Damp Issues

darreng1983 · 23 Dec 2018

I’ve been renovating a small (3x3m) extension and have noticed damp patches on the concrete floor in the two corners furthest away from the house. They only appear during or after rain, and dry up afterwards. The adjacent plaster is dry, although the boards don’t touch the block work due to dot and dab. I’ve dug down to the concrete foundations and all the pointing looks ok.

Construction wise, it is single skin block work (I know this is the biggest issue), rendered to just above the DPC. A DPM is also present.

Any ideas where this could be coming from? And is there anything I could do to prevent it?

Thanks

Darren

Hi,

Notch7 · 23 Dec 2018

Unfortunately close ups arent very helpful, if you able to post an overall shot of the extension from the outside it would help make sense.

I guess thats screed in the pic thats damp?

A liquid dpm might help stop it getting through to your floor finish

darreng1983 · 23 Dec 2018

Notch7 said:
Unfortunately close ups arent very helpful, if you able to post an overall shot of the extension from the outside it would help make sense.

I guess thats screed in the pic thats damp?

A liquid dpm might help stop it getting through to your floor finish

Thanks for your reply, I've just taken these photos of the two corners.

These show the over all build.

John D v2.0 · 23 Dec 2018

I'm surprised you can get something that meets building regs with a single skin, but judging by your ground levels in the earlier photos the water might be splashing up off those paving slabs onto the wall and penetrating through. Based on the current photos actually it looks like the whole corner is wet beside the window, is it coming down from above? When you say extension presumably just an external conservatory/sun room rather then open to the house?
You say it's when rain happens, if it happens at other times and the room is heated it could even be condensation behind the plaster board.

darreng1983 · 23 Dec 2018

John D v2.0 said:
I'm surprised you can get something that meets building regs with a single skin, but judging by your ground levels the water must be splashing up onto the wall and penetrating through. When you say extension presumably just an external conservatory/sun room rather then open to the house?
You say it's when rain happens, if it happens at other times and the room is heated it could even be condensation behind the plaster board.

Yeah it was a conservatory of sorts, I've replaced the roof with tiles and insulation and has been signed off by building control.

It only gets damp when it rains, no other times, so I don't think it is condensation.

Notch7 · 23 Dec 2018

darreng1983 said:
Yeah it was a conservatory of sorts, I've replaced the roof with tiles and insulation and has been signed off by building control.

It only gets damp when it rains, no other times, so I don't think it is condensation.

If you are sure its damp penetration, then its either rain soaking into the wall and working down to the screed, or its the soil getting damp and travelling up through the concrete oversite and into the screed.

darreng1983 · 24 Dec 2018

I think I'm going to paint the bricks below the render with some water proofer, and if that doesn't sort it, I'll use some liquid DPM over the areas that get damp

Bit of a bodge I guess, but short of building a cavity wall, it'll have to do

catlad · 24 Dec 2018

You could screen one of the corners with a tarp and see if it makes any difference when it next rains.

darreng1983 · 24 Dec 2018

catlad said:
You could screen one of the corners with a tarp and see if it makes any difference when it next rains.

Good idea thanks, I'll do that before I do anything else as at least it should eliminate damp going through the render/above the DPC.

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Damp Issues

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