Blistering paint & mould on external wall

[b21playa]

Hi all

Wondering if someone can help me out. I’ve started to notice paint blistering and black mould spot in a first floor bedroom. This is an external wall which is solid brick construction and render. There is a loft room above and the wall is dry.

Looking outside when it’s raining there isn’t any leaks from gutters etc. internal & external pic attached. There is some sort of lip on the external wall which can be seen, this for reference is about 3/4 way up the internal wall.

What could be causing this and any remedies? Could it be the paint has blown causing water to soak through?

Many thanks in advance

 

[23vc]

Condensation due to humidity inside and cold wall surface. Make sure all kitchens and bathrooms have working extractors etc…

 

[b21playa]

Thanks. Seems strange it’s the only wall in the house with the issue and there’s other external walls. Unfortunately bathroom doesn’t have extractor, but window is left open most of the day

 

[jj4091]

Is that the weather side of the house.The render looks pretty old to me. If it is definately a solid wall I would be thinking about having it taken off and redone. At the same time having external insualtion fitted before the renedering

 

[ree]

OP,
I dont see any significant render defects - although the render does look a bit cloudy in patches.
Heavy dark patches usually suggest water absorption.
The tiles abutting the render, do they have some kind of lead flashing thats been dashed with a little render?
If it is lead flashing then its been installed incorrectly, & moisture might be getting thro to the brickwork?

The interior pic : I cant see any blistering or bubbling plaster - can you do a more clear, detailed pic?
Centre high in the pic - are those similar dark spots?

 

[b21playa]

OP,
I dont see any significant render defects - although the render does look a bit cloudy in patches.
Heavy dark patches usually suggest water absorption.
The tiles abutting the render, do they have some kind of lead flashing thats been dashed with a little render?
If it is lead flashing then its been installed incorrectly, & moisture might be getting thro to the brickwork?

The interior pic : I cant see any blistering or bubbling plaster - can you do a more clear, detailed pic?
Centre high in the pic - are those similar dark spots?

Yes the render is old but doesn’t seem blown, I’ll need to get up to check closer when the weather is dryer.

I need to check the tiles abutting the render, not sure if there is lead flashing behind…been like this for a long time before I brought the place and not caused any issues but may need chipping out and new lead fitting, although this is much lower then the wall with the issue. Also seen a little mould in the adjoining room on the same external wall although not as bad.

I’ve taken some closer up pics

 

[ree]

OP,
Thanks for the new pics. What they show is definitely penetrating damp.
Your best bet would be to remove all the plaster from the wall back to brick - then render with a 3:1 sand & NH lime mix, and a Remedial skim finish. Dont use any gypsum.
Doing this will give you 20 to 30yrs free from defects - in the mean time you could investigate the external render etc?

 

[b21playa]

OP,
Thanks for the new pics. What they show is definitely penetrating damp.
Your best bet would be to remove all the plaster from the wall back to brick - then render with a 3:1 sand & NH lime mix, and a Remedial skim finish. Dont use any gypsum.
Doing this will give you 20 to 30yrs free from defects - in the mean time you could investigate the external render etc?

Thanks for confirming

I had plans to renovate the house but these are on hold due to funds going elsewhere unexpectedly. For now I’ll take a look at the render in the weekend providing it’s dry. If all looks ok and just blistered paint, would it be worth repainting in a breathable paint?

 

[ree]

OP,
"just blistered paint" is various chemicals coming thro, sometimes saturated, wet masonry - when it presents on your decorated surfaces its attracting ambient humidity moisture - & no matter what surface treatment you try it will continue to attempt to attract ambient moisture & keep presenting on the surface.
The decorators use blocking & various concoctions so FWIW why not try the decorators forum?

 

[b21playa]

Sorry I meant paint the external render, rather than the internal.

OP,
"just blistered paint" is various chemicals coming thro, sometimes saturated, wet masonry - when it presents on your decorated surfaces its attracting ambient humidity moisture - & no matter what surface treatment you try it will continue to attempt to attract ambient moisture & keep presenting on the surface.
The decorators use blocking & various concoctions so FWIW why not try the decorators forum?

 

[Ivor Windybottom]

I reckon painting the outside would be very beneficial. It looks like it's become porous.

Waterproof but breathable paint does exist, despite the apparent contradiction. I used Dulux Weathershield on our previous house right down to ground level even below the DPC, it gave a surface that the rain would run down but despite the wall being fairly damp in places nothing blistered off during the years we were there - unlike previous more plastic-like paint that had been blathered over it before, which had peeled off in sheets.

It may need pre-treating with an algae killer, and a vigorous brushing to remove anything loose. If it's powdery then Dulux do a Stabilising Solution that's really good, it's like a watery varnish that soaks in and sticks it together.

Is it a solid or cavity wall?

What's the lip above the first floor windows?

 

[b21playa]

I reckon painting the outside would be very beneficial. It looks like it's become porous.

Waterproof but breathable paint does exist, despite the apparent contradiction. I used Dulux Weathershield on our previous house right down to ground level even below the DPC, it gave a surface that the rain would run down but despite the wall being fairly damp in places nothing blistered off during the years we were there - unlike previous more plastic-like paint that had been blathered over it before, which had peeled off in sheets.

It may need pre-treating with an algae killer.

Is it a solid or cavity wall?

What's the lip above the first floor windows?

It’s a solid wall.

I’ll get some algae killer and look at paint. Was thinking of sandtex microseal

Not sure what that tip actually is, not sure if it was out there as a bead when the loft was done (in the 80s) for the render

 

[Ivor Windybottom]

I did look at Sandtex too, I only picked Dulux as I preferred their version of bland beige, the Sandtex at the time was too yellowy. I'm sure both are absolutely fine.

Was it a hip-to-gable conversion? I'm hoping it's not the original timber wallplate that's been built on top of.