Tiling a window sill.

[PHSUK]

Guys, please give me your thoughts on this subject. I've removed the original tiles from a window sill. The tile and plaster was about 15mm thick covering a cavity wall 1800mm x 200mm. I've got some expanded metal that I'm going to use so that I can cap the sill with new plaster to make it reasonably level again.

Now, my new tiles are about 8mm thick. I was talking to a trade counter employee and he suggested that rather than build up a topcoat of new plaster of say, 6mm, I should think of gluing down a piece of 6mm thick MDF. That will give me a perfectly flat base to which I can then cement the tiles onto. I'm happy to accept his idea and I know that you can lay tiles onto non-cement surfaces, but will that work on MDF?

It sort of makes sense to me to do what he proposes because I'm not a plasterer and I want to lay the tiles as flat as possible. Can someone tell me if the advice is sensible and if it is, what's the suggested approach for gluing the MDF onto a topcoat of plaster, and will any tile adhesive suffice for cementing the tiles onto the MDF?

[Honorary Bloke]

Well, you asked for thoughts and that's all I have. Have laid a lot of tile, but never tried to lay tile on MDF before.

For some reason, not easily particularised, I don't like the idea. Would rather see it laid on plywood or something else. If there is any chance at all that water can get near that MDF, it will swell and crack the tile joints. I admit it is a flat surface, which is desirable. Also don't know if the cement will like to grab hold of the slick MDF surface, but that can be remedied by a quick rough-up. Will be interested to see what others have experienced. I may be over-cautious.

[mic-d]

You would be better off using 6mm fibre cement board.

Cheers
Michael

[joe greiner]

If the tile is only for appearance, it probably doesn't matter. BUT, the tile sills I've seen around here (humid climate) are for moisture/mildew resistance. In that case, either solid plaster or non-absorbent flatwork. Cement board would be better than plywood; and MDF?: no, no, no.

Joe

[PHSUK]

Thank you gentlemen. The voice of reason is listened to. I will avoid the MDF route and look for the cement board.

Edit: I've capped the double cavity with expanded metal and render. What adhesive do you recommend I use to stick the cement board down on to the render? The same adhesive I'd use to lay the tiles on the cement board?

[mic-d]

Thank you gentlemen. The voice of reason is listened to. I will avoid the MDF route and look for the cement board.

Edit: I've capped the double cavity with expanded metal and render. What adhesive do you recommend I use to stick the cement board down on to the render? The same adhesive I'd use to lay the tiles on the cement board?

Yes just use a cement tile adhesive.

Cheers
Michael