Green Building Forum - The reliability of damp meters? Wed, 09 Sep 2026 00:09:18 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 The reliability of damp meters? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16922&Focus=287129#Comment_287129 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16922&Focus=287129#Comment_287129 Thu, 04 Feb 2021 11:47:12 +0000 kristeva
More damp shenanigans I'm afraid. I've learnt so much since my renovation began but the subject of damp, rising damp, and damp proofing is my biggest bugbear.

I've had a very nice builder at the house these last few days to fit some new joists in my kitchen and install a soil pipe. Today he dug out his moisture meter and took some readings on my walls downstairs, (all back to brick). The readings indicated damp, sometimes off the scale, at points beneath 1.2 meters, and some dry readings above. He firmly believes walls only need to breath one way and he wants me to bitumen tank the interior walls up to 1.2 meter and then dat & dab cellotex insulation. He reckons if I lime plaster the walls as soon as I move in and start heating the house all the moisture in the brick will be sucked in to the house!

I don't doubt the house has / has had problems but its a very complex issue. All the factors you could take into account are too numerous to list. The area has high clay content. I'm not sure the old screed floor in the kitchen is helping much. As I mentioned in previous threads I've already taken steps to remedy high external ground, installed new air bricks with regard to sub timber floor which was sweating, fixed faulty guttering, internal dpc injection (probably a waste of time).The house had last summer to 'dry out' but has not been heated this winter. I know there are salts in the chimneys which became apparent when I pumped a load of steam in most of the rooms removing thick wall paper.

Apologies for the ramble, I guess I'm debating whether I should take any stock in these meters? What are the alternative explanations? I've seen plenty of Peter Ward's videos showing these meters giving false readings, and I'm very interested in Tony's method of analysing/weighing brick dust (can't really afford a carbide meter). I need to make a decision about how I'm going to proceed as I'll be putting the house back together in the spring and I only want to do this once!]]> The reliability of damp meters? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16922&Focus=287130#Comment_287130 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16922&Focus=287130#Comment_287130 Thu, 04 Feb 2021 11:58:22 +0000 Dominic Cooney if you put a damp meter on those bits of wall at the moment it would go off the scale.

Once the heating system is up and running, the place has dried out fully, and the MVHR operational, then I fully expect no issues.]]> The reliability of damp meters? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16922&Focus=287131#Comment_287131 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16922&Focus=287131#Comment_287131 Thu, 04 Feb 2021 12:18:41 +0000 kristeva Posted By: Dominic CooneyIt's probably condensation at this time of the year with no heating. There are are still a couple of uninsulated bits of wall in our barn and they are dripping with condensation. I'm not worried because we have introduced gallons of water in the screed / laying a brick floor which still has to dry out. The only heating in there at the moment is a 1500w oil-filled radiator which is keeping it at about 10 degrees C depending on the outside weather.
if you put a damp meter on those bits of wall at the moment it would go off the scale.

Once the heating system is up and running, the place has dried out fully, and the MVHR operational, then I fully expect no issues.

Yes I thought some kind of condensation perhaps, even in winter. Or salts perhaps. And condensation would be more prominent at the base of the wall explaining the discrepancy in readings vertically?

My plan was / is to monitor and control moisture content within the house very closely utilising my dehumidifier when I move in.]]> The reliability of damp meters? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16922&Focus=287133#Comment_287133 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16922&Focus=287133#Comment_287133 Thu, 04 Feb 2021 12:36:06 +0000 Ed Davies Posted By: kristevaHe reckons if I lime plaster the walls as soon as I move in and start heating the house all the moisture in the brick will be sucked in to the house!Why would that matter, assuming the house is reasonably well ventilated?]]> The reliability of damp meters? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16922&Focus=287136#Comment_287136 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16922&Focus=287136#Comment_287136 Thu, 04 Feb 2021 13:07:13 +0000 tony
I drill a hole, collect the dust, weigh it, dry it, re weigh it and calculate % moisture

After damp survey said £8k of doc injection and replastering I found all walls less than 3.5% moisture and most less than 3% one wall 0.25% so I repeated the drilling to verify

Result was minor diy replastering £40 saving £8k

I don’t trust damp meters]]> The reliability of damp meters? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16922&Focus=287138#Comment_287138 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16922&Focus=287138#Comment_287138 Thu, 04 Feb 2021 13:32:07 +0000 kristeva Posted By: Ed Davies
Posted By: kristevaHe reckons if I lime plaster the walls as soon as I move in and start heating the house all the moisture in the brick will be sucked in to the house!
Why would that matter, assuming the house is reasonably well ventilated?

