Electrical Moisture meters for damp diagnosis – oh yes.
A thing that raises an eyebrow amongst some independent surveyors is the way we so called ‘specialists’ seem happy to diagnose rising damp, or damp of any kind, using nothing more than our eyes and a conductivity moisture meter.
“Ha; I can get a reading off my fingertips or my head; I must have rising damp” scoff some.
It’s true; these meters give only a qualitative measurement. The figure is accurate, only in it’s relativity, to the previous reading – or the next. It will tell you if your head is dryer than your hand; even by how much; proportionately.
These meters cannot provide a true moisture content in masonry, plaster or indeed anything but wood; which many of them are calibrated for (and even then it’s only an approximation).
I know I’ve blogged on this before and you know all this already. But Graham Coleman has kindly sent me the table he drew up a long time ago and which all CSRT and many CRDS qualified surveyors will be all too familiar with, (though there’s always room for a quick refresher, hey lads)?
It’s the sad case that when I follow other surveyors on properties, where these meters have been used and where sometimes, diagnosis has been given; I often spot a problem. It’s the position of those little pairs of holes, which the meter pins leave behind; on the wallpaper and the paint. The thing is; they are almost invariably, just above the skirting board, maybe pearceing the plaster, an inch or two up and perhaps spaced a metre apart or more. They are rarely anywhere else.
What could these readings possibly tell the meter user?
Not much, I’m afraid. Maybe they were all very low? Well I suppose that’s something. Or maybe very high? Well there’s damp of some sort isn’t there? Oh dear; I fear they didn’t actually provide anything really usefull, from a damp diagnosis point of view. What a waste.
Look at Graham’s table; it’s the damp specialist’s version of Mendeleev’s periodic table; there may be gaps and things to add, but I think it’s a simple work of genius.
I know that reciting the periodic table doesn’t make you a chemist. In the same way, printing this and sticking it under the lid of your survey tool-box will not make a specialist of you. But is there a decent chemist who never checks the periodic table, just to check he’s on the right lines?
So, when surprised by that sudden, ardent bleeping from your meter, what to do? Take a look at the readings and then work away – up and left and right and maybe the skirting, (not relative), and repeat. Think and look at the table. You’ve already looked outside and all around the area, so do that again. Then when you’ve finished, you will almost certanly have a very accurate diagnosis.
My thanks go to Graham for the table and his tireless work in drumming all this stuff into my thick head over the past few years. Please remember that this is Graham’s work, not mine. If you want to copy it for your workbook, toolbox or thesis do so, but make sure Graham’s name stays on it please.
If you would like to use it commercially – ask Graham first; it’s his.
Oh, I forgot – nothing is ever written in stone; this is Graham’s take on his table…….
“These are some possible interpretations of moisture meter readings recorded at low level from walls; all have been validated by sampling and subsequent testing. There may be other interpretations of the same patterns but these are likely to be the most commonly encountered. There may also be other patterns but these are likely to be less common; for example, low level surface condensation might give a pattern similar to pattern ‘A’ but it will be purely a surface effect and highly likely to be obtained only during the colder months of the year. The important feature when using an electrical moisture meter is to record both vertical and horizontal patterns – one needs to interpret the pattern, not the actual figure. Remember, the patterns given are ‘possible’ interpretations.” Oh yes, pattern ’F’ – the damp-proofers nightmare – no work!