I think he has spot fixed and will know when they come off next week. As for the pva why shouldnt he have used it and what should he have done. Thanks
When using a cement based adhesive onto a gypsum background , you have to use an appropriate acrylic primer etc as this helps prevent a reaction between the adhesive and the gypsum backing
Using PVA simply seals the surface and :
A.. Does not prevent ettringnite formation
B.. It as mentioned above forms a skin which when wet , say by the adhesive bedding , becomes live and breaks the bond of the adhesive from the backing.
Spot fixing isn't correct application but not a deffo reason for tiles to debond , my money is on the PVA priming.