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.
Graham Coleman's Moisture meter profiles
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.
Dry Rot.
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!
Graham Coleman.
Beware those who do not note ‘possible interpretations’. The surface moisture profile of rising damp is replicated by underfloor condensation (timber floors), leaks (all floors) and other problems.
Thanks for looking in Peter,
I agree to an extent. – Damp diagnosis is a specialist job and requires anyone doing it to consider all potential factors, which could give the profile. However, as a damp specialist I am expected to give my client a diagnosis, based on my survey. Most of the time I’m happy to give one and I rarely need to add any caviats like - possible – may be – could be or possibly.. Customers don’t like wishy washy reports so I try to avoid this.
There are times though, when one is stumped or the evidence does indeed point to something ‘not quite right’ – in these cases I agree that further investigation is needed. It’s not always straightforward.
I like overview patterns as they help you form a framework for investigating many things. Grahams work is very useful tool. I will put it in my brief case. I believe it is important not to mix fact with opinion and sometimes on initial inspections it is not possible to undertake tests to categorically define a cause as a matter of fact so possibilities have to be used to explain risk. It may be that further tests are recommended and the balance of the do nothing option explored. I assume “Dry rot” does casework which involves destructive testing until a result is certain and so he is right that all his comments can be expressed as factual. Surveyors must be careful not to sound authoritative by stating opinion as fact.This is where the word possible is useful. The client can expect your skill to assess a scale of risk in such cases so some measure should be found so as not to render comments valueless.
Hi Geoff,
Nice to hear from you. I’m a big fan of Graham’s profile table and I’m glad you like it too, so simple and very intuitive.
I’m wary of getting too hung-up on semantics, where opinion and facts in reports come in; the spectre of the court room has a lot to answer for. I see too many survey reports which are so full of caveats and hedged bets, that their value to clients is dubious, to say the least. These reports are often the most expensive and lengthy ones too.
Giving my clients good information is the goal, but they shouldn’t be expected to understand all the technical issues (though some are fascinated by it and I like to indulge them when they are). Perhaps they may not have the time or inclination to want to ponder these things? In receiving my report, the last thing most need is a list of ‘maybe this’ and ‘maybe that’s’.
The diagnosis ought to be direct and specific; this can be given, without destructive or invasive testing – most of the time…………… in my opinion.
I’ve talked about this with Graham and others, who confirm that in over 95% of cases, a damp diagnosis, which is made using a moisture meter, common sense, experience, profiling and some methodology is correct, when checked later, using destructive lab methods.
Should we hedge our bets in a report and burden clients with risk analysis, and the pros and cons of this and that, for less than one twentieth occasions, when profiling may be wrong?
Of course, the above ratio assumes that all users of electrical moisture meters know how to use them, which is the rub and the reason I support the damp diagnosis group’s aims. I bet that the 1:20 ratio can be improved on and maybe reduce to nearer 1:100 if we all work together. I wouldn’t expect such a low success rate with my own meter or the majority of surveyors like yourself and other damp diagnosis group members, who are enthusiastic and serious about their work.
waht do the numbers in the table represent? they are units of what?
Hi Jack,
The numbers are relative only. They can be described as ‘per cent’ when the meter is being used in wood, because most meters are calibrated for average softwood. In masonry the same scale is used but if % is mentioned it is termed % WME – that is wood moisture equivalent. So that we if you see WME you know what the meter was reading – you don’t knoe how much water was there. In damp diagnosis it is often the relative distribution of moisture which tells a surveyor the most, rather than the exact moisture content.
In fact the exact moisture content is rarely important; 3% may be excessive in one type of plaster/brick and be acceptable in others…
Thank you for looking in, I hope the article helped you.
Bryan