Thinset

We've got a big concrete porch tiled with 17-inch tiles. It's under roof, but because of the aluminum framing for the screen enclosure, which sits on the floor and dams up any rainwater, puddles have accummulated from time to time.

We never thought much about it, since we're in South Florida and water evaporates. 2009 was a wet, wet summer. We were gone most of the summer, and when we got back, about 30 tiles had been loosened. In one case, tiles were actually buckled -- adjacent tiles actually heaved up against each other (what causes that?).

Now I am chipping the thinset, or what remains of it, off the floor. Some of it is solid scab. Much is dust, or has separated in big sections from both the tile backs and the concrete floor. Soaking seems to be removing the thinset from the tiles we;ve removed. They must be saved or we will have to have the whole porch retiled because they don't make this tile any more. I am almost sure this is thinset, not mastic, and I am wondering what we can do to keep this from happening again.

It's called tenting, it's caused by grouting the perimeter of the install not leaving any room for expansion and if direct sunlight is hitting this floor, that makes it worse.

Could be other issues too, like if it's truly Mastic and not thinset, wrong thinset used, coverage, etc.

Thanks for your help. This installation was done about 10 years ago, and we are informed that thinset is sturdier now, guaranteed to hold up for 15 years.

As for the grout lines, I notice that the thinset under the tiles is pretty much continuous over the floor surface. I'm assuming you mean that when we reinstall the tiles we should leave some space on the concrete floor around each tile free of thinset so the grout, when it expands from water or heat, will not cause loosening. My husband is convinced that regular sealing of the grout (as was done originally with a silicone sealant) will prevent another episode of tile loosening. I am not so sure.

'm assuming you mean that when we reinstall the tiles we should leave some space on the concrete floor around each tile free of thinset so the grout, when it expands from water or heat, will not cause loosening.

No, The perimeter of the installation needs to be free of thinset and grout. When you reinstall the tile, you do want to clean out any thinset purging between the tiles, though. It's easier then than when it's hardened.

and we are informed that thinset is sturdier now, guaranteed to hold up for 15 years.

If the right materials are chosen and installed properly, it will never have a problem. Your first installation was grouted tight to the walls. Every time it heated up, the floor and walls would expand and place a tremendous amount of force across the field of tile. Eventually, the thinset bond which weakens over time from these shearing forces cannot withstand the pressure build up any longer and the tile releases from the slab. It peaks in the middle because that is where the forces from all direction meet one another and have nowhere to go but up.

Exterior installations or interior areas subjected to lots of direct sunlight need not only perimeter expansion joints, but they also need expansion joints every 8-12 feet within the tile field. Around the installation they can be left empty and covered with molding or filled with a color/texture matched caulk. Within the field, you can use a color/texture matched caulk. Silicone would hold up best and both Laticrete and Tec make many of the grouts in their color pallets in a 100% silicone caulk.

Follow those steps and the install will be forever.

My husband is convinced that regular sealing of the grout will prevent another episode of tile loosening.

Ya know, the tooth fairy visited my daughter last week I'll leave it at that

I am not so sure.

I too married a very smart lady.