Damp - "Damp Meters"

I know that "damp meters" are much derided here as they don't accurately say if there is damp in a wall or not but, as they *are* used by surveyors, what level of dampness do they normally say is something that's a problem or are they just a bunch of rip-off artists and will say that the walls need doing if the thing beeps at all?

Thanks.

Reply to
Ed_Zep
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Would it not be better to ask at what damp levels a problem really does occur, ie symptoms of a damp problem occur? Yes there is false positive diagnosis.

NT

Reply to
meow2222

Damp meters are very accurate, it is the interpretion of their output which is usually dodgy. The output from the meter together with a visual examination of the situation is route to an accurate diagnosis. If you get say five different damp companies you will get five different opinions.

Reply to
avocado

Damp meters are calibrated for timber, and can not (should not) be used to determine moisture content of any other material. Generally timber in a typical house will have moisture of around 5-10% but up to 20%. But it varies widely - even through the day

They can be used to roughly check if a part of the room has more moisture than other parts, but this involves a thorough check of multiple parts of the whole room, in order to ascertain if areas have more moisture than others. But this is a comparative test, not a true measure.

If placed on the surface of, or slightly pressed into plaster, you can expect an elevated reading, but this is more often due to surface condensation. The surveyor will then angle the meter so that you can see this. I've known of 'surveyors' breathing on a section of wall first just to get a slightly higher reading to show the occupant.

Coincidently, we had a solicitors letter last week and a surveyors' report alledging damp at a property. I surveyed it, and the occupant said that their surveyor just placed the meter on the wall and showed her the reading which was high. So "she must have damp".

When I explained how a dampness investigation should be done, she was quite annoyed that the 'surveyor' could not substantiate his claims, and had not done a proper survey. But the sorry part of it, was that the surveyors fees and solicitors fees would be paid out of legal aid funding, so they will not mind if they have not done a proper survey and the claims are false.

dg

Reply to
dg

how can they be accurate if the area of probe in contact with the wall is uncontrolled, as it is with 2 pointy bits on a rough surface. how can they be accurate if building materials have resistance of their own which adds to the current the damp meter measures how can they be accurate if salts present in materials change the conductivity of the water present and hence the readings

In wood yes. theyre fine, but on masonry theyre just not measuring damp, theyre measuring resistance which depends on several factors.

NT

Reply to
meow2222

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