Sometimes a damp survey will require a destructive survey, before any form of damp proofing is recommended.
When using a moisture meter for damp diagnosis you need to profile up the wall from the skirting board. A high reading in the skirting board will tell you that something is going on (above 20%), and further investigation is needed. I personally dismiss any readings in masonry below 25% wme even though the damp meter is beeping away and going red. I’ve found all my results from Bre Digest 245 using my tested meter that I have cross referenced tell me otherwise, others do vary!……And this is how you should test for quantitative damp diagnosis.
So this particular house had high readings in the skirting board which had evidence of woodworm frass on the floor. The readings on the wall were well within the limits of a dry wall, so why was this mis-diagnosed as rising damp? This is when a damp specialist surveyor that wants to find out what is going on will be worth his weight in gold.
The picture below shows a dry wall and a damp skirting board (see readings)
On removing a section of skirting board this is what I could see, even though I have seen this problem many times, I had to remove it as I wanted to show my client the exact cause.
The picture above shows where the skirting board has been cut out, you can see that the red brick is visible at the bottom of the wall, this is damp and the plaster is dry. So whats the problem? The damp course has been drilled at the first available mortar bed as close to the floor as possible, so this is probably up to 100mm from the solid floor (beneath this is damp).
What the contractor has failed to do is apply a floor and wall joint, this is either a cementitious product or a liquid membrane that overlaps the floor by 150mm and up the wall to just above the injected damp proof course. So by emitting this, the red brick below the damp proof course has stayed damp.
Why did the the floor and wall junction joint get emitted? I don’t know, this is a very common problem that I see every week, nearly every specification that I see from other damp contractors they never allow or carry out floor and wall junction works. Its either as they don’t know, or anything to make a few more quid!
So this is essentially causing the dampness and high readings to the skirting board which has caused the woodworm infestation. The woodworm infestation doesn’t need any treatment because it is a wood boring weevil infestation, wood boring weevil doesn’t need any treatment, simply remove the moisture source and there will be no further infestation.
As I enjoy thermal imaging, I thought I would include a picture showing the difference in temperature in the below thermal blended image.