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Dehumidifying long-term harms masonry? (self.homeimprovement)

submitted 2 years ago* (last edited 2 years ago) by diyrebel to c/[email protected]

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A top-floor room that’s not currently used has mold from excessive dampness. For a month I have been running a dehumidifier as it’s too cold to open the window.

Is this a good idea?

My concern: I heard about running a dehumidifier long-term in a damp basement is a bad idea because making the air more dry than the wall causes moisture to continuously flow from the outside in. That flow supposedly has the effect of washing the masonry through the capillaries and causing it to break down and weaken. In my case it’s not a basement, but similar because the exterior wall is non-stop wet from the frequent rains (possibly even leaky.. i think water seeps in).

I have the humidity set to 55%. I wonder if there is an optimum setting that would inhibit mold without overly causing water to flow through the wall (which is very old brick+mortar and rendered over on both sides, no insulation).

BTW, the water collected in the dehumidifier looks clean. Is it good for drinking?

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[–] [email protected] 4 points 2 years ago* (last edited 2 years ago)

It should be fine at 55 rh, do not drink that water, it is full of dust, spores, bacteria, and has leached the plastic, metals, and paints from the dehumidifier