Damp on a solid exterior wall in Victorian house

[Jupiter01]

My parents have an external wall which has damp across one of the internal corners. It goes from floor to the top of the wall. I cleaned it up last year and painted with mould resistant paint. They’ve kept the trickle vent open since then and had plenty of ventilation and heating in the room. There is a window and radiator on this wall too. Despite this, it’s turning black in places again.
It’s a solid wall and does not have a cavity. I’ve had a look externally and there are no obvious mortar gaps or places where water can be sleeping through.

Can someone please advise on how I can solve this please.

 

[endecotp]

Black mould is generally condensation from moisture inside the house, not water leaking in from outside.

Standard questions:

Extractor fans in bathroom and kitchen?
Do they dry washing inside?

 

[Jupiter01]

Thanks for the prompt response.
Extractors only kitchen and bathroom. Yes they do dry clothes in the house.

if I post a picture of the “blackness” would you be able to confirm if it’s condensation or water ingress please?

 

[endecotp]

Maybe.

 

[Jupiter01]

Will take a pic when I go around this week and post on here. Appreciated.

 

[endecotp]

I sometimes suggest getting a digital thermometer/hygrometer to measure the humidity.

 

[Jupiter01]

I can see screwfix do one for £15. Is this the type of device you had in mind?
What level of humidity is acceptable and what level indicates the proneness to condensation? Excuse the ignorance as I’ve never used one of these

 

[endecotp]

Search for “digital humidity” on ebay.

Note they take a while to respond to the conditions.

As for what’s normal, I suggest observing and trying to get a feel yourself. Right now my living room is 48%; bathroom after a shower (with a good extractor) maybe 80%.

 

[Jupiter01]

On this wall, I always get this blackness along one corner of the wall. Not the entire external wall. is that still symptomatic of condensation?

 

[endecotp]

The condensation will be where it os coldest and where there is least air circulation, so yes corners are typical, especially behind furniture.

 

[Jupiter01]

Aha...the other part of the exterior wall has an air vent. That makes sense...

thanks again

 

[Jupiter01]

Hi Guys,

Can I pick this up again please. I appreciate that this may be condensation but my folks are making a concerted effort to ventilate, etc. The net result is sporadic blackness on all external walls.

Excuse my ignorance, but I do all the things they do (cook, bath, dry clothes, etc.) but don’t have any black marks on any walls. I hardly worry about ventilation during cold months too. I am guessing I get away with it because I have a cavity wall construction whereas my parents have solid walls in their Victorian house? Can you please shed some light on this.

If this is the solution, I wonder if I should create a “second skin” on all these external walls. Is this a ultimate and perhaps extreme solution to this situation?

Thanks again.

 

[cwhaley]

You could batten out the wall, fill with insulation sheets and then plasterboard over (dry wall) or use insulation-backed plasterboard. That will stop a cold surface for the moisture vapour (and the mould spores) to settle on and form black spots.

From what you've said it'll almost certainly be down to lifestyle. When we moved into our house the upstairs front bedroom (North-facing) would get black mould on the bay window wall. We didn't dry clothes inside and put it down to water vapour from our breath at night when the heating was off. Sleeping with the window ajar at night wasn't comfortable so we did this during the day. In the end I did the first option mentioned above and since then haven't had any cold. I still open the windows to replace the air in the house.

 

[bobasd]

OP,
still waiting for the pic you promised 2 feb?

 

[endecotp]

Excuse my ignorance, but I do all the things they do (cook, bath, dry clothes, etc.) but don’t have any black marks on any walls. I hardly worry about ventilation during cold months too. I am guessing I get away with it because I have a cavity wall construction whereas my parents have solid walls in their Victorian house? Can you please shed some light on this.

If this is the solution, I wonder if I should create a “second skin” on all these external walls.

Yes, that’s called External Wall Insulation, and it will fix a lot of problems.