Ok so firstly, do not use ready mixed!! These adhesives dry by dispersion and with the substrate being tanked odds are it will take ages to set, if It does set at all. Porcelain requires a polymer modified cement based adhesive I.e powder you mix yourself. If the tiles/grout colour are light then use white if they are dark you can use grey. Mapei adesilex p9 would be my recommendation as it is good adhesive, has a long pot life and is fairly cheap.
As above, PVA is a big no no for tiling, when it gets wet the water emulsifies it and it reactivates, creating an extremely poor mechanical bond between adhesive, tiles and substrate. I assumed the unibond was acrylic based. If it is PVA based then it will have to come off.
I used Wickes PVA. I was advised to prime the plasterboard in the tile shop. It does say on the instructions that its ideal for tiling porous surfaces before priming??
As I understand it, it is OK to use PVA as long as it is diluted. In which case the adhesive sinks into the surface. If it is applied undiluted then it will form a skin on the surface and easily peel. I have to admit that initially I forgot to dilute but quickly realised my mistake and reapplied a diluted solution 5/1 with water before the original coat dried. I am concerned at having originally applied an undiluted coat so how could I test?
If this is wrong I guess it will wash off? It is water based.
It's never ok to use PVA in a tiling application,
There's a very lengthy thread on here about this very subject.
Ditch the PVA & get a designated tile primer, either an SBR or an acrylic primer.
A good tile supplier will "Never" advise the use of PVA.
