Damp patch has appeared - advice please (photos included)

batman2000

Hi, I recently had a new kitchen installed, which involved new floorboards and plastering throughout. But there’s a patch of plaster that has refused to dry since it was done 6 weeks ago, and after watching it closely it definitely gets worse when it has been raining.

I’ll try to summarise the main points:
- the patch measures about 50x30cm
- sometimes appears drier than others, with some salts too? I’ll attach photos.
- it’s an external wall under a window
- not noticed any damp here before, but it was previously wallpapered
- under the floor is dry
- the outside is rendered and there’s an odd vent (historic) to one side that was found when the plaster was removed (red circle on photos)
- some cracking to the render, but looks ok on close inspection 🤷‍♀️
- I had my boiler replaced 18 months ago and there’s a non rendered patch around the new flue which I’m not happy with, since there’s some greening of the plaster (top left on exterior photo)
- window was replaced 2 years ago

Could water from outside be tracking inside? What would be the first thing to look at? Do I need a damp survey, or not go that far yet? 

Yes, I know the outside render needs work, it’s on my long list of things to do. It might need to be prioritised now! Oh, and the house was built in the 1920s, this is the gable end. Thanks in advance.

Yesterday, before it rained overnight👇

stuart45

Is it cavity or solid? The render on the outer reveals needs to be finished.

batman2000

stuart45 said:

Is it cavity or solid? The render on the outer reveals needs to be finished.

Pretty sure it’s all cavity. The kitchen is partly extended, and the original outer wall was exposed when the floor came up. I need to get the reveals sorted, but could this cause the problem?

Also, as far as I know there’s no cavity wall insulation.

stuart45

Could be some rubbish fallen down the cavity and got caught on a wall tie when the old window was knocked out.

batman2000

stuart45 said:

Could be some rubbish fallen down the cavity and got caught on a wall tie when the old window was knocked out.

That would make sense. What a pain ☹️.

stuart45

It's only a guess. You need someone with a borescope to look into the cavity. The outside vent could come out now, and it's liner if there's one still in, then make good the wall.

Ganga

stuart45 said:

It's only a guess. You need someone with a borescope to look into the cavity. The outside vent could come out now, and it's liner if there's one still in, then make good the wall.

If they do this then they can inspect the cavity with the borescope at the same time.

Veteransaver

What is that waste pipe coming out of the wall for? Is it a WC sink or something?
We had similar a few years ago where the idiot boiler installer pulled the waste pipe from outside to make some space to put boiler pipes behind it. He yanked the pipe from the waste trap so for months all the water from the WC basin sink was going straight into the wall cavity.

markin

No silicone at the side of the window sill.

batman2000

Thanks everyone 👍. It’s a good guess though, @stuart45, and something to work with.

@Veteransaver, the pipe comes from the combi boiler that’s in the under stair cupboard next door… I checked, and it’s firmly attached!

ThisIsWeird

As said, that vent is ideally placed to give viewing access. You'll want it gone in any case.