WBP or Marine Ply

[TheOldFellow]

What's the difference?

I need to support a shower tray, is 18mm WBP OK?

Thanks. R.

[NT]

[John Rumm]

About £40 a sheet probably. Genuine marine ply is frighteningly expensive.

You may find 12mm is actually more appropriate - if its a stone resin tray you need to allow about 12mm for the layer of bedding mortar as well. If the ply is too thick you can run into difficulties with some waste fittings not being long enough to go through the tray, bedding, and 19mm of ply.

As long as the ply is well supported, it wont sag.

[TheOldFellow]

This seems to suggest that WBP will be OK for my application, since it will not be continually immersed, being under the tray (MX ResinLite

45) which I will be fitting using Dow-Corning 785, and then tiling down to. I plan on a double silicone bead at the wall junctions, one behind the tiles and then another visible on top. My WBP comes from a reputable local building suppliers (Atkinsons in Cockermouth), and it is stamped (and I have a sq meter of 18mm layin' aboot).

I'm beginning to really like the diywiki, I'll have to remember to check it before asking in future.

Thanks, R.

[David WE Roberts]

doesn't mention 'exterior grade ply' which I have bought previously for various outdoor uses. I think this is the stuff used on large public building sites to fill in the barrier between people and the interesting stuff, and also to fill in broken shop windows etc.

Could this be 'shuttering ply'?

[John Rumm]

Exterior generally implies WBP, and shuttering is the cheapest form of WBP.