Dampness on bathroom walls ?

[mayaknew]

Recently I've been getting loads of black dampness on my bathroom walls . When I spray it with bleach and wipe it it mostly goes away but doesn't leave a small mark (probably one that I see because I know is there)

It's quite a lot right up two of the walls (bare walls painted white) I've been here 6 years and this has only been happening the last few months .

Any chance someone might know what is causing it ? Or do I need to get someone in to have a look ?

That should say "does leave a small mark"

Are they external walls? Could you have a problem with your roof/guttering?

Has anything else changed? Are you having more showers/airing it less afterwards?

Yes they are external walls . And now you mention it the internal walls are fine . No nothing else has changed that I can think .

what sort of extractor fan have you got, and how long does it run?

I don't know it's got a wee pull cord on it ? It's always running on a low setting (you have to stand on the toilet seat to turn it off completely) then when we are going in showers etc we pull the cord to make it go faster .

OK then. Condensation tends to cause black mildew near the ceiling, all the way along the top of external (but not internal) walls. It will be worse in cold weather.

If you know anyone who smokes, ask them to hold their fag near the extractor, and see if the smoke is whisked away. On a frosty day, you may be able to see steam coming out on the outside.

If it is properly ventilated, it might be that you have a spilling gutter on the outside, especially if it is an older house with non-cavity walls. Have a look on a rainy day. A gutter or leaking pipe may give a damp spot, extending downwards in an oval. If you can attach some photos it would help, of both the inside and the outside walls.