I just tore down wallpaper in a wooden house from the 1930s and revealed the masonite which has many small black dots, but only on the masonite panels that are against the exterior walls. Unfortunately, they are so small that they don't even show up in the camera, otherwise, I would have included a picture. Does anyone know a way to determine if it's mold, or is it a false alarm, or what should be done in that case?
