I am renovatiing bathroom. I will have 2 walls painted and two walls tiled with ceramic tiles. The old bathroom had rubbish tile effect panels glued on. These were removed to reveal a white surface that I have not been able to identify. It is bright white, unpainted and a bit like artex. It is quite a thick layer and may have lime plaster underneath, and brick under that on 2 walls and hollow block on the other two. It is not painted and just spread on any old how. There is evidence of dot dab shapes in areas so it might be some sort of tile adhesive? It is tougher than plaster. Any ideas what this is? My plasterer who also said he was a tiler has gone over it with carlite bonding and multifinish on the 2 walls I will paint and gone over the other 2 walls with carlite bonding to even it up for tiling. One of which he has only put a thin layer on the top half. Also note that the carlite was mixed with a small bag of mortar cement to make it go off quicker. The walls I plan to paint went off OK (it was all done 3 years ago so has had plenty of time to cure). one of the carlite only walls has dark patches which look like it may have absorbed some moisture possibly from the air. I have investigated this to discover that carlite is not ideal for tiling onto. I do not wish to hack back to the brick if I can avoid it because I dont know what kind of dust might be created by the white stuff. I don't think there is asbestos but who knows?

There will be a bath with shower over in the tiled corner. The painted walls will not have direct exposure to water but the air will obviously be very humid.

My questions are:

1. Will the painted walls be OK or is carlite plus multi finish plus paint unsuitable for a humid bathroom?

What can I do about it? e.g paint with SBR and then paint over with bathroom paint?

2. What do I do with the walls I want to tile? Hack off and then cement render? Can I get away with a slurry of multifinish and SBR then skimming it with finishing plaster mixed with SBR? Is there some other waterproof coating I can apply? Will it be OK with heavy tiles stuck on?

3. I have seen sheets of thin blue polystyrene for sale which are covered in grey cement on each side. Can I cover the carlite with these? They look a bit flimsy but I guess they are OK once tiles are on??? If so, how do I attach them to the wall?

I really want to do the best possible job here and have a leak proof shower bath without cutting corners so would be grateful for advice from some REAL proffessionals.

I will use mapei cement based tile adhesive and mapei grout.

Many thanks

you could cover the walls with cement boards if the tiles are really heavy(what tiles are they and what are they made of?)Alternatively you could fix plasterboard to the walls and tile onto this .

If the toilet is well ventilated then you shoulodnt have a problem with moisture....maybe a good idea to get a quality fan fitted also.


Let us know what tiles you are using and you will get more advice .

I plan to use ceramic tiles that look like travertine. I haven bought them yet but i'd imagine the dimensions to be somehting like 40X25X5. What is the composition of cement board? I havent come across that. Is it the same as the polystyrene with cement/fiberglass mesh covered board?

see below

http://www.bpindex.co.uk/manf.html?id=2678

If he mixed carlite bonding ( Gypsum based) and portland cement.....that is a disaster waiting to happen.......Gypsum and cement do not mix......They react together causing Ettringite failure....this could be a quick reaction or may take a long time but deffo not to be mixed together....The Ettringite can blow off the tiles...

To add extra gypsum to portland cement is crazy , it will increase the chances of Ettringite formation....

I think you need to think again about hacking it off.....

The white stuff you mentioned could be dry wall adhesive spread over the wall to build it up. I agree with Dave about mixing cement with gypsum not reccomended even by British Gypsum. If you hack off could'nt you dot and dab with plasterboard.

as soon as i saw the thread, "carlite and tiles " hit my straight away, deffo a no no no imo, go for the hack off and have a blank canvas to work from!

i am with everyone else,hack it off then board the walls,but i would`nt be tempted to cheat and try to board to the walls the way they are,disaster/ accident waiting to happen in my opinion


Jimmy