Moisture meters

I'm sure there'll be a wealth of knowledge about this. I need a meter to test a couple of wall areas in a house I'm looking at. It'll need to be a sensor rather than pin type as I don't want to leave any marks. Prices range from a suspiciously cheap tenner on ebay and maybe £20-25 at known retailers up to hundreds. What do I need to know and will an inexpensive one suffice? If I find any serious concerns I'll walk or consult a surveyor.

 

i noticed 2 pin marks behind a picture recently ... one way to hide those marks !!

 

They all work on conductivity (actually resistance, I suppose, although one is the reciprocal of the other) between two electrodes.
The numbers they produce are meaningless except in comparison using the same meter.
You will get different readings across a surface (mark/prick-free), and within the surface/first mm or so.

Anyone used a bog standard DMM? It will give a reading but in ohms, and you'd need a simple jig to keep the distance between probes, constant.

Personally? I'd trust far more to common-sense and direct observation.

In a building - modern (post 1950's or so, wide) cavity walls are dry barring something having screwed-up somewhere. All else are damp to some degree. That said, my parent's place was built with cavity walls around 1900 and was dry (in very dry East Anglia).

 

How old is the house and, is it single or double skin? And is it on concrete foundations with a UPVC damp proof course?

 

Hmmm - must keep an eye out for one of those - I have only ever seen thick polythene, slate and blue brick DPCs. uPVC seems a poor choice in comparison.

What has that got to do with the price of fish?
Concrete foundations should be a long way below any DPC and have no effect. They are also very modern - endless houses into the 1960's were built with little or no foundations of any kind, and they are very often dry.

 

I have one that’s very good for telling me when the wood is seasoned sufficiently to burn. Less than 20% moisture is ideal. That’s probably not too helpful in context of the OP. Sorry.

 

Is a moisture meter different from a hygrometer? Used to have something of the kind inside a box for cigars. It looked like it should not cost more than 10 Euro and was pretty sensitive, at least in the 40 - 80 % range. I also remember something about horse hair.

 

A hygrometer is a word GENERALLY used for an instrument that measures atmospheric humidity, that is, air.

In which case, cheaper versions usually use some hygroscopic material or other to produce movement of a lever, or whatever, to provide an indication (a bit like pine cones opening and closing due to RH changes). Expensive ones, at the extreme, generally use a thin film capacitor and software.

 

The house is early 70s with cavity walls. The areas in question are on the inside walls. I'm thinking that damp can just as easily come from inside the house as the outside.

 

Thank you!

 

I have a 1960 bungalow - the extreme corners suffer minor condensation as they are just simply cold/the coldest spots - inesacapable.