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I am doing some repair work in an old church. Mostly I am scraping old rough cracked plaster and install sheet rock over it. There are how ever a couple of places throughout the church where the plaster has a white powdery chalk growing out of it. according to the church they have been sanded and painted in the past, but reaccure.
What causes this and what are some solutions to fix it right?
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Efflorescence, perhaps? Caused by water moving through the plaster, dissolving it, and then depositing it on the surface. It keeps coming back because the leak behind the plaster wasn't fixed. You'll probably want to tear into the wall at those points to locate the leak site and correct it before putting in new material that'll also be ruined.
*yes I agree with Barry, it is efflorecence most likely. To my knowledge it is salts in the plaster, render, bricks or mortar being leached out. Very difficult to remove. Seem to remember Barium Carbonate being used in its' cure but can't recall if that was to be used in the intiall mortar mix or for clean up after.
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I am doing some repair work in an old church. Mostly I am scraping old rough cracked plaster and install sheet rock over it. There are how ever a couple of places throughout the church where the plaster has a white powdery chalk growing out of it. according to the church they have been sanded and painted in the past, but reaccure.
What causes this and what are some solutions to fix it right?