his will explain why p.v.a has no purpose in tiling-http://www.tilersforums.co.uk/tile-adhesive-grout-prep-forum/2511-p-v-versus-primers.html?highlight=p.v.a
i would use a rapid setting adhesive,it doesn't have to be flexible,and i would also seal after laying and after grouting,nake sure you wipe away any excess adhesive that comes through the tiles when laying