I was in the process of remodeling the upstairs masterbath. The previous owner had OSB(?) over the 1/2 inch plywood and there seems to be some discoloration on the plywood due to exposure to water. There is no rotting that's visible to the naked eye. Should I be concerned about the discoloration or is it okay to leave it as is? Many thanks in advance.
I will be replacing the OSB with concrete backer board. Is it safe to assume that the discoloration on the subfloor is okay?