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Builder Challenges Use Of DPM

John Alcock on dispute over moisture levels

I RECENTLY paid a visit to a higher education building in northern England, which was a somewhat unusual project for us in that there was no discernible problem with the floor that had been installed.
However, the main contractor had questioned whether the flooring contractor was right to have used a damp proof membrane, and was consequently withholding payment until the matter was resolved.
Hygrometer tests at the start of the project showed a high level of moisture, and subsequent indicative tests of the subfloor at the time the levelling compound was due to be laid showed that it was still quite damp. So the decision had been made to install the damp proof membrane to ensure there were no problems with the floor later down the line.
However, the main contractor had decided to question whether a damp proof membrane was necessary because hygrometers had not been used to test subfloor moisture right before the DPM had been installed.
Their argument was that the floor would have dried out sufficiently by this point to not require a DPM, and so they should not be required to pay for this part of the work. In the absence of any absolute evidence to the contrary, the flooring contractor was having a tough time convincing them that they had done the right thing.
The problem here was that the flooring contractor was using his considerable experience to judge through indicative tests that a DPM was necessary, and installed one in the interests of making sure the job was finished on time without further visits to deal with damp problems.

You could say that he would have been better off using a hygrometer, but to get a true reading across what is a large building he would have had to spend the time placing and monitoring quite a large number of hygrometers across several days. If not, the risk is that you might be getting an unreliable reading of a particularly damp or dry area of the floor.
However, the time to do this would have removed the need to debate his work with the contractor later down the line.
The balance is between what experience tells you is the right decision, and making sure you provide the evidence for this.
Using a combination of indicative testing and hygrometers at all necessary points will give you the best results, as it will help to provide a clearer picture to the main contractor should they have any questions.
John Alcock is technical specifications manager at Bostik
T: 01785 272727
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This article has been reproduced from the Contract Flooring Journal website. You can find them at