On 2008-02-07 13:21:53 +0000, DavidM said:

I'm about to put ceramic tiles onto the splashback behind the kitchen
worktops, up to the underside of the cupboards. Currently there is
18mm standard (ie not external grade) ply boarding securely fixed to
battens on the wall, and I'm planning on tiling straight onto the ply.

All the "tiling onto ply" advice I've found on google is about floors.
Flexing under load isn't going to be my problem, just want to make
sure the tiles stick, although tile adhesives for wood all seem to be
the flexible sort anyway. There's conflicting views on to PVA or not
to PVA the ply first. To my mind, why PVA seal the surface first when
you want the adhesive to "soak in" a bit before it sets (or
crystallizes) to get good adhesion, but there may be something I'm
missing.

Any views?

David.

I went into this in detail recently for a cloakroom project - similar issues.

There were other issues of different substrates and after a lot of
looking I concluded that Ardex has the best range of solutions and
technical assistance from their helpline.

For plywood, their solution involves a two part binder/primer which is
applied and provides correct surface for a wide range of their
adhesives. Even after curing, the binder has a tacky surface for
some days and gives good grip even for very heavy tiles.

Ardex is certainly not the cheapest product range in the market, but it
is well supported in terms of technical help on what to use and it
works. Considering the cost of tiles and the time taken to get a
layout correct and do the job properly, the adhesive price is not so
important.