Rising damp

[jacdaniels]

Hi guys,
I have finally got to the source of a damp problem under the stairs. Basically the plaster, (and then once that was removed), the render, was damp. It only appeared on the surface and once I removed it I found what is shown in the attached photo.
There seems to have been a damp proof course put in at some point, (there are brown plastic caps along the length of the wall), and that seems to be holding as there is no damp above it in the brickwork.
The problem appears to be the brickwork below it, (which is below external ground level) is damp and the render and plaster over the top was sucking up this damp causing a surface damp problem.
Having found the problem, I have no idea how to fix it or work around it. I need to re-render and plaster the wall but I assume the exact same problem will happen.

Can anyone advise on how to prevent this happening?

(I have already dug well down and put a DPM against the external wall, backfilled with stones for good drainage, concreted over and installed a concrete fillet to keep water away from the house).

Thanks for all your help.

Untitled

• jacdaniels
• 4 Feb 2009
• 2

 

[^woody^]

Apply a waterproofing coating below DPC prior to plastering

Dryline

Water proof render

 

[kevintaylore]

You appear to have a classic case of "bridging" of the damp proof course. It is normal practice to coat the bricks below the DPC level with a waterproof coating (bitumen, tanking slurry etc...). Normally this coating will continue up the wall a couple of inches above the DPC injection holes to create an overlap. Additionally, the plaster should be cut short of floor level - the resulting gap being covered when the skirting boards are replaced.

 

[WabbitPoo]

If you are cutting the plaster back to above the dpc what function does the bitumen perform? Surely it just seals in the moisture and, dpc or no, it will come out somewhere? Innocent question from an interested non-builder!

 

[kevintaylore]

If you are cutting the plaster back to above the dpc what function does the bitumen perform?

To be fair, it probably isn't necessary, but it is always seen as good practice. I suppose it might have a function in protecting the skirting boards from damp which could otherwide cause them to rot.

 

[^woody^]

If the wall is coated up to just past the DPC, then damp wont get through, and so plaster can be taken down past the DPC, and the skirtings wont be affected.

But this could introduce a different probelm in the form of condensation due to the bottom section of the wall being colder than the wall above as it is wetter. And this could be mistaken for rising damp again!

 

[PerryOne]

The best permanent way to deal with this is, buy a cream dpc on e-bay and insert your own dpc at ground level, and take it down below the floor, making sure to drill down through the verticle lines of mortar at an angle of 45 - 50 degrees.
Damp rises through the air bubbles that were entrained in the mortar when it was mixed, the cream stops that.
Then plaster over.

 

[jacdaniels]

Thanks for all your helpful replies. I will take it on board.