Rising Damp: An Update for 2015

Rising Damp: A Salty Problem

A positive test for Nitrates using the Protimeter salts analysis kit but is it fit for purpose?

A positive test for Nitrates using the Protimeter salts analysis kit but is it fit for purpose?

Following on from my articles on rising damp written in 2013 I thought it was time to provide a further update on one problem in particular relating to the diagnosis of rising damp. In my update for 2013 I wrote that, ‘you need to confirm that three conditions are present to definitively confirm a case of rising damp.’ These are:

1. You must have a rising damp moisture profile. That is a profile that is wetter at the wall base but gradually decreases with height to a theoretical maximum height of circa 1.5m.

2. You must prove that moisture is present at depth in the masonry and it is not enough to take surface readings from the plasterwork. You will need deep wall probes or a calcium carbide (speedy) meter to confirm this on site.

3. You will need to confirm that nitrates are present in the damp apex of your moisture profile. This will involve doing on site analysis or sending a sample off to the labs. You might have noted that I’ve ignored chloride salts because these can be present in tap water or building materials. A positive test for nitrates confirms that the moisture has leached up from the soil.

The Academic Description for Rising Damp is Wrong!

My academic research into rising damp led me to the conclusion that most text books are wrong in their description of rising damp since they state that it is caused by capillary action. Since we know that the major moisture pathway for rising damp is the mortar perps and since we also know that the moisture transfer mechanism in mortar is diffusion then clearly the generally accepted cause by capillary action is incorrect. It is probably worth reprinting my own updated description at this point…

‘Rising damp is an upward migration of groundwater in masonry walls. It will act in combination on the masonry units and their separating mortar joints or it will act primarily on the mortar joints. The moisture transfer mechanism in masonry is capillary action whilst the moisture transfer mechanism within mortar is diffusion. The major moisture pathway for rising damp is the mortar perps so it can be stated that there are dual moisture transfer mechanisms for rising damp, diffusion and capillary action’

The purpose of this article is to right another wrong with regard to the academically accepted principle for salts analysis. If you note again the requirement to prove the third condition, the need to prove that Nitrates are present in the damp apex of your moisture profile. This requirement stems from the fact that Nitrates are present in the soil so if moisture is leached up from the soil then it stands to reason that the moisture contains Nitrates. Personally I have always used the chloride test very little since it has extremely limited value in the course of most damp investigations and it is a test that has always been of zero value for the diagnosis of rising damp, simply because we know that chlorides are present in tap water so a positive test for chlorides does not help us determine the source of moisture.

The Nitrates Anomaly

When testing for Nitrates we do so on the assumption that Nitrates are not present in tap water and therefore a positive result moves us to conclude that moisture in the masonry has been drawn from the ground. I’m only aware of one salts analysis kit sold by Protimeter and indeed this is the one I use. Interestingly, Protimeter do not make their own salts analysis tablets and these are sourced from a company called Palintest. However, we know that Nitrates can be present at very low levels. World Health Organisation guidelines stipulate a guideline for 50mg/l or less. So this raises a key question… Do we know that the tablets supplied by Palintest for the Protimeter salts analysis kit are discriminatory enough to give a positive test result only when Nitrates levels are above 50 milligrams per litre? If not, then the source of moisture cannot be determined using this test since a positive result may also be obtained when the source of the wall base damp is a leaking incoming water main containing Nitrates at low levels of 50mg/l or less? If you have used the Protimeter kit you will know that a positive test for Nitrates turns the water cherry red and there is no colour chart to match against your sample to help determine the approximate quantity of Nitrates present. The practice of matching the sample colour obtained against a colour chart is a principle that may be familiar to a lot of freshwater fish enthusiasts since they have to regularly check Nitrate levels in their fish tanks to ensure levels do not become so high as to become dangerous for their fish

Colour chart to determine nitrates level

Colour chart to determine nitrates level

The Protimeter test for Nitrates appears to be less discriminatory than the test used by freshwater fish enthusiasts since it will turn cherry red and give a simple positive result with no clue as to the level of Nitrates present.
I was uncomfortable with this and decided to contact the technical team at Palintest to ask them how discriminatory the Nitrates test was?
They were incredibly helpful in providing the following response…

‘Your question is a good one. I’m afraid you won’t ever be able to be certain that the nitrates don’t come from the tap water. The test doesn’t know the source of the water, it’ll just react to any nitrates present.

You’re also correct that the limit for nitrates is 50mg/l.

What I would recommend is to test the tap water on the site to test the ‘baseline’ nitrate level. If your ‘real test’ is higher than this, you can be sure that some nitrate is coming from the rising damp. If it’s less or equal to the baseline though, you aren’t going to be able to tell.

You could expand your test protocol to include other minerals (sulphate, chloride etc) which would be able to give you some more confidence that the water is from the ground as opposed to the tap but you would need more equipment and would be a bit more complex than your current method.’

Screen Shot 2015-09-20 at 09.58.06Before I even asked the question of Palintest I was already experimenting with a Nitrates test kit manufactured by Salifert. I chose this particular kit since I’d read on most forums that this was generally thought to be the most accurate kit. The kit is supplied with a colour match chart and is significantly cheaper than the Protimeter test kit. In fact I had been doing precisely what was recommended by Palintest… I was and am testing the tap water to establish a baseline Nitrates level according to my Salifert colour chart before I take a sample from the wall. The advice given by Palintest is good but of course ignores the issue relating to the absence of a colour chart in the Protimeter kit. It would seem that I was being advised to use another kit since the Protimeter kit can not discriminate and will simply, ‘just react to Nitrates present.’


Nitrates Test result of 25mg/l

Nitrates Test result of 25mg/l

In this image you can see where I have obtained a positive test result for Nitrates at a level of around 25mg/l but this was for a tap water sample.

My trials and research with this alternative test method are still ongoing since rising damp is incredibly rare and to date I have only obtained negative results from walls and positive results from tap water. I will need substantially more time to evaluate the effectiveness of my alternative Nitrates test but what is clear is that an alternative test is needed or some refinement is needed in the Nitrates test kit currently used by most building surveyors or damp investigators.

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  • Excellent article, and it does pose some issues for any of us surveyors who happen to do defects analysis. I rarely do this, concentrating on building surveys, which of course are only a snapshot of the condition of a property. I am not sure that I have ever come across an instance of true ‘rising damp’. Plenty of penetrating damp, and one house last week that appeared to have damp to the walls, but more likely due to a previous water leak from above, that was trapped by the dpm. The client of course though of ‘rising damp’.
    A client should always seek the advice of an unbiased professional, and damp often takes some time to diagnose, and as I advise clients, sometimes a small level of damp may need to be tolerated. It depends on the severity, and the effects. There can be something of a public hysteria about ‘rising damp’.
    I have a defects analysis visit shortly for damp, and I am wary that there is going to be an easy diagnosis or solution.

  • As an independent surveyor working in the field of damp and timber infestation I find your article quite insightful however, from my perspective, I am usually looking to determine whether plaster is contaminated with hygroscopic salts; I find salt tablets very useful in helping me advise my clients whether there is a need for re-plastering . Clearly I am also looking to determine the cause of dampness and, have to say, in my experience, that an original damp proof course ‘fails’ due it’s negation rather than abject failure.

    • Joe Malone

      Hi John,

      I prefer to say that DPC’s are compromised as as opposed to describing them as failed, and I’ve yet to see any evidence whatsoever that physical DPC’s fail. I’m of the opinion that issues with hygroscopic salts are over stated. If the plaster is sound then we simply advise brushing those salts away and would never advocate replacing sound plaster purely because of salts.

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