primer and admixture

[rich172]

hi - just about to fit underfloor heating. guidelines recommend using a primer and admixture with a flexible tile adhesive.
is this just PVA or something more speciallised? (not sure if flexible tile adhesives are still cement based?)
cheers

 

[mikeyd]

I researched this when I put my underfloor heating down. I was told PVA has no place anywhere near any tiling. The admixture I used was bal admix and I used it with the cement based bal rapidset flexible.

I didn't have to prime the floor as I put down insulating boards which don't need it but I did prime the walls as it was newly skimmed plasterboard. Can't remember what I used but it wasn't PVA.

 

[Richard C]

Opinion varies but I would not recommend using PVA when tiling anywhere & certainly not in wet areas. Always follow the manufacturer’s instructions of whatever adhesive you’re using, used incorrectly a primer may affect tile adhesion. For example; BAL Redimix adhesive over new plaster only requires priming if it’s been over polished but the plaster should be primed if using a cement powdered adhesive; usually where large/heavy tiles are involved. Use a flexible cement powdered adhesive + Admix (not primer) when tiling over under floor heating & mix this with the adhesive.