The Damp Industry Con & The Con Surrounding the Damp Industry Con

Hand held electronic moisture meters have a part to play in any credible damp investigation process.
Hand held electronic moisture meters have a part to play in any credible damp investigation process.

The Damp Industry Con


There is a business that regularly posts videos on Youtube, very alarmist video’s about how the damp industry are conning people and about how the hand held electrical moisture meter is the tool of choice that allegedly provides the evidence that properties are suffering from rising damp. One might be forgiven for thinking that the poster of such material was qualified with a construction related degree and Chartered membership on a relevant professional body, but despite describing himself as being ‘uniquely qualified’ to survey for damp, he is in fact completely unqualified at even the most basic of levels. He will use words like ‘heritage’ or ‘conservation’ or ‘breathability’ because those are the good buzz words that prove that he must know what he is doing and even claims to be an expert in old properties. As has been pointed out before being a self appointed ‘expert’ does not make one qualified;  we’ll call this salesman, Mr Heritage. One of my clients recently contacted this salesman with a view to carrying out a survey on a 400 year old property. When they appointed us they asked if we knew Mr Heritage and were surprised to find out that he was completely unqualified.

Mr Heritage will often refer to the damp meter as a ‘salt’ meter, presumably to let us all know that they don’t actually measure damp, which of course is true, but to claim that they only measure salt levels is absolute nonsense and dare I say it, a con, because this particular unqualified ‘whistleblower’ is also trying to gain public trust and business from false information. Essentially, we have the public being made aware of one con on the back of another con used as supporting evidence.

A Credible Damp Investigation Process

Here again is a professional damp investigation process flow charted out. Electronic moisture meters and calcium carbide both fit into the process though clearly you could not diagnose rising damp by using a moisture meter in isolation; thermohygrometers have no part to play in this investigation process related to testing for moisture at depth in masonry! Anyone who thinks that electronic moisture meters do not have a valuable part to play in the investigation process does not have an efficient investigation process and probably doesn’t understand the process.  It is rather simplistic to state that electronic moisture meters were not developed for measuring moisture in masonry and whilst this is technically correct, modern professional moisture meters are sophisticated instruments specifically developed for taking relative moisture readings in buildings and a whole range of materials, including masonry. It’s all very well to sensationalise the idea that moisture meters are being used  to con the public and that they are not meant for use in masonry but the fact is that they are! It is simply that they only measure relative readings and the assessment of relative readings  forms a clear part of the investigation process. It is the operator at fault and not the tool!

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Damp Investigation Process Flowchart






Damp Experts

I am not a fan of the damp proofing industry and believe that the vast majority of damp proofing industry operatives are completely unqualified to be diagnosing damp of any sort. This is the great damp industry con because there is actually no qualification available to become an expert in damp diagnosis but a construction related degree should be bare minimum starting point, simply because the starting point of any damp investigation is the assessment of the building technology and build type. If there is an issue with regard to public education, it is not with regard to sensationalising the ‘alleged’ uselessness of damp meters because in fact, they are far from useless and form an important checkpoint in any professional damp investigation. A professional site practitioner would know this. It is old news to say that these instruments have their limitations and can’t be used in isolation to diagnose rising damp, every professional practitioner should also know this.

The lowdown on calcium carbide testing

Calcium Carbide is a critical & accurate site test
Calcium Carbide is a critical & accurate site test

We next arrive at another wrong that needs to be corrected… I have spoken to a number of damp ‘specialists’ who do not believe that calcium carbide testing forms any useful part of a site damp investigation process. I have also seen this viewpoint in print and this is taught on the back of three falsehoods:

  1. Calcium carbide can not be used to measure total moisture content (TMC), rather it can only measure capillary moisture content (CMC), which is meaningless.
  2. Calcium carbide testing is not accurate enough or  less accurate than gravimetric (Oven drying) testing.
  3. Calcium Carbide testing is too ‘invasive’ and not suitable under most survey circumstances.

As with lots of industries we can often make the mistake of assuming that trade bodies are industry regulators when of course they are not. They are there to promote the interests of their members and in turn generate income for themselves. If a trade body were to promote the truth, which is that calcium carbide is a valuable tool in the diagnostic process, then the incredibly high incidence of incorrect diagnosis for rising damp would be quickly addressed. Of course, this would immediately mean that the damp industry would need to shrink to a fraction of its current size, because as I consistently say, rising damp is incredibly rare. The damp proofing Industry body generally promote the viewpoint that rising damp can be diagnosed with a visual inspection, a moisture meter and ‘common sense.’ Since common sense isn’t all that common we prefer to adopt the academically accepted view that in fact moisture meters can not be used in isolation to diagnose rising damp, no matter how much common sense the user has.  Ironically, where I do find rising damp, it is generally ‘induced’ rising damp caused by inappropriate damp proofing works.

