MDF in a bathroom

[ceramic man]

Hello

I would be grateful for a definitive answer on this. I am creating a tile picture to go in a large bathroom. The picture will not be near the shower and not splashed with water. But obviously there will be some moisture in the room. The picture is to be constructed from waterproof ceramic tile, on MDF, and grouted with Mapei waterproof grout. The edges of the MDF will be tiled and grouted too. And grouted where there are gaps at the back. What is the best way of waterproofing the back of thre MDF so all sides and edges are waterproofed? Or, am I barking up the wrong tree entirely and should I work on marine play or similar (the picture is to be 128x128cm - can I get marine ply, aquapanel etc this big?)

What adhesive is recommended for this?

Many thanks in advance for all help.

 

[gcol]

Bal would recommend their Bal Bond SBR, but you can seal the sheet back with something like an outdoor woodstain. It's not too important what you use, so long as it's protecting the wood and limiting the rate that moisture can be absorbed.
You can readily get ply in 1220mm x 2440mm sheets (8' x 4' in old money) so that'll be a bit shy (width wise) for what you want. Personally, I'd prefer ply though.

 

[Jasonb]

If you are going to use MDF get the moisture resistant one that has a green tint. But WBP ply would also be suitable.

In this case I would suggest sealing the back of the board as there will presumably be nothing to hold it flat, then use BAL Mosaic fix which is about the only one they say is OK for MDF.

You can get the ply in "large press" size 3050x1525 but the MR MDF will only come 1220 wide.

Wedi board at 1200x2500 is another option that will not be affected by moisture and would be the best choice if you can live with the 1200mm width.

Jason

 

[ceramic man]

thanks very much for the above answers. MDF is not OK then, but with the above answers in mind, which of the following is best to to resist mositure for use in a bathroom (not in or near the shower/bath, not to be splashed with water) and how they compare price-wise, approximately for a sheet around 1220x2500mm:

Marine Ply
WBP plywood
Moisture Resistant MDF
Exterior MDF

(to take waterproof tiles on one side and around the edges, fixed with waterproof adhesive and grouted with waterproof grout)

many thanks

 

[Jasonb]

See my reply on your double post.

For any of these surfaces make sure you use a flexible adhesive and flexible grout.

Jason