I have a two-story house. Recently, my 2nd floor shower stall developed a leak, as evidenced by water dripping from the first floor ceiling. The leak is small, a few drops of water after every use, and I believe I have now fixed the source of the leak (failing, cracked grout). I’m preparing to repair the ceiling and need some advice. The water dripped out around a nail head which developed a quarter-sized black stain and I assume this is mold. A few inches away, the paint has cracked and peeled away along a 2-foot long drywall seam. I was hoping to simply remove the loose paint, clean the black area with some bleach, re-spackle and re-paint the existing drywall. Will this work or do you think that I should remove/replace the affected drywall to eliminate the mold in the ceiling?
Mold needs three things to fester: air, food and water. While there is plenty of air and drywall is a terrific mold food, the fact that you have fixed the leak means that there should be no more moisture to feed a problem.
Secondly, the “black mold” that you think you have may not in fact be that at all. While mold is possible, water stains, caused by the reaction of water with paper, paint and rust, also can form a black spot. Regardless, a quarter sized area, even if it is mold is nothing to worry about, as long as the leak has been repaired.
My suggestion is to most certainly remove the loose paint as you suggested. Then, wash the area down with bleach and water solution just to make sure any mood spores have been neutralized. The next step is the most important, pain the area with an oil-based primer like KILZ. This will seal in the stained surface and prevent it from leaching through to the top layer after you paint. For the best results, prime the entire area and not just the spots that have been impacted by the leak.