Are they porcelain tiles ?
Ceramic tiles absorb water from the adhesive so the adhesive dries out.
Porcelain and stone tiles will not absorb water easily.
A normal wall will also absorb water from the adhesive but some finishes will prevent this (like tiling over glazed ceramic tiles).
It may be your wall will not absorb water because the pva you have put on it has sealed it.
Ceramic tiles absorb water from the adhesive so the adhesive dries out.
Porcelain and stone tiles will not absorb water easily.
A normal wall will also absorb water from the adhesive but some finishes will prevent this (like tiling over glazed ceramic tiles).
It may be your wall will not absorb water because the pva you have put on it has sealed it.
