Thinset coverage?

[DIYMudder]

Observed this coverage issue on job I hired out, after pulling two tiles off. 1/2 inch trowel used. Concerned about air spacing, was told air help Ditra Set dry, and was OK because slight Kerdi imprint was seen on thin-set. As homeowner, I always went for more uniform compression. Any I being too picky? Thanks.

[Lou_MA]

No, you’re not being too picky.

A thin coat of thinset should have been burned onto the Kerdi, as well as the back of the tile. And you shouldn’t be seeing those notches...they should all be compressed into “peaks” of thinset (kind of like lemon meringue), aiming for 100% coverage.

[makethatkerdistick]

What concerns me about this installation is whether the Kerdi has been properly attached to the wall as well. If not, this might spell disaster. Do you feel a lot of blistery / bubbly hollow areas when you let your hand glide across the Kerdi?

They didn't use enough thinset to really float the large-format tile on the wall (as you can see from the ridges that are not collapsed). Enough is required to manipulate the tile to even out lippage. No burn-in as Lou observed. Not to even mention poor coverage. This should be close to 100% in a wet application. You don't want water to gather behind the tiles.

Funny that they used the leveling system.

The longer you wait to remove this, the more likely that the Kerdi fleece will be pulled off in the bonded spots when removing this tile.

[rmckee84]

Nope, nowhere close to the coverage or bond needed. Looks like thinset was troweled on the tile and nothing was burned into the kerdi. Like mentioned the ridges should be collapsed, installer has no idea what they're talking about giving an excuse about air and curing....

[jadnashua]

Industry standards call for 100% of the edges, and at least 90% coverage over the entire rest of the tile on a wet surface (like in a shower).

FIrst, you need to burn thinset onto the wall, then add more and notch it...then, burn a coat on the back of those larger format tile, then set the tile. On a larger tile like that, the only way you'll collapse the ridges of the notches is to move it back and forth across the notches. Those voids behind the tile can lead to moisture buildup, and the lack of full coverage will also make the bond MUCH weaker. While you might not notice on a porcelain tile, if it were say a natural stone or a glazed ceramic, those voids would likely end up making the tile show striping after awhile from the variations in moisture that got behind. Neither the tile nor the grout is waterproofing, and some moisture will get behind the tile in a well- used shower.