Flooring Tile - Hollow Tile

I layed ceramic tiles on an existing slab and am having problems in only one room. About 9 of the tiles in various places are hollow sounding and the grout is not only cracking, but flaking out in large chunks.

I read several posts about the same problem and removed the hollow tiles. I removed them by scratching out the grout and then I put a putty knife under the tile and wedged it out intact. I found that the glue underneath was still wet, even after letting it set a day before grouting and several weeks after the install.

I installed new tiles and this time I made sure that the tiles were seated by standing on them. After waiting two days this time, I applied the grout and thought all was well.

It has started again. The only thing I can think of is that on various spots of the slab, the concrete is real smooth, almost glass like.

Should I remove the tiles again and etch the concrete? I'm concerned about fumes and damage to the neighboring tiles and grout.

I don't think it's a bad batch of glue because a few hours after pulling up the the first batch of hollow tiles, the glue set. The glue also seems to be holding in the other areas, just a few spots.

Any help would be appreciated because I need to move onto other projects.

What kind of setting material are you using? Is it a premixed adhesive in a bucket or a thinset mortar in a bag that is mixed with water? I'm betting its premixed in a bucket, right?

I'm waiting for the answer too! :coffee: I think I know the answer but need confirmation. :D

Jaz

http://www.citizenarcane.com/files/2005/April/12/elmers_glue.jpg

Ok..you guys are just making fun now. I did the same thing before I knew better. Well, someone elses problem now.

mcslat...hope you come back and let us know whats up. Don't take offence, everyone gets bad advice.