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In my interior wall a couple of weeks ago we noticed the paint bubbling with moisture underneath. The pattern made me think of efflorescence, and there is a fine crystalline powder in some parts.

My understanding is that the wall is a brick veneer, an interior layer of bricks, followed by lathe and then plaster and paint.

There is also evidence of previous repairs to the mortar of the brick outside.

There's obviously moisture, but I am unsure where from. If it is efflorescence, I don't get how that could go through that many layers without also showing down in the unfinished basement below.

After wiping the powder, it reappeared over the course of a week (almost no rain that week). Left over moisture?

Other candidates for moisture are a window right above this spot (have now recaulked some gaps) and an adjacent chimney that has a good looking crown but no rain cover on the actual opening (used for furnace).

Any thoughts? Is this efflorescence? If so, how could it go through all those layers without dripping down into basement?

interior wall

outside wall opposite damaged interior

efflorescence?

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