Help?! I am regrouting the shower and found caulk under grout, tiles falling off

[Pikapupp]

I am new here. A couple of weeks ago, the soap dish fell off the wall. So I bought a new one. I had been noticing that grout had been occasionally flaking off. So, since I had to grout the new soap dish anyway, I decided to regrout the whole thing. When I started removing the grout, I discovered that there is caulk underneath. So I started scraping it out with a box cutter. Then tiles started falling off. I think this installation was done when the house was built in the 60s. They used some brown substance to adhere the tiles to the wall. I have done a couple of tiling projects before. About 20 tiles have come off. At this point I am not sure what to do. I haven't been able to remove much of the brown substance from either the wall or the back of the tiles. I am afraid that if I use thinset to put the tiles back, it would be raised and the grout lines are very tight. Am I going to be able to repair it or am I now stuck with ripping it all out and starting over? I've tried to attach photos.

[jadnashua]

It looks like mastic (a glue) and I cannot tell what the substrate that it is mounted on. Take something like an awl and poke at the board behind - if it is soft, it may just be drywall, and the only hope is to tear out the surround and start over - possibly after fixing any rotting studs that may be there. This is a good example of why you should not use mastic in a tub/shower surround - in fact, there are very few places where mastic is the better thing to use! It looks like the mastic had started to skin over before they placed some of the tiles - done well, it would have good coverage on the whole tile.

[cacher_chick]

I don't know what that stuff is, but I've seen a lot of bathrooms from the 60's that used it. Once something starts falling apart like that, the rest is sure to follow.

You could cover the whole works with a solid surface surround, or tear what you have out and start over.

[Pikapupp]

I think the substrate is some sort of cement. It is hard. I took the ring off around the shower handle and poked at it there, it seems to be about an inch thick and hard like cement. I'm not sure what the black stuff is. What are my options?

[jadnashua]

It could be a mudded wall, but if they went to the trouble to mud it, it would be unusual to then use mastic on it. You may be able to scrape or scarcify the crud that's on there, then I'd use thinset to either reinstall the tile, but if that may fell off, I think I'd rather remove them all and start over. Your call. There are a few oscillating tools with diamond cutting edges that might make quick work of it, but unless you get a cheap one from say Harbor Freight, a decent one costs a lot of money for what may be a one time use.