tiles comming up

We supplied a customer with 80x80 porcelain tiles which are comming up. The sub floor was screeded and has underfloor heat. Bal adhesive was used and they did a site visit to check the problem they said the wrong specifcate had been used. The adhesive has stuck to the sub floor but no adhesive is sticking to the tile. Is this a problem with the tiles as the customer is saying they are faulty.

Bal adhesive was used and they did a site visit to check the problem they said the wrong specifcate had been used.

That right there could be the biggest problem. I'll assume the screed was at least 2cm thick above the heat, reinforced and it's in perfect shape without cracks, etc, or you would have mentioned that.

If the tiles were set with an unmodifed thinset, which is pretty much just sand, portland cement, and a few little additives to make it hold moisture a bit longer for proper curing, it will stick just fine to the mud bed.

The installer obviously did not back butter or use a burn coat (scrape a layer over the back of the tile) or it wouldn't be clean when it came up.

There could have been a release agent on the backs of the tile from the kiln. That would have created a layer of nothing between the tile and the thinset below. The tiles around the perimeter that may have been cut with a wet saw and dried off which would have washed away the release agent, are they sticking?

Was the heat turned on prior to the floor reaching it's full cure?

Proper expansion gaps around the room (s)?

I could go on and on listing issues that could cause problems but no, the tile itself is not defective. Defective tiles would be those that crown or cup out of specified tolerance, tiles with imperfections in the glaze, stuff like that. Tiles coming off a floor without thinset on the back, no, that's not a defective tile.

I don't mind tellin' ya I'm lost!

What the heck is "Bal" adhesive?
The "subfloor was screeded", with what? How?
The wrong "specifcate was used". What is "specifcate"?

My vote is one of two things at this point:
1. Kiln release on the tile - installer error.
2. Premature launch of the heat system.