DIY Doctor

Damp Stains

Postby Summerill » Thu Jul 19, 2007 12:43 pm


About 1 month ago I had a damp proof course (dpc injections) installed to the ground floor of my 1800's terraced house. We have been advised that we need to have the plaster hacked off and replastered as there are damp stains to some areas of the walls. I have been looking at products such as Thompsons Damp Seal which say they cover the stains, allow the moisture to evaporate and that's it. If this is the case why do I need to get the plaster hacked of the walls and replastered? Does this product not do the job at a fraction of the cost? I am hoping someone may have some advise they could offer on this dilemma?

Thank you!
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Simply Build It

Postby Perry525 » Thu Jul 19, 2007 5:21 pm

It is normal for a property of that time to have damp walls - no DPC.
They will have been damp since the property was built.
Did they need "fixing?" How did you decide?
Anyway, if the injected DPC is a success and the damp is not in part caused by rain and/or condensation the walls will dry out - this may take some time, as they do salts that have been in the walls since they were built will leach to the surface and cause stains.
Damp will normally rise to about 4 feet/120cm from the floor. If it is boxed in it will spread both sideways and upwards.
It is normal to remove the plaster to at least 4 feet and to render with cement and a top coat of plaster.
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Postby Summerill » Fri Jul 20, 2007 12:45 pm

To decide if they needed fixing we had a range of quotes, the majority recommending damp proof course injections followed by hacking off plaster and replastering. A couple of quotes just advised on replastering the areas where the stains are.

My thinking (and this is only logically) is that if we have treated the source of the damp then the plaster will dry out as they tell you the brick work does. The DPC should prevent any more damp rising up the wall. In which case the marks are just stains, and should not get worse as in theory they should be dyring out and, if treated with a damp seal we can carry on and redecorate without the need (and expense) to replaster?

I guess this is my question? Or am I completely barking up the wrong tree??
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Postby dcmoore » Sun Jul 22, 2007 7:49 pm

I have been in the dampness business for over 30 years and in my direct experience cutting off the source of rising damp by inserting a chemical DPC is less than half the job - the residual dampness contains 'salts' (some already in evidence in your stains) and these will remain in the wall forever. Unless a special barrier render backed plaster or a membrane system is used, the moisture attracting 'salts' will keep on surfacing and causing damage to your decorations.

Do not apply water repellent treatments in this situation - they are a complete waste of money.


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