay | | #1

    I think your interior caulking and sealing efforts are all beneficial.

    Be careful with exterior caulking, however. Some homeowners accidentally seal weep holes near window sills, or weep holes at the base of a brick wall -- and you definitely don't want to do that.

  2. Jeremy_G | | #2

    Thanks for the response. I haven't seen any weep holes, though haven't specifically gone looking for them, either. I'm guessing the brick and block are mortared together as a unit, so perhaps there are none? There appears to be a black paint on the inside of the block that I assume is for waterproofing. (Early photos of the house show natural brick -- it was painted later.)

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