Guest
Article - Joe Malone - Principal: Malone Associates Ltd
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.
Following on from my articles 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.
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.
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Figure 1. Protimeter
salts analysis kit. Source:
surveyexpress.co.uk
|
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 only give a positive test result when
Nitrates levels are above and below 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.
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Figure 2. Colour
card familiar to freshwater fish keepers. Source: www.cichlid-forum.com
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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.
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Figure 3. A positive
nitrates test using Protimeter kit with Palintest tablets
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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.’
Before 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.
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Figure 4.
Alternative Nitrates Test Kit Source: Authors own
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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.’
In figure 5 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.
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Figure 5. Positive
nitrates test result in tap water. Source: Authors Own
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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.
Joe Malone - Principal: Malone
Associates Ltd
First Published: 16/2/15 at www.buildingdefectanalysis.co.uk
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