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Damp Proofing

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I have had the lower wall hacked off and damp proofing inserted. The top half of the wall is now showing signs of damp. I have been told this is because new plaster is meeting old and the damp has to come through somewhere. Is his correct?
Have I any recourse with either the builder or damproofing agent? It was done approx. 18 months ago.

6 Answers from MyBuilder Damp Proofing Specialists

Hello None_92

18 months ago!!! Really?I agree the moisture will need to escape from somewhere but for 18 months:(There is a drying time for the new Render/Plaster as the wall is still releasing moisture upto a year or so after completed works,so this hinders decoration etc.But to still look or be wet sounds wrong!!!!

May i ask in relation to the wall in question is the external ground higher than the internal floor level?
Is the wall solid 114mm or 225mm thick or does it have a cavity?
Did you decorate this wall/walls too early or even paper it?

Just trying to work out why its still damp.Sounds like the plastering is doing its job and keeping the damp out,but is the DPC defective? If rising damp is getting past the supposed new DPC then it may be new moisture reaching the old plaster.

How high did they repaster and did they go 300mm past last signs of salt marks/band as you need to loose all contaminated plaster as this can cause continuous issues.

If you are local to Essex i would be more than happy to have a look and offer a free Survey to try to determine the problem for you.Failing this call them back and express your issues and cocerns.They may even take a sample of the plaster to run tests to determine if its contaminated etc.

Good Luck.

Scott Cannon.


Answered 10th Jun 2011

How high up did they remove existing plaster, normally min 1m/1200.
I have never heard that where old plaster meets new plaster has to let the damp come through.
If it was done properly you wont have any damp come through.
Best to get an independent damp proof company out to check it over and advise you what action to take.


Answered 10th Jun 2011

yes,both above are right,no damp should be reaching your original plaster,damp should not be passing your newly injected damp course.


Answered 12th Jun 2011

What's on the outside


Answered 18th Jun 2011

I assume that a damp proofing company carried out the works , If so they should come back and re-inspect , they should have informed you of the make of DPC they installed
and therefore you can call the manufacturer and they should have an area rep . The only occasion you get moisture on top of the damp works is where the new plaster
above sits onto the new render which contains an integral
waterproofer and therefore the water in the plaster cant penetrate into the render, this sometimes causes a slight
line , this should have dried though by now as it usually only lasts approx 3 months.
Either way you need to get an independent expert out to take a look.


Answered 21st Jun 2011

SALT BAND!!! This is more often than not the reason why you get damp at the new/old wall plaster junction. A dpc is injected to prevent further rising damp occurring. It does not eliminate the damp that is already present within the structure. This has to evaporate over a period of 9-12 months (depending on the thickness of the wall etc). As the new wall plaster should contain a waterproof additive, the evaporation of the current damp in the wall is inhibited so it will rise through the capillaries of the structure until it reaches an area where evaporation can take place, which is usually the new/old wall plaster junction. Because it contains the hygroscopic salts found in rising damp, these will absorb moisture from the air and thus become damp. To eliminate this, the area of damp wall plaster (i.e. salt band) should be removed and replaced with new. (If you require further information or confirmation of this answer, speak to any CSRT surveyor) Kind regards, Sarah


Answered 11th Jul 2011

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