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Help please!

I'm about to tile in my bathroom, above a bath (upto the ceiling), to make a kind-of shower enclosure.
The walls have been perviously painted, looks a bit shinny.
How should i prime(do i need to?) the walls before tiling.
I'm going to use Unibold tile adhesive, and a separate black unibold grout.

I read somewhere that PVA in not a good idea.
Should a score/sand the paint?
The bath has already to fitted, and i cannot afford to get the walls replastered.

any help would be amazing - I really don't want to do this twice!!

I tiled on to painted wall 30 odd years ago in the house we were in then. In my naivete I just used a course sandpaper and stuck the tiles up and they stayed in place for the 10 years we lived there. I think the test is the weight of the tiles you intend to stick up as the ones I used back then were the 4" square tiles that were common at the time. Clearly the bond will be stuck to the paint and if the paint is well on then your tiles should hold okay. PVA is not a good idea in damp places as when it gets wet it reactivates and the tiles could come loose. Also ready mixed adhesives are not the best as hand mixed powder base are best.

I am sure some of the tilers will be on later to give proper advice on what to do in this situation but in the mean time let us know what size tiles you will be using. Also you can have a chat with BAL technical who are very good. http://www.bal-adhesives.co.uk/technical/faq

Hope this helps

DWD

You will probably want to do a 'Tape-test', get some masking tape (someone might correct me, but i think there could be different strengths ??, get a low end strength one) and stick it on, leave it on for a while and then pull it away, if that is enough to pull off the paint then you will need to just strip the paint off (sand paper or scrapper), no point getting them re-plastered, as they would only need to strip the paint off as well.

If the paint is on there nice and strong then it will be fine to tile.

brilliant thanks!! - that was super quick.

will try the tape test

but to answer the tile size question - they are brick shaped - 10x33cm

If you do want to be doubly sure then just sand it off, you can rent an electric sander for not much money, will do the job in no time and that way you will be certain you are going onto a good surface.

If you sand back to the plaster then you can prime it.
(something like this - http://www.bal-adhesives.co.uk/products/primer)

Tape test - Use a strong tape such as gaffer tape. Like the previous poster said, leave it on for 30 mins or so then rip it off. If no paint comes off with it, then score the surface diagonally about 50mm apart and tile away. If the paint does peel off, then I would recommend you get it all off with a scraper. If they are ceramic tiles, you could use a ready mixed adhesive. BAL Whitestar and Mapei Mapeigrip D2 are both good. I wouldnt use Unibond myself. If they are non-porous such as porcelain or glass, or a natural stone, I would use a cement based adhesive such as BAL Single Part Flexible or Mapei Adsilex P9. If using cement based, you should prime the walls with BAL Prime or Mapei Primer G.