THE GREAT DAMP ILLUSION - PART 2
Russell Rafton
Director at DRYFIX PRESERVATION LTD Yorkshire's Leading Damp and Timber Specialists / Director Coleman Diagnostics
It’s all just a bunch of hocus pocus, isn't it?. Well, in this article there’s no trickery or pokery just a straightforward explanation of how easily anyone can be fooled by an electronic moisture meter.
As explained in the first part of this article ‘The great damp proofing illusion – Part 1 –' surveying properties for damp related problems is a far more complicated subject than most appreciate and that’s probably due to the huge variety of potential causes, the complex routes that water/moisture takes through a building and potential masking effects. There’s no doubt that buildings are complex and rarely are two ever the same. Construction practices have evolved over time as to have the materials we choose to build with.?Most people would look at a wall and consider it just a wall however, when you break it down it’s far more than just a wall, it’s a foundation, a damp proof course, facing bricks, mortar, plaster, paint and skirtings, they all have different relationships to the surrounding structure and they’re all materials which react differently to moisture.
Every good building surveyor should have a decent understanding about material science and the various construction methods both above and below ground level. The role of most building surveyors is generally observational however in our industry, diagnosis is very rarely provided through observation alone. Very little can be understood from just observing the surface of a wall, accurate diagnosis generally requires some investigative work and testing of materials for moisture and contamination. The problem is that many of the instruments we use for assessing damp are not always fit for purpose, they can be very misleading and difficult to interpret.
I’ve lost count of the number of building reports I’ve read over the years which include disclaimers like “Dear Mrs Smith, Thank you for inviting me to survey your property for damp. During your survey I used an electronic moisture meter which when used on masonry takes readings which aren't quantitive therefore it cannot accurately measure damp in walls. My assessment is therefore merely an interpretation of instrumental readings and visual observations made during the survey” I mean really, what's the point? If a clients paying you to investigate a potential damp problem then surely for it to be accurate this should be conducted quantitively?.......
I often read peoples comments online on how finding rising damp is rare and how establishing the route cause is so important to provide accurate diagnosis, but in reality most diagnosis's are made via the interpretation of an electronic moisture meter. So just how accurate are they?
In this article, I want to explain just how easily electronic moisture meters can be misinterpreted even when combined with what most would consider clear and obvious symptoms of rising damp. Ask yourself in this situation, how accurate do you think your diagnosis would be?.......
This scenario is from a survey conducted a year or two back however it’s a good example of a perceived damp problem that was encouraged by misinterpretation of an electronic moisture meter.???
Our client purchased a period farmhouse on the outskirts of York which was in need of extensive refurbishment. They employed a trusted family friend and local interior designer to assist with the refurbishment and help recruit a team of contractors to undertake the work. ?The original farmhouse underwent an extensive refurbishment in addition to the construction of a new extension.?As part of the renovation works the building contractor installed a new damp proof course and re-plastered the entire property with what the client believed to be a lime plaster. Shortly after completion however the property started to display symptoms of a developing problem. The recently finished interior decorations started to spoil as the paintwork blemished and flaked from ground up - see image below.
Distressed internal decorations which started to spoil shortly after the renovation was completed.
Obviously, if you’ve ever endured the trouble and effort that any major home renovation requires, you’ll understand the heartache and distress this scenario would cause to any homeowner. The immediate concerns were towards the builder, the guy responsible for the renovation and damp proof course installation, but then wait, they discover the builder wasn't a damp specialist, there's also no paper trail of an initial damp assessment, no written specification and of course, no guarantee.
So, the client did what most homeowners would do in this situation, they brought in an specialist to assess the building and provide a diagnosis. The specialist’s survey as is all too often the case was conducted in a non-destructive manner, merely a visual inspection and appraisal of the property’s condition interpreted by readings taken from the walls with an electronic moisture meter. The results of their investigation disclosed that the property was suffering with rising damp due to poor building practices during the renovation.
Now visually you’d be forgiven to coming to this conclusion because there’s clearly evidence of distress to the internal decorations which appears to be migrating from the ground, symptoms you’d normally associate with rising damp. The electronic moisture meter when used in this region also screams aloud, alluding to the likelihood of moisture within the plaster and a problem with rising damp. But on its own and particularly from a specialists standpoint, is this evidence sufficient to diagnose rising damp particularly when there’s a likelihood of future litigation?.....
Electronic moisture meter revealing high readings when the spoiling plaster is tested.?
If you’ve ever wanted to know just how accurate electronic moisture meters can be at interpreting damp profiles, have a read of this article. When compared to disruptive gravimetric sampling, electronic moisture meters are highly accurate however, that doesn’t mean they cannot be misinterpreted even when all the symptoms suggest their right.
