I am converting a small understairs room in a 30's Semi into a small bathroom (it used to be the "Coal Hole" in years gone by!).
The side walls are both brick, in reasonable condition, although there is some loose and powdery mortar. Both walls are damp - I can see small beads of moisture on the surface of the pointing. The brickwork has been painted with a thin coat of emulsion paint at some date long past. The paint adhesion to the brickwork seems pretty good.
I am planning to tile the walls, but it seems to me that I will need some kind of waterproofing before applying the tiles. Can anyone recommend a suitable product, preferably one that could be applied directly to the brickwork, as I am very tight for width in the room and cannot afford any solution that would add more than about 12mm to each wall?

Many thanks

Welcome,
As a company we can recommend this firm highly for quality and assistance....Gaz
Internal Tanking - Waterproof Membrane

there is no point tanking or membraning any wall if its not dry,the moisture will have to come out first,and then stop the source of the moisture.
you then would have no need to tank the room unless you really wanted too.

Thank You for your helpful replies. I think it will be difficult to eliminate the source of the damp as it is rising through an old and rather ineffective bitumen damp-proof course which has degraded with time.
Even if I could insert an effective damp-proof course, there are adjacent areas of the walls that I cannot get to to treat, so moisture would just travel across from the untreated areas.

Have a look at this site:

Wet Basement Waterproofing, Finishing & Flooring, Swimming Pool, Deck & Concrete Crack Repair, Roof & Industrial Floor Coating
Should be of some help, but I don't know if they have any dealers in the UK.
They are about the best method.
Second would be to first dry out the area and saturate it with a sodium silicate solution.
But given that it is bricks and the silicate works by reacting with the calcium in the portland cement or mortar the bricks would still allow water to seep.
Maybe it won't cost too much to get some of their product shipped to you.