Dryfix News

How one paragraph in a BRE digest is used to dismiss thousands of damp related insurance claims.

May 20th, 2019

All posts, Damp / Rising Damp / Damp Proofing /, Surveying


This article my ruffle a few feathers however I believe it’s a topic well worthy of discussion.

How one paragraph in a BRE digest is used to dismiss thousands of damp related insurance claims…….and how contractors may also assist in this process.

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So, do you know what this device is?…………………………………….

If you do great, you’re half way into understanding how this piece of equipment is often used to defraud clients out of thousands of pounds on damp related insurance claims.

If you’re not sure what this device is, it’s a form of moisture meter used to measure moisture in samples of masonry. Here’s a link to an article explaining what it is and how it works //www.dryfix.net/blog/damp-diagnosis-calcium-carbide-meter-speedy-meter/

The calcium carbide meter or speedy meter as it’s also known gets a lot of bad publicity from those in the industry who know the devices limitations. Like most damp meters the calcium carbide meter has it’s limitations but none more really than any other. Yes, it’s disruptive, yes, the results only measure total moisture content and yes, once the samples taken are destroyed, nevertheless they do have their place.

Chances are however, as a client you’ll probably never see one, and if you do, the likelihood is it’ll be during a revisit after a complaint about damp reoccurring. Most contractors will probably own one although it’ll likely spend the majority of its life on a shelf in the back office gathering dust.

So why is it that this device is more often used to disprove damp on an insurance claim rather than prove damp during a survey? The answer to that question is, I have no idea! We have one and use it daily, although at Dryfix we cross boundaries between restoration and preservation, therefore in the aid of diagnosing moisture and monitoring buildings during drying it’s an invaluable piece of equipment. For many in the preservation industry its often seen as a disruptive, time consuming and expensive alternative to the electronic moisture meter. 

The scenario often occurs where treatment of a wall has been undertaken which involves re-plastering. After a period of time spoiling reappears and the wall starts to resemble symptoms similar to those observed before the repair. Low level discoloration and spoiling of the reinstated plaster. A contractor is instructed by the client/insurers to inspect the condition of the work under the guarantee and provide an opinion. It is only now, the contractor chooses to withdraw his now trusty calcium carbide meter.

So, the plaster is spoiling but the results of the trusted calcium carbide meter reveal a moisture level of 3%. The contractor states the wall is dry, the repair is successful, and the wall is no longer suffering from the effects of rising damp. The cause must be salt contamination of the plaster, it’s failed or something similar.

Salting plasterwork

Now failure of the plaster maybe the contractor’s responsibility or it maybe passed onto a subcontract plaster, perhaps the clients own employed plasterer. Needless to say, it’s no longer his responsibility.

So, who ever said 3% MC content were dry? Well no-one but the BRE Digest 245, goes someway to aiding this impression.

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One paragraph written in the 1986 BRE Digest 245 reads as follows:

If the found moisture content (MC) is less than 5% at the base it is unlikely that the wall is severely affected by rising damp”.

There you go, a perfect get out clause for any contractor wanting to disprove the possibility of rising damp during a re-visit. This paragraph however, doesn’t actually state that a wall with a MC% of less than 5% is dry, it simply states the wall is unlikely to be affected by severe rising damp.

So, the contractor now disapproves the claims leaving the client in a salty mess.

Here’s a prime example from a recent insurance claim I visited. A contractor has already visited the property and undertaken some tests on the walls displaying symptoms of damp. The results of the test 3% and lower. The explanation given following these tests were “The available evidence and the CC tests would not indicate that the damp proof course has failed”.

When investigating the wall myself however, I noted that the drill samples taken from the wall were extremely small around 5 – 7mm. This would suggest that a very narrow drill bit was used to remove the sample and most likely with a high-speed drill.

It’s doesn’t take a genius to work out what will happen in this scenario.

I spent that afternoon reviewing the policy of the insurer with regards to re-inspections and sampling techniques. The Insurance re-inspection policy simply states, Procedures for this are clearly laid down in the PCA and BSI Codes of Practice, to which all member contractors work.” 

After looking through the PCA guidance, BRE guidance and instruction manual for the calcium carbide meter however, I still found no specific detail regarding drilling the samples i.e what size bit to use, what speed of rotation and what type drill to use?…

I have always used a sharp 12mm drill bit, on a slow speed percussion drill which means I have much less of a chance of damaging the samples taken. Also, if I’m taking multiple samples I have a several drill bits which I use in rotation. I have since found literature confirming my process.

Not convinced by the samples and results taken by others I decided to repeat the process using my technique. A 12mm sharp drill bit on a slow speed percussion drill. My results 7.2% taken directly below the other samples.

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It’s pretty obvious to state that if you take samples using a small drill bit at high speed i there is a significant risk that friction caused by the rotating drill bit will dry the sample as its taken. The result, a very inaccurate test.

Some could say this was undertaken intentionally to falsify a claim on behalf of the insurers, other could claim that the surveyor whom undertook the sampling was simply inexperienced. Either way, I suspect the opinion of the insurance company following my test results would have likely differed.

Anyhow, lets again take a look at these moisture content values. This 5% figure is often branded around as a guide to acceptable levels of moisture in masonry aided by that paragraph in the BRE document, however, the average moisture content of most uncontaminated dry building materials are often much lower than this figure.

Examples of standard moisture content values in modern masonry materials

  • Exposed (external leaf) brickwork and concrete upto 5%
  • Protected (internal leaf) brickwork often below 1%
  • Protected concrete 3%.

In reality we find that most uncontaminated and protected masonry materials will often have a moisture content value of less than 1%

There are however reasons why a considered dry wall could have an increased total moisture content in some cases above 5%. The BRE digest 245 confirms this “Experience has shown that some building materials possess a HMC (hygroscopic Moisture Content) of up to 5% even without the introduction of salts from external sources.“

This from my experience is true, although particularly relating to the moisture content of old stone walls where it’s not unusual to find the walls natural moisture content around 4 – 5%.

Old salt contaminated masonry may also provide elevated results through the hygroscopic uptake of airborne moisture.

The problem is a wall, isn’t just a wall. It’s made up of brick or block, mortar, backing plaster and skim. All materials which have completely different moisture tolerances.

The BRE Good Repair Guide 33 (Assessing moisture in building materials) includes a typical action chart based on the moisture content of building materials – see below

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As you can see the ‘damage likely’ action of the skim plaster is low around 4% Mc, similarly the ‘action required’ in render is around 5%. What this indicates is at these figures the potential of damage occurring to each material is high. If however, we compare these to the apparently acceptable tolerance of moisture within some masonry branded at 5% the two materials would be incompatible.

This I find is often the case and I suspect considering the era of this publication that the render percentages are based upon cementitious materials, it doesn’t state. Many modern light weight renders and plasters have a much lower tolerance to moisture than 4%.  

Considering the above, if we have a dry wall with a known moisture content of .5% which following repair the results during a re-inspection read 4.8%, this wall would still be considered dry by some. Yet a differential of 4.3% MC is apparent, enough in some cases to cause damage to the plaster.

So at what % do we consider moisture unacceptable? According to Google and Wikipedia“Structural dampness is the presence of unwanted moisture in the structure of a building” i would add to that with the potential of causing damage or decay to the structure of fabric of the building!

So the question is, when undertaking damp repairs are your contractors guaranteeing against rising damp, unacceptable levels of damp which may cause spoiling to plaster and decoration or simply salt contamination?……………………………………………………………….

I would like to say a responsible contractor should be protecting against all three however, clearly as we see time and time again this is not always the case!

Your thoughts and opinions on this are welcome.



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