The grout was coming up from around the drain on my shower floor. When I removed the grout the tile was loose. Under the tile is sand, no mortar. The house is a concrete slap. Some of the sand had mold in it. I removed the moldy sand. It seems the tile is laid on a bed of sand about 3/4 of an inch thick. How do I replace the tiles I removed

Is there any mortar stuck to the back of the tile?

Sounds like it might have been wet-set, where the tile is set in the wet mud floor with a dash of thinset.

I'd be more worried about the mold growing on the floor. The liner might be lying flat on the floor, which is not good. I wouldn't put the tile back under those conditions.

I second that, now would be a good time to re-do the shower floor. What's happened is the mortar is crumbling after years of being saturated with water. My advice would be to get a pro to replace it for you with a Schluter drain and pan. This means that the bottom 4 to 6 inches along the walls will have to come out as well.

The problem is I can't afford to hire a pro and redo the floor and I am an old guy, be lucky if I am around another 10 years. I have removed a large part of the tile and have read about the sand mix+sand. If I remove the old dry pack and add new do I just lay the tile on the new. Will the tile stick to it?

You can use Quikrete sand topping mix and add a little sand to it, I use that sometimes. After you have it packed and pitched properly, after it dries over night you can install tile over it.

The key is going to be verifying that the liner, or whatever waterproof layer is under the deck mud, is still intact with no holes. You'll have to be very careful not to damage it when you take out the existing deck mud.

So that you don't do all this upcoming re-install for nothing, once your demolition is finished you may want to do a flood test and check for leaks.

We're here to help with any questions you may have, and there are plenty of how-to pics on the site.

Thanks a lot. I really appreciate the help