Diagnosing Rising Damp

This article on rising damp was first published on ‘surveyingproperty.blogspot’ and later reproduced in a SAVA technical bulletin, (issue 17, 2014). Since it is my own material then I thought it was long overdue for inclusion on my own blog site. I have further supplemented and updated the information by the inclusion of a damp investigation flowchart that I developed for inclusion in a book I am writing. Please note that this flowchart is the copywrite material of the author and should not be reprinted or posted elsewhere without the authors permission. 

Deep wall probes in use
Deep wall probes in use

My own level of expertise regarding rising damp stems from two years research carried out into rising damp that resulted in a dissertation entitled, “The Efficacy of DPC Injection”. I have been actively involved in surveying damp properties and more importantly, teaching damp investigation for a number of years now and think there have been a number of significant developments over the last ten years to merit an update on current thinking, controversies and industry developments.

There have been a number of commentators who have done nothing to move this issue forward over the last few years. In particular Jeff Howell’s book, “The Rising Damp Myth”. Stephen Boniface, former Chair of the RICS Building Surveying Faculty, has also gone on record to state his belief that rising damp is a myth.

NB. It is worth noting that since this article was first published, Stephen Boniface has gone on record in stating that he has was misquoted on this issue. 

Whilst I understand the sentiment behind their extreme view, it is perhaps a backlash to a DPC industry that promotes rising damp as a common occurrence.

During my research into rising damp, I came across a PCA examination paper for their National Certificate in Remedial Treatment from 2005 where a question started with the statement that, “Rising damp is a common problem”. Of course we know it is not a common problem but it demonstrates the second of two extremes when a rather more moderate approach needs adopting. Both views cause a number of problems:

 The view that rising damp is a myth may cause building surveyors to form a view that it is not worth learning how to properly survey for rising damp.

 The supposition that rising damp is a common problem has led to a glut of poorly trained industry surveyors and widespread misdiagnosis due to over reliance on hand held electrical moisture meters.

Even the poorly trained have a real sense of security gained in the knowledge that, even if you misdiagnose, the waterproof renovating plasters applied internally will give the appearance of a dry wall, thereby leading clients to conclude that your diagnosis was correct. After carrying out a substantial literature review on this question I can with confidence state two facts:

1. Rising damp does exist and is a scientifically proven phenomenon.

2. Although it exists, it is incredibly rare.

The more common academic view is that between 5% and 10% of damp properties will be affected by rising damp; my own research puts the incidence at less than 5%. (Note that we are talking about a percentage of damp properties here and not total properties in the UK.)

So what exactly is rising damp?

The simple academic description would describe rising damp as “an upward capillary migration of water in
masonry”. You will find the reference to capillary action in most text books and it is in this area that most text books are long overdue an update. Bricks contain capillaries or microscopic tubes that are small enough to allow inter-molecular attractive forces between the liquid and solid surrounding surface; these forces allow a liquid to flow in narrow spaces against gravity. The problem here is that we now know that rising damp has two moisture transfer mechanisms, i.e. capillary action and diffusion.

It is generally thought that molecular diffusion (Fickian) is the moisture transport mechanism for water molecules moving through cement paste. Some of you may remember this from your school physics lessons but in simple terms diffusion is the spreading of solutes from regions of highest to regions of lower concentrations caused by the concentration gradient. It is the same for concrete floor slabs; water moves up through the floor slab by a process of diffusion and not capillary action.

A new definition for rising damp

It is time to propose a new definition for rising damp and I would suggest the following description:

“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.”

Maybe not as snappy as the original definition but it clears up a number of issues and in itself can be used as an aid to diagnosis and specification.

Since we know that the mortar joints are primarily affected then it serves very little purpose in drilling and injecting brickwork without also treating the mortar joints. We need to qualify this statement because we have something of an anomaly when it comes to discussing the mortar joints.

Tests were carried out at South Bank University a number of years back which failed to replicate rising damp in laboratory conditions. The tests were bound to fail because account was not taken for the fact that a new DPC mortar bed is impermeable to moisture. However, after 30-50 years of environmental exposure the mortar degrades and rather than providing an impermeable barrier, it then becomes the main moisture pathway.

For reasons of practicality and aesthetics we should have completely moved away from injecting brickwork and retrofit DPC injection should focus on the mortar bed and perp joints. However, we are getting ahead of ourselves because we’ve not yet discussed correct diagnosis.

It makes no sense whatsoever to install a retrofit chemical injection to a property that already has a physical DPC installed unless you can evidence failure of the existing DPC; to my knowledge, no one has yet done this.

Diagnosing rising damp

There is a view within the damp proofing industry that rising damp can be diagnosed with nothing more than a hand held electrical conductance meter and a great deal of experience. There is not a shred of scientific evidence to support this view and in fact it is well documented that hand held electrical moisture meters are of limited use due to the fact that they are calibrated for timber and not masonry. They are also prone to giving false positive readings for damp wherever they encounter salts, carbonaceous materials or backing papers such as foil damp.

You need to confirm that three conditions are present to definitively confirm a case of rising damp:

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 1.5 m.

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 have 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.

NB. I have since discussed and debunked the academic requirement for salts analysis in a later article entitled, ‘Rising Damp: An update for 2015.’

