Electronic Damp/Moisture meters and foil backing; an example

For those with even a passing interest in damp surveying, reports of electronic moisture meters being ‘fooled’ by all sorts of strange phenomenon are bound to surface. Salts are one such condition, foil backed wallpaper being another.

I find that the most of these are overblown, with too much emphasis given to these quite rare and easily detected conditions. The video is from a one of this week’s surveys where I needed to take foil into account – enjoy.

Conductivity moisture meter over-reading due to foil

A high reading caused by foil backed wallpaper.

 Chemical testing and salt analysis 2

Other methods of measuring damp – the Chemical moisture meter (seen here with salt kit)


It’s true of course, stick your meter on a metal object and it will go mad, despite the obvious lack of water.  Stick it on a dry salty wall or timber though, and no such panic will ensue; despite the salt content, the readings will usually be in the moderate to low zone; water is needed for the salts to conduct sufficient current to read as very damp; When salts are in solid, rather than a liquid state, the interface between the crystals forms gaps, which the current cannot leap over; fill these with water or liquidise the salts and hey presto – damp.

Salt contaminated timber with low moisture meter reading.

Electronic moisture meter testing salt contaminated timber in a roof in Harrogate


Anyway, this post is just a short example of what your damp meter readings are likely to look like, where metal foil is detected. The house is an old Victorian semi in Leeds, West Yorkshire and I am on site for a pre-purchase damp and timber survey for my client.  High readings have been reported and the survey is justified by this and due to the age of the house and it’s obvious lack of any TLC in the past.


Moisture meters and metal foil – facts for users


So as you saw there, it would be quite difficult for any half-competent surveyor not to realise that there was something not quite right with the moisture meter; even when there are obvious damp sources near by. From my view this is something of only passing interest, but there are some who seem to have a real ‘downer’ on electronic moisture meters and the foil issue is often stated as a negative, (along with salts, carbon contaminated clinker and such)  cited as a reason to doubt findings which are based on these instruments.  This is a complete misrepresentation of the facts, as they apply on site, in the real world.


Low moisture meter reading compensated for foil backing

Low damp meter readings from a wall covered by foil backed wallpaper, after adjustment.


The moisture meter is a reliable and valuable tool, but like any other it takes some skill to interpret the results.  Use a meter daily and very soon anyone can become quite proficient at moisture profiling and damp diagnosis. Add some training with the Property Care Association, maybe the odd rummage through my blog and then sit and pass the CSRT examination and you’re well on the way to becoming a specialist .

In truth, most experienced surveyors like me, who own chemical moisture meters and salt analysis kits, tend to use them very rarely; the electronic moisture meter is just so convenient and reliable – chemical methods are infrequently needed.

Dry Rot

PS – look at the speedy gauge and the salts test……notice anything?


  1. Robert Deary says

    Again, nice to see the video which opens the eyes to the untrained/unaware.

    It does go to show that they can be misused just like any piece of kit in the wrong hands, but in the right hands shows how to interpret the information correctly.

    I did see the manufacturer of the Speedy Meter and salts test if thats what you mean. Some people would consider that to be a conspiracy.

    Keep up the good work.

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