On 4 Aug, 21:51, The Natural Philosopher wrote:

I bet you have a waterproofed wall or summat.

blockwork, dot-n-dab, 12.5mm standard plasterboard, skimmed, left a
couple of weeks, sealed with Ultra Tile Prime IT FP (NOT PVA!), then
tiled a few days afterwards (primer dries in an hour)

Leave the batten up for a couple of weeks. It takes a LOT of time to dry
through the cracks.

That might be a solution, but I can't imagine most people leave
battens up for a couple of weeks. Typical advice seems to be to grout
after a day or two!

FWIW I've just tried to pull off the first tile, applied Thursday
(i.e. 6 days ago), and managed to get it off just by pulling firmly at
the exposed edge with my fingers. Adhesive behind this one is slightly
damp (or dry-ish!) and crumbly, not solid at all.

I have personally found that Evostik waterproof DOES set faster than
simple air dying cements.

I have Ultra Tile ProFlex SP +ES for the rest of it (i.e. the
porcelain tiles + floor tiles) - I might just try it with these
ceramics. As it's stuff you mix up, I don't suppose it needs air to
dry.

Cheers,
David.