Andy Hall wrote:
On 2007-01-04 14:55:48 +0000, Stuart Noble
said:

Andy Hall wrote:
On 2007-01-03 14:40:50 +0000, Grunff said:

The Natural Philosopher wrote:
Grunff wrote:
PVA them first.


Don;t bother. Waster of time. Makes the adhesive take longer to set
as well.

Well, although I can't say I've tried with and without, my reason
for always PVAing is to provide a dust-free surface. Both ply and PB
tend to be quite dusty, especially if you've been plastering/filling
in the room. A coat of PVA provides a sound, dust-free surface to
tile onto.

I was curious about this one, so I contacted the technical
departments of three leading adhesives companies - BAL, Dunlop and
Ardex.

I can't believe you take any notice of what manufacturers say. It
either works or it doesn't and, in this case, you can tell when you
slap the first tile on. If it needs sealing, then seal it. I think
perhaps you're looking for certainties in situations where the
conditions of use are unknown.

Well.... generally I find that following the manufacturer's
recommendations on the use of a product is a Good Thing. It avoids
embarassments like the Legendary Hacksaw Incident.

In the partcular case in point, I don't agree with you that one would
find out after the first tile. It's entirely possible that it would
appear to stick OK at first and then at some point down the road,
adhesion would turn out to be
poor and the tiles would begin to fall off. That would be something
of a waste of time an materials since one would then need to remove all
of the tiles, carefully clean them off, rectify the problem and stick
them back.

If the problem was that the substrate had not been sealed and should
have been then it is not quite so bad, but if one had sealed it and
shouldn't have done, then the thought of replacing the substrate as well
is not appealing at all.

In comparison, a few phone calls is hardly a large investment.

Many years ago, for the purposes of going to customers in remote places,
attending trade shows as an exhibitor or whatever, someone taught me the
principle of the 6Ps. In layman's terms this is Proper Preparation
Prevents **** Poor Performance.

This would appear to be a classic opportunity to apply that principle.

One manufacturer indicated that the substrate should be dusted and then
wiped with a damp cloth and allowed to dry because their adhesive works
better if its liquid content can soak into the surface - PVA reduced
that, they said.

Another said that PVA was better because it sealed the surface, cut down
the dust and prevented the liquid content of the adhesive soaking away
quickly into the substrate.

Perhaps the products are different. Probably I'll use a very weak PVA
solution and achieve the apparent benefits without the risks?



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.