Flooring Tile - flexbond not bonding

we have a very large problem of 20" X 20" floor tiles lifting from the reccomended "flexbond" mortar. We screwed down wonderboard over our existing plywood foor, used the reccomeded sized tool (large grooved) and laid an entire downstairs (5 rooms) of tile, and they are lifting, not one has a crack, but numerous throughout the project are loose on top of the set mortar! what could we have done wrong? could this be a flexbond product problem?

Few things:

1. Were you backbutter everytile to ensure 100% thisnet covereage?

2. You worked beyond the life of the thinset, meaning the thinset skinned over.

I highly doubt it's a flexbond issue.

Did you press the tiles down into the thinset? They just don't sit on top of it.

tl

You need to provide a lot more info than you did. For starters, what kinda tile, ceramic, porcelain, natural stone? Large format tile like this need a very stiff floor and if its stone, even more so. Whats the size of your floor joists, whats their oc spacing, and their unsupported span from below? How thick is the plywood subfloor, and how many layers? Was the plywood square edge or t&g?

Exactly what size trowel did you use to set the tile? Did you pull a few tiles to make sure you were getting adequate coverage? Did you mix the thinset to the proper consistancy, let it slake for the proper amount of time, then remix? Did you make sure not to exceed the open time recommended for the product. Did you set the tiles immediately after you combed the thinset, or did you allow it to skin over? Did you backbutter the individual tiles?


We screwed down wonderboard over our existing plywood foor,

Did you bed the wonderboard in a fresh bed of thinset as per Custom Building Products instructions?