Battle with damp in the bathroom

[weazely]

I have a 1930's terrace house. Probably around 1955 an extension was put on at the back to accommodate a bathroom upstairs and a kitchen below.
The external wall (upstairs bathroom) has damp on the inside of the bathroom. I had the wall replastered and applied a weatherproofing solution to the outside. After a month the damp has come through again. I've managed to dry out most of it (radiator left on) but an amount still has damp coming through.
...its been an ongoing battle...
any ideas?

 

[Deluks]

Do you have any ventilation in the bathroom? Extractor fan or trickle vents in the windows? if not do you ever open the windows?

Wetness on external walls could also be caused by leaking gutters, ovespilling onto the top of your walls, and into the cavity if you have one.

 

[JohnD]

If you want to find out if it's condensation or penetrating damp, tightly tape a piece of clear polythene to the wall and see if the water forms on the wall side or the room side.

You can use aluminium foil as well, but of course you have to take it off the wall to look behind it.

Damp walls in bathrooms are usually condensation. lots of people have an aversion to ventilation, some will turn off fans and block airbricks.

//www.diynot.com/wiki/building:condensation_in_houses