to prime or not to prime!!!

[grumpygrouter]

plaster board and ceramic and ceramic adhesive is okay not to prime.
plaster board and porcelain/marble etc, you use cement based adhesive (has to be mixed) the yes bond neat with pva, or at least 1:2parts water.

Have to disagree there Rab, PVA is genreally deemed not sutiable by the vast majority of adhesive manufacturers as a primer. Acrylic primers are what is recommended now. Granfix is the exception as they specify PVA for one of their adhesives.