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Cause of blisters in plaster

pjpfeiff | Posted in General Questions on

Attached are pictures of plaster damage near stained glass windows in a church–what are the likely causes?  Other people (with no special expertise) had decided the windows were leaking, but the windows appear well-sealed and I see no other evidence of leaks.  I’m not familiar with the building construction, but my guess is brick facade with a wooden frame. 

My current hypothesis is that the brick in those areas is getting overly wet, but there is no obvious reason why and no staining on the outside.  In any case, does a humid wall cavity cause this blistering?  Is it possible that the plaster keys are in contact with the brick where there is damage? There is another spot of blistering (unpictured) that is below grade and near a clogged gutter, so I assume those things are connected.

Climate zone 4, central Virginia

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  1. Expert Member
    BILL WICHERS | | #1

    That looks like pretty severe water damage to me. My first thought when I see something like this is "there is a problem with the flashing somewhere". I'd check head flashing on the windows, and anything up higher on the exterior wall in the general area of that problem. I'd be especially suspicious of anything with a corner on the exterior in the general area of that problem. Chances are water is sheeting down the wall, getting behind some trim somewhere, then making it's way into the structure.

    You'll want to check this out, since if it's bad enough, it can cause deterioration of the structure of the wall.


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