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Question DetailsAsked on 10/12/2015

why is there white powdery stuff growing on inside masonry around my chimney?

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3 Answers


Sounds like either mildew or feather mold (very feathery like cobwebs usually) or lime bloom (more of a powdery buildup) - in either case, caused by moisture passing through the brick and either staying moist enough it supports mildew/mold growth, or wicking through and depositing lime from the mortar on the surface. Sounds like you have a chimney leak - leaking crown or leaking / missing cap maybe.

Chimney Sweep would be your Search the List category for inspection and repair - and if has not been cleaned in awhile, should probably do that as well - may well be required anyway so he can see what is going on inside the chimney.

Answered 5 years ago by LCD


This is called efflorescence, a mix of inorganic salts caused by water getting into the masonry. If you have a concrete slab foundation, this water could be coming from the slab. The water enters the wall from the exterior and evaporates to the interior, depositing the salts. They wash off with water, but they will continue until the water problems is solved.

Answered 5 years ago by iamgerardj


BTW - if effloresence, that is material that is being leached out of the mortar, so the mortar is losing the strength the longer it goes on - a little is not critical, but years worth can be. Vinegar will remove it, but go careful not to get it on the mortar joints because vinegar will dissolve it - use a wetted but wrung out firm sponge so you are running over the surface rather than into the mortar joints, and work diagonally to the bricks except for the last pass to avoid working down into the mortar joints. And sponge off with wet (but not dripping) sponge for several passes to remove residual veingar, because many bricks have enough limestone or similar materials in the clay to be damaged by prolonged exposure too.

Bear in mind, if your bricks have soot on them (from fireplace or artistic) this process will stain or blotch it - no avoiding that, though to just remove the bloom you can use a still bristle brush like a horse brush or toothbrush to just dry scrub it off. Do NOT get on hearth or rug where it can get ground in and leave a white mark.

Answered 4 years ago by LCD

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