Many years ago, I placed vinyl sheet flooring over the tile floor of our bathroom without using adhesive. I simply caulked all the way around the edge. Over time, water got under it and I noticed mildew in one of the corners that was lifting up. When I attempted to remove the vinyl flooring, the backing apparently is now stuck to the tile and hardened along with the mildew. It is extremely difficult and tedious to try to scrape it off the tiles. Is there a solvent I can use to make the job easier?
I'm picturing a felt or paper backing that has been partially dissolved and then dried out. It's probably not much different from what happens when you accidentally lay a magazine in a bit of water on your countertop at breakfast and return after work to find it glued down solid. The binders in the paper dissolve and create a weak glue.
You haven't mentioned what you've tried, but I'd start with a simple dishsoap solution. Water caused the adhesion, and water may remove it as well. A bit of soap won't hurt.
Otherwise, I'd look at something fairly mild like wallpaper paste remover first. Harsher products are likely to damage wall finishes and grout. You could also create your own solution of white vinegar and/or lemon juice. More on that.
You can try Xylene or other volatiles. Because I'm a tile layer by trade my answer to everything is muratic acid. 50/50 w/water. If that doesn't work find s Ace hardware (only place to get this) buy a big hug of 'Wink' brand rust stain remover. Its mainly hydrofluoric acid. It will breakdown any adhesive - The Texas Tile Guy
You can try Acetone or nail polish remover, but you need some really good ventilation. You best bets are actually a heat gun, hair dryer or clothing iron. Those will heat up everything & since it wasn't glued it should just peel right off with that assistance.
Heat gun & hair dryer is usually 10-15 seconds at your starting point & then goes a little faster as you keep expanding the heated area. The clothing iron needs the surface sprayed with water & use it in steam mode to then just move it around in small circles.
You'd be just trying to heat things up & not burn nor melt anything. Test the heat with your putty knife to gauge how long is needed frequently & you'll soon get into a rhythm.