Whenever I have allergy problems, I start to clean. I have a problem with mold, so for the two weeks we’ve lived here, I’ve been suspecting the black mold on the bathroom ceiling as a factor in my breathing problems. This morning, a Saturday, I tackled the problem with Mr. Muscle, a cleaning product, a broom, a scrub brush, and the shower faucet which is on a flexible hose. I started in one end, and did a little at a time. I realized early that some of the plaster was coming down, but I saw that the under coat was whiter than that which was coming down. So, I kept on, and then I realized that the first section was coming down even more. So, now, we have a fan blowing in the bathroom and the window is open. Perhaps when it dries somewhat, we can sweep down the peeling pieces. How long until the undercoat is black again?