Well, yes, that's what I thought, provided it wasn't creating any damage to plaster/paint, my dehumidifier would soon mop it up. Its something you have to live with.]]> The reliability of damp meters? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16922&Focus=287139#Comment_287139 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16922&Focus=287139#Comment_287139 Thu, 04 Feb 2021 13:35:13 +0000 kristeva Posted By: tony‘Damp meters” measure electrical conductivity not damp

I drill a hole, collect the dust, weigh it, dry it, re weigh it and calculate % moisture

After damp survey said £8k of doc injection and replastering I found all walls less than 3.5% moisture and most less than 3% one wall 0.25% so I repeated the drilling to verify

Result was minor diy replastering £40 saving £8k

I don’t trust damp meters

I'm interested in doing this Tony, how are you calculating the % of moisture, and are you force drying the soil in an oven / microwave?]]> The reliability of damp meters? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16922&Focus=287142#Comment_287142 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16922&Focus=287142#Comment_287142 Thu, 04 Feb 2021 14:16:48 +0000 Dominic Cooney The reliability of damp meters? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16922&Focus=287149#Comment_287149 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16922&Focus=287149#Comment_287149 Thu, 04 Feb 2021 16:52:16 +0000 tony
(Weight of sample- weight of dry sample)/weight of wet sample x 100= % moisture]]> The reliability of damp meters? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16922&Focus=287150#Comment_287150 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16922&Focus=287150#Comment_287150 Thu, 04 Feb 2021 19:03:38 +0000 kristeva Posted By: tonyMy scales weigh to 0.001g and I dry samples in an oven at 120C for 10 mins in metal dish

(Weight of sample- weight of dry sample)/weight of wet sample x 100= % moisture

Thanks.]]> The reliability of damp meters? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16922&Focus=287151#Comment_287151 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16922&Focus=287151#Comment_287151 Thu, 04 Feb 2021 19:15:16 +0000 kristeva Posted By: Dominic CooneyIf you are really worried then I'm sure that some tanking slurries claim to be breathable even though they are waterproof. You paint this on to the bare brick in 2 coats, one vertical brush strokes, one horizontal.

A bit like 'Stormdry' I suppose, something like this:

https://www.buildbase.co.uk/cementone-tanking-slurry-20kg-10290-2841076]]> The reliability of damp meters? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16922&Focus=287163#Comment_287163 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16922&Focus=287163#Comment_287163 Fri, 05 Feb 2021 10:48:19 +0000 Dominic Cooney
Although Stormdry is completely different, it is a clear product that goes on the outside.

Cementitious tanking is grey or white and is usually used on the inside (it can be used on the outside for some applications) it is basically a thin layer of painted-on cement render.]]> The reliability of damp meters? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16922&Focus=287297#Comment_287297 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16922&Focus=287297#Comment_287297 Mon, 08 Feb 2021 16:48:14 +0000 Cliff Pope As said above, they measure electrcal conductivity and relate that to the dampness. The relationship varies depending on the substance being measured.

Needless to say, the bias enhances the readings which is why damp treatment companies love them.]]> The reliability of damp meters? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16922&Focus=287334#Comment_287334 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16922&Focus=287334#Comment_287334 Tue, 09 Feb 2021 08:37:33 +0000 Jonti Posted By: Cliff PopeIt's often said that the usual "damp" meters are in fact intended for measuring dampness in wood, not bricks etc, and give innacurate readings.


I have always taken the readings with a 'pinch of salt' view. I use them mainly for reading the moisture content in firewood where the difference between 14% or 16 % is not so big an issue.]]> The reliability of damp meters? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16922&Focus=287357#Comment_287357 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16922&Focus=287357#Comment_287357 Wed, 10 Feb 2021 08:38:11 +0000 kristeva Posted By: Cliff PopeIt's often said that the usual "damp" meters are in fact intended for measuring dampness in wood, not bricks etc, and give innacurate readings.
As said above, they measure electrcal conductivity and relate that to the dampness. The relationship varies depending on the substance being measured.

Needless to say, the bias enhances the readings which is why damp treatment companies love them.

Yes, this is what I've read too.

Its convenient for the damp companies that the top of wall will often read as 'dry' whilst the bottom of the wall (beneath 1.5 meters) reads 'damp' however. I guess there's a certain inevitability about this anyway, or bottom of the wall is colder, etc.]]> The reliability of damp meters? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16922&Focus=287363#Comment_287363 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16922&Focus=287363#Comment_287363 Wed, 10 Feb 2021 11:48:46 +0000 Ed Davies Posted By: JontiI have always taken the readings with a 'pinch of salt' view.Literally?

One sign of damp coming through walls is salt deposited on the surface which has dissolved inside then been left behind as the water evaporates from the surface. Salt water is much more conductive than pure water. Putting 2 and 2 together and making 3.14159, I wonder if the original salt content of the bricks affects damp meters much.]]> The reliability of damp meters? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16922&Focus=287373#Comment_287373 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16922&Focus=287373#Comment_287373 Thu, 11 Feb 2021 08:15:40 +0000 Jonti Posted By: Ed Davies
Posted By: JontiI have always taken the readings with a 'pinch of salt' view.
Literally?



:bigsmile:

Posted By: Ed Davies

One sign of damp coming through walls is salt deposited on the surface which has dissolved inside then been left behind as the water evaporates from the surface. Salt water is much more conductive than pure water. Putting 2 and 2 together and making 3.14159, I wonder if the original salt content of the bricks affects damp meters much.


It would make sense but this needs someone other than me to answer it :shamed:]]> The reliability of damp meters? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16922&Focus=287374#Comment_287374 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16922&Focus=287374#Comment_287374 Thu, 11 Feb 2021 08:48:56 +0000 tony