I spent the day demolishing a bathroom. The previous occupant/owner had put down an additional layer to “repair” some water damage, noted by an approximate one inch step up upon entering. Everything seemed reasonably solid, but since I’m replacing everything (including the tub) and changing some walls around in order to relocate the washer and dryer there, I decided to pull up what was there and do the repair right. I am so very glad that I did. The additional layer? Old highway construction signs – you know, back when they made them out of wood instead of metal. Underneath of that, there was significant damage to the subfloor, and even some minor damage to a couple floor joists. Repairs are ongoing.
EDIT: Garand Gal
called my integrity into question requested pictures in the comments, so here is one. The sign/floor repair material has already been removed from the bathroom, and is propped up against the wall. Observe: