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Water in first floor ceiling

We have veneer plaster ceilings through out our home. The 2nd floor bathroom sink ran over for about 10 minutes. The water ran into the first floor ceiling which is 2 x 6 construction. From there it ran along the blue board, which is the backside of the first floor ceiling. The water drained to the first floor along the seams of 6" x 6" barn beams in the ceiling. We were able to dry out the floors, which are tongue and groove oak, but are concerned about the water that may still be laying in the first floor ceiling on top of the blue board. I did put several small nail hoes in the diamond coat through the board, but there does not seem to be any water coming out.
Question: Should we replace the ceiling and do you think mold will form in the area between 1st floor ceiling and second floor flooring?

Re: Water in first floor ceiling

First, does your bathroom sink have an overflow hole? This safety feature prevents water from overflowing down to the floor.

Regarding the ceiling: depending on the extent of the damage, you may need to replace some, or none at all. And as far as mold, it can grow, if there is a sizable amount of moisture trapped along the framing, with no chance to dry. The enclosed area must be aired and dry. If you could use a small fan, it can help a lot.


Yes, we do have overflow drain, but that was plugged by sink contents. Other than tearing out portion of ceiling there is really no way to get to the moist area. We have a dehumidifier going on both second and first floor. The downstairs one took out 20 -24 pints in about six hours. Seems like a lot. Obviously we had dried the floors with towels the night before. I guess we could buy one of those inspection cameras and drill a small hole or maybe a moisture detector.

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