I’ll deal with each of these three points relating to calcium carbide testing in turn:

  1. Calcium carbide can in fact be used to measure total moisture content (TMC) but I quickly found out that the academic process used to determine TMC is long winded and diagnostically insignificant. The idea here is that TMC can only be arrived at after first understanding capillary and hygroscopic moisture content in the wall being tested. The simple formula is CMC-HMC = TMC            Surprisingly, masonry walls have a low vapour resistance of around 7, to help contextualise this, loose fibre insulation has a VR of 1.  What this means is that internal masonry walls will naturally absorb some moisture from the atmosphere and and reach a level of moisture equilibrium with the internal environment. This absorbed moisture is the natural hygroscopic moisture content (HMC) within that wall. The HMC is generally very low, in fact, usually so low as to give a zero reading when tested with calcium carbide. We have never yet, in hundreds of damp surveys found a HMC that was at significant levels that would affect the survey outcome or the final conclusions and recommendations for work. To establish HMC, you would simply find a dry area of wall using your electronic moisture meter in scan mode. Despite them being referred to as ‘salt’ meters, in fact they are excellent for determining where damp is absent rather when where it is present. Once you have scanned a dry area, test this area with calcium carbide and that gives you your HMC. If you don’t yet agree that HMC is an insignificant part of the process for determining total moisture content then try it for yourself over the course of a few surveys. That being said, if I am doing expert witness work, then I test for HMC because this is the academically accepted process. It is simply a pointless exercise for the vast majority of damp investigations.
  2. As with all damp investigations interpretation of your results is critical. If you get a high capillary moisture content of 3% at wall base and it has caused decorative spoiling then you need to take action. This is despite the fact that BRE 245 tells us that 5% is the accepted level at which remedial action may be required. Of course if I ran a laboratory that carried out gravimetric testing of masonry samples then I might also promote the idea that oven drying is the only acceptable method for testing total moisture content but it simply isn’t true. Even BS5250, which is the COP for the management of condensation in buildings promotes calcium carbide as being almost as accurate as oven drying. In my opinion, oven drying is unnecessarily time consuming, expensive, and will provide results that are diagnostically insignificant when compared to tests results obtained with calcium carbide. Ironically, oven drying isn’t a method we see used by the damp industry, they generally do no diagnostic work but cite the superiority of oven drying over calcium carbide as an excuse for not doing either test. However, to the damp industry, diagnostic results are irrelevant since they generally deal in management solutions and not cures. In other words, they want to sell you waterproof plastering systems and chemicals, so if your only interest is in selling products that hide rather than cure the damp then why bother doing diagnostic work?
  3. If we carry out calcium carbide testing then the it is usually because we have decorative spoiling and remedial works are already required to the wall being tested. There is therefore no significant issue with drilling a wall and we have only had one resident refuse or not want invasive testing over the last ten years. That was simply because they were ill and didn’t want the noise of the drill. The only other reason we would carry out CC testing is where the wall appears sound and unspoilt and despite recording low surface readings for damp, we obtain very high scan readings for moisture at depth. Other visual evidence might indicate that waterproof plasters have been applied by the damp industry and we suspect a damp underlying wall dammed in with renovation plasters. In these circumstances we have an obligation to inform homeowners that their damp has simply been temporarily hidden rather than cured.  Screen Shot 2015-09-26 at 11.48.13The idea that calcium carbide testing is too ‘invasive’ is an idea heavily supported by Oxley & Gobert in their book, Dampness in Buildings. This isn’t a book I’d recommend, it contains a great deal of inaccuracy and biased opinion  and perhaps the fact that Gobert is Honarary Life President of Protimeter Plc has some impact on the only  published dissenting view I have found with regards to the otherwise generalised opinion that calcium carbide testing is an excellent site diagnostic tool. Worryingly, this book is heavily marketed by most firms who sell surveying equipment but it is outdated and technically incorrect in a number of areas. Good damp investigation is about having good process, a good range of diagnostic tools a a strong knowledge of building technology and a thorough understanding of the principles of damp investigation.


6 responses to “The Damp Industry Con & The Con Surrounding the Damp Industry Con”

  1. Lee Newsome avatar
    Lee Newsome

    I had a surveyor use a protimeter which gave back a high reading and he deduced that my house was damp. On drilling into the brick work the samples were bone dry!!
    I have worked in the timber industry for 30 years and personally don’t believe that these instruments that are widely used by surveyors and damp treatment personel can or should be used in determining moisture in brick as it is a completely different material in its structure

    1. Joe Malone avatar
      Joe Malone

      Hi Lee,

      Whilst I understand your comment, I have to say that I disagree. It’s simply that they shouldn’t be used in isolation to diagnose damp. Hand held moisture meters are a critical part of the damp investigation process, and if not used, how do we know where to test for moisture at depth? As I always say, these meters are a great tool for detecting the absence, rather than presence of damp, where low readings are obtained, we can usually believe them, but where high readings are obtained, we move onto the next stage and test for moisture at depth, because false positive readings for damp, are a very common issue. Moreover, it may just be that the plasterwork is damp, due to condensation, whereas the underlying masonry is dry.

      Regards. Joe Malone

  2. Sam avatar

    I have just had a speedy test done in my living room and it read at 14 what does this mean please

    1. Joe Malone avatar
      Joe Malone

      Sam, BRE 245 (The guidance document) states that walls can be considered as being damp with a total moisture content of 5% or more, so at 14%, your wall is extremely damp. I would hope that moisture profiling was also done to establish where this moisture was coming from?



  3. Adam avatar

    Hi Joe,

    Either I am reading it wrong or something is a bit off with the above calculation….CMC-HMC=TMC.

    CMC = Capillary moisture content
    HMC = Hygroscopic moisture content
    TMC = Total moisture content

    Surely then, TMC relates to the combination of CMC + HMC?

    If a wall is damp due to suspected salt issue, then the process you describe above to determine HMC wouldn’t work as the HMC you really need to know is of the damp bit, not the dry bit?


    1. Joe Malone avatar
      Joe Malone

      Hi Adam,

      No, all walls are deemed to have a normal hygroscopic moisture content (HMC), and therefore this is subtracted from the capillary moisture content to give us our total moisture content.

      The negative effect of salts are over stated, because it helps sell replastering systems.Academically, salts analysis is used purely to verify the presence of rising damp, and doesn’t factor into moisture calculations.

      Regards. Joe

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