Can you tile on wet plaster?
Keeping this in consideration, can you tile directly onto plaster?
Tiling onto plaster is relatively straightforward. When you place tiles directly onto plasterboard, this often means you don't have to prepare or prime the plasterboard prior to doing it. If the backing is strong enough to support the weight of tiles, tiling can be performed on numerous clean, even and dry surfaces.
Correspondingly, can you tile over plaster walls in a shower?
Fresh plaster, whether applied as a patch or to the entire wall, must dry completely before tile is applied. The adhesive and tile will block moisture from evaporating. Tiling over damp plaster causes the wall to fail because the plaster won't become strong if it can't dry out.
Short answer. No, never use PVA to prime a surface before applying tiles. The acetic acid produced when cement and PVA come into contact would render the adhesive and grout useless.