sm_jamieson wrote:
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.

Non-cement-based, cures by drying out.

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.

Cement-based, water needed as part of the cure, so stop it soaking in.

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

The BAL adhesive I used specified BAL primer (it would !). I may just
have used PVA, but I had spare primer from the the BAL WP1
waterproofing so used it anyway. I didn't smell like PVA (had an
ammonia smell) - the BAL stuff is all polyester-based I believe.
Cheers,
Simon.

You bear out my experience exactly.