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Approximately 1 year ago we had a wall treated with damp proof course injections (silicone I believe) and we then rendered with a mixture including a relatively strong mix of good waterproofer.

After a few months we started to see what appeared to be a recurrence of the damp on two wall corners.

We've now had the company that injected the chemical DPC round and they have found that the plaster where this damp is showing is quite soft. They therefore claim that our plaster / render is deficient as this is coming through from the wall still having moisture in it, and that "good" render / plaster would still be hard and holding this damp in, even if there was rising damp there, so as it's soft then it has to be the plaster / render.

The image below shows this issue. I find this hard to take (partly I'm sure because of the time and money invested and at risk from their assessment) but also because it looks so much like it's damp rising through the corner of the wall.

Should I accept that this is residual moisture, 1 year after treatment, and that our render is definitively at fault?

Edit: to clarify this is a wall between the kitchen and entrance hallway, approx 1m from external wall. Original issue is rising damp - house is from early 1900s so built without a DPC. We are near a river and water table is relatively close.

enter image description here

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  • Where is this wall located? What's inside of it? When you've got a water issue you've got to go to the source - a surface fix (damp proofing??? never heard of it) isn't going to suffice. – The Evil Greebo Sep 26 '12 at 11:55
  • The wall is between the entrance hallway and kitchen, around 1m from outside wall. No piping inside the wall etc. All damp is presumed to be rising - we live fairly near a river and the water table is not far down, additionally this is an early 1900's house so it wasn't built with a DPC... – Timbo Sep 26 '12 at 12:01
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    Ok, in that case the "bad plaster render" sounds like a crap excuse. – The Evil Greebo Sep 26 '12 at 12:08
  • Thanks - that was my feeling, but they tried very hard to claim that unless your render is fully waterproof then you will get issues until the wall has dried (well over a year apparently). But it looks like it's rising up the wall to me... – Timbo Sep 26 '12 at 12:29
  • Well,I'll defer to someone else who might know more about plastering - I'm a dry wall user myself - but it certainly sounds like BS to me – The Evil Greebo Sep 26 '12 at 12:43
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"Deficient" render? That is a line of bull. Your use of damp proof course and render makes me think you are UK based. If so, you should have a guarantee of several years for the damp course work, and if so you should demand they fix the problem as they clearly missed a spot. Residual moisture? Don't make me laugh. They need to do fresh moisture measurements and to re-course the areas that still show high moisture content.

At the same time look at your exterior brickwork in the area of the damp and make sure that your pointing and exterior render isn't blown. Also, when it rains make sure your guttering is piping the rain down to the ground properly.

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  • You're quite right about the UK. Thanks for the input - that was my suspicion... – Timbo Sep 26 '12 at 19:58
  • Good luck @Timbo, I hope they do the right thing. – GdD Sep 26 '12 at 21:04
  • Thanks @GdD - I'll endeavour to update with the outcome! – Timbo Oct 1 '12 at 11:58
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There are two things going on here. One is that the damp-proofing is clearly deficient. If it wasn't, then you wouldn't see moisture here. End of story, right? Well not quite, because if the plaster is getting soft from rising damp, that's a sign that the wrong plaster was used. Probably something gypsum-based, which is a bad choice for an old house with residual issues with rising damp. These types of buildings were originally finished with lime plaster, which is not water-soluble the way gypsum plaster is. It may get wet but it will not soften or disintegrate. Lime plaster would be the correct plaster to use in your house, not gypsum plaster with some kind of synthetic waterproofing agent added.

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