We were contracted to undertake an intrusive survey to investigate the apparent claims and accurately establish the condition of the walls. The British Research Establishment guidance document 245 “Rising damp in walls “Diagnosis and Treatment” suggests that whilst?electrical moisture meters do have a valuable role to play as preliminary surveying instruments, to obtain conclusive proof regarding the condition of the wall the most satisfactory approach is to take samples of masonry and plaster for analysis. As such, in addition to our general survey I was granted permission to extract samples of masonry from the problematic walls for moisture and contamination analysis.
In addition to our visual inspection of the property both externally and internally, skirting boards were removed from the most problematic walls, plaster was removed vertically exposing the brickwork and mortar joints and samples were removed from the walls in a methodical manner. These samples were then removed from site and processed over the following days in our in-house laboratory using the gravimetric process breaking down the sum components of each samples total moisture content. Each sample was then tested for mineral salt contamination.
For those interested here's an article that explains the process of methodically extracting samples for analysis whether that be onsite analysis using a speedy / carbide meter or offsite laboratory analysis.
The following images are of the samples extracted from the problematic walls for offsite moisture and salt analysis
领英推荐
The results of our lab analysis revealed that despite the walls visual appearance, the reaction of an electronic moisture meter and the prior diagnosis, that these walls were in-fact dry. Moreover, the walls weren’t just dry, they were bone dry with moisture levels which varied between only 0 – 1.1% free moisture content. This was a very dry building.
The distress caused to the plaster was the result of hygroscopic contamination and efflorescent surface salting. Our analysis revealed low but traceable levels of Chloride salts were found in the samples but high levels of ground water Nitrate salts were deposited throughout the walls. Hygroscopic contamination is in theory a form of dampness however, the moisture present isn’t the result of ground water or penetrating damp but from moisture within the air which is attracted to the surface of the wall due to contamination. Whilst hygroscopic contamination is clearly damaging to the plaster and internal decorations there's very little risk of decay or severe damage to the structure as would normally be associated with other forms of dampness.
Laboratory results from one profile taken within the building highlighting the absence of free moisture within the walls.
It's clear however that at some point throughout the buildings history that this property has been affected by moisture from the ground, hence the deposits of Nitrate salts. The cause however has clearly subsided. This doesn’t necessarily mean that an effective damp proof course was installed by the builder, in-fact quite the opposite. The reality is, the cause is more likely to be the result of an escape of water such as a burst water service or failed drain historically that’s been attended too.
In addition to the above, despite the understanding the walls had been plastered with lime, when investigated further we discovered again that they hadn't. In-fact the walls had been plastered with a combination of modern cement based renovating plasters and some gypsum materials. Unfortunately, the renovating plaster used is notorious for salting after application as the water mixed within the plaster starts to leave the walls surface. As such there is a likelihood that distress to the decorations had also been attributed to early redecoration prior to the plaster fully drying after application. The gypsum plasters simply should never have been used.
Inappropriate use of gypsum and cement renovating plasters during refurbishment
Whilst unfortunately for the client the likelihood is the spoilt plaster and decorations will probably need to be replaced however, the client will save considerable expense as replacement of the damp proofing isn't required. Furthermore they no longer have the worry that their property is rapidly deteriorating due to damp.
So the next time you're on a survey and your electronic moisture meter starts screaming, just remember in reality that damp meters are best used to disclose when a material is dry rather than when it is damp. Therefore my advice is, whenever there is ambiguity I'd always recommend you advise an intrusive survey with quantitive analysis from a credible contractor.
If you've made it this far, I hope you found this article useful and if you have any questions or queries please don't hesitate to get in touch.
Happy surveying
Russ
If you would like to learn more about damp diagnosis or surveying you may?also find the following articles useful:
The Great Damp proofing Illusion Part 1
Independent damp surveyor vs Contractor damp surveyor, which is best?
Five things you should know before you book a damp survey or repair
Russell Rafton - Dryfix Preservation Ltd Senior Surveyor
Dryfix Yorkshires Leading Damp & Timber Specialists
A 5 x Industry Award Winning Company with the Property Care Association.
Egerton Surveying Ltd
3 年Excellent article. Too many surveyors take on 'damp surveys' as a side line to their normal work and they are just not equipped enough to undertake intrusive inspections and tests.
..
3 年Great read ??
Managing Director at Richard Russell Surveyors
3 年Another interesting article Russell ????
C.Build E FCABE AssocRICS C.S.R.T. C.S.S.W. TIWSc. RSciTech
3 年A well-planned article young Russ, surveyors need to understand a ‘Conductance meter’ is only an indicator to inform there is or there is not an issue. It doesn’t give you all the answers. ?If your inspection is limited, i.e. a pre-purchase inspection, and you cannot provide a definitive answer for the elevated readings. You must recommend a further intrusive inspection is undertaken. It's not a crime to say, ‘I cannot confirm the reason for the readings, due to the limitations’ however it is a crime to make assumptions/ incorrect diagnoses which cost your client money.???? Time to go to the gym now.????♂? ??
Retired from roles in Health Research, Lecturing, Construction & Project Management. Now a Problem Seeker, Free Spirit & Prolific Tinkerer. Also a Wannabe Polyglot
3 年Thank you