Andy Hall wrote:

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.

A tile should be difficult to pull right off a after a few minutes.
Slides a little but will hang on to even an overhead surface quite
happily without support. I've never known that sort of bond to get worse
as it dries but, if you don't have it to start with, you might consider
sealing the plaster (or using more adhesive).

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.

Fine if anyone knows what they're talking about, but these technical
staff are not ex-tilers or chemists. They're just reading from a script
and telling you their name's Darren and to have a nice day.


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.

Indeed. Prepare your surface accordingly, but someone at the other end
of the phone has no idea what *you* mean by "dusty" or "porous".

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.

But all these adhesives contain pva, or very similar resins, and the net
result is likely to be the same

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.

Different call centre I expect

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

Unlikely to do any harm I suppose.