If he has been laying tile for any time, I can not believe it is a transfer problem. And I believe mapei Ultraflex can be used with porcelain. My mind initial goes to Deflection. Grout Lines should also be deteriorating. It does not smell like climate to me. They would normally not just pop loose. Popping loose failures normally with my stores means deflection. I have had recent climate issues on about 3 occasions and all of them crack the tile in sub floor joints.It sounds like either adhesion issues (Mortar) or Deflection (Vibration) I am curious as to what Bill V says. I do not believe it is a cut and dried answer without examination of home.

Thanks for your response. Our subfloor is 3/4" advantech plywood with 1/4" cementboard. I will have my husband check to see what we have for floor joists. Maybe it is possible our contractor didn't build a strong enough floor underneath.

In only one instance has a small amt of grout cracked, it has been intact on all of the others that have come loose. Our tile installer is really at a loss at why this is happening.

I'm not an expert but have done quite a bit of tiling. This sounds like the installer let the thinset get skinned over before setting the tile, or the tiles were dusty on the backside and the thinset stuck to the dust, not the tile.

I never back butter my floor tiles, but I periodically lift one back up and check for adhesion. So far, I have never had a tile where I could "pop" it off and have no adheasive on the back side.

If you subfloor is not solid you will have cracking grout or craking tile, but the tiles should still be bonded to the thinset. There are some subfloor material that thinset won't stick well to and tiles can come loose, but then the thinset is on the tile and not sticking to the floor.

I agree with MacyBaby. If your installer spread more thinset than he could lay tile on before it began to dry (skin) on the surface, it might not adhere to the tile as well as it should have. I would be even more suspicious this was the problem if several tiles next to each other are coming up but other areas seem to be very well adhered. I'm using the same thinset on some ceramic tile I'm laying now. Time will tell if I have problems but I am buttering both the floor and the tile...this takes forever!

It is Mapai ultraflex 1. So far all of the tiles that have come loose are in the foyer. We did 3 other rooms at the same time and so far they are ok.

"Our subfloor is 3/4" advantech plywood with 1/4" cementboard."

"20x20" porcelain tile"

That is very likely not a stiff enough floor for tiles that large.
The cement board adds no deflection strength.

If the joist spacing is 24 inches the floor is definitely not stiff enough, and even with 16 inch OC joists is probably allowing to much movement unless the joists are oversize for the span.

Large tile on a regular 1/360 floor are not going to stay in place very well.
Large tiles are well into the 1/720 deflection requirement.

We have 24"x24" porcelain floor tiles that look like marble and have a very slight grout line (maybe 1/16"). Our contractor had to raise the floor up so high to make the tile level with the hardwood floors but didn't anticipate it until it was too late. So, rather than floating the whole floor up and using just a little thin set, he used all thin set. Went through a LOT of bags at his expense. Now, several tiles have a hollow sound when you walk on them where the thin set settled and there's air between the tile and the floor. I'm wondering if there's a recommended method for repairing the hollowness? The grout lines are so tight, that I'm afraid trying to remove them would crack them. And we too, only have a few tiles left for emergency breaks. Can anyone help with a suggestion for repair? Would drilling a hole in the tile and squeezing thin set down into the hole help? HAHA! I'm clueless. Thanks in advance.

Omg,i know this is from 2010 but for anyone looking for solutions on a same problem, its not the morter ,its not the floors its not deflection either that only happens years after tile has been installed, one simple trick the durock or concrete (never ever bare subfloor or over old tile thats is absolutely lazy dirty work) where you are installing must me wet,the tile must be wet everything must be wet,when concrete and durock soak up the water its creates suction. Same if tile is wet that does the trick,thats how it works in tuck pointing as well laying cinder block for commercial walls ,fyi never morter durock ever ever

never had this problem but i fixed many do it yourself projects and so called jack of all trades or handymans poor quality work,even when licensed that doesnt mean they know what they are doing,look for experience and verifiable references ,

cant beleive no one knows this,this separates professionals from handyman being informed before messing with someones property

thats all keep everything wet with a spray bottle

I rent my house and the ceramic tile has fine thin cracks in it, mostly kitchen area...this was like this when we moved in. seems like the grout breaks away, and the tiles clicking and sound loose when we walk on it. Someone suggested this might be, that the house is not level?