I decided to take on the project of a DIY 1/2 bath renovation. We have burgundy wall tile in the bathroom that I had hoped would be easy to remove. The tile is original to the house built in 60s. The tile itself came off fairly easy but now I’m left with this hard cement-like adhesive that won't budge. I've tried sanding but it makes a big mess with little progress. A tried a goo gone type of solvent that did nothing. I need help and ideas. It's a hard adhesive not sticky or soft like a glue or putty.
A bit late now, but adhesives/tile mastics from the 1960's often imply "check for asbestos before making dust out of them." It's not the "classic black mastic" but still...
Remove the drywall, adhesives and all, take care of anything needing fixed or updated while the wall cavities are open (insulation, electrical upgrades, etc.) and put on new drywall (or cement-board if re-tiling.)
Fighting with old dried mastic is a waste of effort .vs. rip and replace with new, plus you get to fix anything in the walls that needs fixing. But even if nothing in the walls needs fixing, replacing the drywall is far less effort than trying to scrape that junk off without destroying the wall, and gives a better surface for whatever you will be finishing with.
Below are a bunch of options. Choose based on your budget or if you value your time then skip to option #4.
You can try a coarser grit when sanding like 36. Particularly useful would be a random orbital sander. A belt sander would be far too uneven. Wear a respirator.
Get an SDS chisel and the proper tool.
Get an oscillating tool and hard scraper blade.
You need to either find a good drywall finisher that can skim coat the entire wall or rip out and replace that sheetrock.