I deliberately didn't get the plasterers to skim over the walls in our ensuite because I wanted to ensure we didn't end up with mouldy plaster in years to come. The room is as small as you can get with a shower, basin and loo. The walls are concrete block and brick.

The tiles I'm planning on using are large so would benefit from a flat surface. Do I parge the walls with a cement/sand mix first so the blocks are airtight. Are tile backing boards a good idea for providing the flat surface for tiling? If so, would you recommend sticking on the wall with drywall adhesive plus screws?

My aim is to make the walls airtight, provide a flat smooth surface for tiling and not have mould problems in the future. The room does have ufh and will be permanently ventilated with mvhr.

Typically, on masonry construction the walls will be rendered with a sand/cement render - the quality being described as roughed for tiles, usualy float finished- I'd agree that they shouldn't be set or skimmed.

If the plasterer is any good, the wall flatness will be as good as any glued on boards - or better actually.

Regards

Barney

If you want a DIY job as opposed to calling in a plasterer these may be worth a look:
http://www.dukkaboard.com/index.php
They are available up to 8' x 4' and coupled with wall floor junction sealing plus floor sealing should give you the perfect "wet" room surface prior to tiling.

In my mind the most crucial thing is for the floor or tray upstand to up behind the wall covering. = fail safe (cant leak)

Dukkaboard are very similar to these:-

http://www.pcsboard.com/products/boards/construction-boards/

or Marmox or Jackoboard, and others like Schluter. All I understand are a high density polystyrene core with a polymer cementitious mesh covering.

I need to build up some existing floor levels for tiling, and I looked at using them instead of poured screed laid on a bed of thin coat tile adhesive. It'll certainly be less mess and I think cheaper than say a 25mm screed.
I've seen some ridiculous prices quoted for various makes but you should be able to pick up a 1200 x 600 sheet of say 12.5mm for about £7-8 + VAT less if you buy a lot.
I think they really come into their own for things like curved surfaces or sloping boards to create falls.


Mike

I think I'm going for the PCS version, AFAIK they are the only ones made in the UK.