On 2007-01-05 13:16:39 +0000, The Natural Philosopher said:

I think they definitely are.

Ive tiled 4 bathrooms and 2 kitchens and about 60 meters of slate floor
in this house. More in previous ones.

The typical crap wall tile adhesives that also grout, seem to be a sort
of polyfilla. They grab fast on unsealed walls, but are pretty weak,
and water does seem to soak into the grout, and I am not sure it sets
anyway. Just dries.

For wall tile use I now use evostik waterproof. This seems to also be a
drying rather than curing glue, but its flexible, fairly fast grabbing
and seems highly water resistant. Its sort of feels like no more nails
actually. Then BAL grout with a little PVA in critical areas IS a
setting type product. and is my choice for grout. When I have used the
evostik over non porous surfaces its taken an age to dry and set -
several days.

Finally I use ARDEX floor tile cement - Ive used two - a rapid set
straight and a flexible slow set. I had trouble with dust and a little
trouble where I didn't seal the screed properly..it sucked the wet out
and the setting was weak. Ripped up the offending slate and replaced it.

So the PVA before tiling is all about dust and/or not sucking up water
out of compounds that don't DRY, but SET. In my case Ardex only.

It does **** all to waterproof anything except a mortar mix. Tiles are
1000 times more waterproof, its only in the grout where it has any
possible uses in that area.

Thanks for that.

I certainly felt after reading the information and talking to the
technical department of Ardex that the quality of info provided was the
best of the three. I'll probably select their products for that
reason alone.