Unless you can confirm each of these three conditions then, your diagnosis is based on guesswork. On the upside, due to the use of waterproof renovating plasters no one will ever know you got it wrong. It is a fact that the application of renovating plaster provides the perfect cover up for bad surveying practice.

The following flowchart illustrates the damp investigation process that we teach on our damp investigation training course.

Damp Investigation Process Flowchart
Damp Investigation Process Flowchart

Do physical DPCs fail?

This was a key question asked in my research and I could not find a shred of evidence to support the view that physical DPCs fail though I accept that not enough research has been done in this area.

I did note that cracked slate DPCs had been found but as one of my contemporaries wisely pointed out: “A crack is a crack and a capillary is a capillary”, you will hopefully see the logic in this statement.

Slate DPC still fully functional in a building that is circa 140 years old.
Slate DPC still fully functional in a building that is circa 140 years old.

What is clear is that DPCs are regularly found to be bridged or compromised in some other way.

How has the damp proofing industry changed in the last ten years?
It is fair to say that the process of retrofit DPC injection has been taken out of specialist hands over the last ten years. In the past, expensive equipment and specialist training was required for injecting siliconate and stearate fluids into brickwork. These are still used, but the market has moved more towards the use of aqueous silane creams injected into mortar bed and perp joints.

The process is so simple that anyone with a reasonable degree of DIY skill can successfully carry out chemical injection. All that is needed is a hammer drill, a tube of your chosen water repellant cream and an application gun.

The cream is applied into 12 mm holes drilled at 120 mm intervals which will then diffuse into the wall via the mortar course to form a damp course to BS 6576. The drillings are simply made good with re-pointing rather than being sealed with plastic plugs, as used to be the case. Moreover, aqueous silane creams are far safer to use than the old types of injection fluids and come with far less chance of user error; anyone who ever used these fluids will tell you how they burned in contact with the skin.

It was not unusual for pressure injected fluids to be injected into voids within the brick and in any event these fluids were never designed to give full penetration that forms a continuous barrier to damp.

They worked by a process called viscous fingering which in basic terms means that you have fingers of waterproofing within the individual masonry unit rather than a complete barrier.

The best you could hope for was that you stop a fraction of water rising in the wall and restore moisture equilibrium. Moisture equilibrium is achieved when water is evaporating off the wall as fast as the damp is rising; thereby controlling any further rise in height of the damp. Silane creams are designed to give a complete impervious barrier to damp and on that basis alone outperform the old liquid systems.

Retrofit DPC injection has always been a two part management solution with the internal re-plastering being as, if not more important, than the injection work. Plaster becomes defective when chronic damp dissolves the calcium sulphate within the plaster, which make it extremely porous but salt contamination is the primary reason to hack off and replace the plaster. These salt contaminants are hygroscopic and will continue to absorb moisture from the atmosphere causing the wall to remain damp.

In the early days it was common for plaster to be hacked off and replaced with sand and cement render containing a waterproof additive that was then finished with a coat of Carlite finish. These days waterproof renders are rarely used with most contractors and specifiers opting for one in a range of waterproof renovating plasters that have become available.

For the record, I am neither anti damp proofing industry nor anti retrofit injection; I simply believe that the vast majority of damp buildings can be cured at source using nothing more than minor building works and the damp proofing industry would be best served by accounting for this fact.

I have both specified retrofit DPC injection and used it personally because pragmatically occasions do arise when you can do little else. What if a neighbour’s yard has higher ground levels than yours and is draining against you gable wall? It is unlikely that lowering your neighbour’s ground levels will be an option. A truly independent and competent damp surveyor will not hold with extremist views that rising damp is a myth but will also understand that rising damp is incredibly rare. It is this reasoned and pragmatic approach that will leave them best placed to appropriately specify works to achieve a cure or a management solution. Wherever possible, a cure should always be the preferred option and retrofit DPC injection falls firmly under the heading of management solution.

7 responses to “Diagnosing Rising Damp”

  1. Michael Kelly avatar
    Michael Kelly

    Are the PCA internal vapour permeable plasters a suitable cheaper alternative to traditional lime plaster? For example for a Victorian mid terrace after resolving damp ingress issues.

    1. Joe Malone avatar
      Joe Malone

      Hi Michael,

      One of the biggest lies told by damp proofing industry, is with regards to the vapour permeability of their finishing plasters. If, they are sold as part of a damp proofing treatment, then they are tanking plasters, and as such considerably less vapour permeable than a standard bond and skim, or lime plaster. Limelite, is often used, because with ‘lime’ in the name, surely it must be good? Well actually no, it’s still a cement based tanking system. Granted, it may be more permeable than a cement render tanking system, but it is still a tanking system.

      Lime is lime, and as soon as Portland cement is added, is ceases to function as a breathable lime plaster, used for conservation work. Almost everything is vapour permeable, even glass, is on the permeability index scale, but I’d not try and sell that as a breathable product.

      There is a more critical question… Is your aim to cure the problem, or to hide it by installing a management solution? Damp proofers sell management solutions, designed to hide the damp behind waterproof tanking systems. These systems do a great deal of damage in the medium to long term, and we never recommend them, and never specify them. I think that Chartered Surveyors have a responsibility to properly diagnose dampness, with a primary aim of curing the problem; this is core building pathology, and should never be outsourced to anyone, whose primary aim is to sell a damp proofing management system. I’m generally not interested in the merits of damp proofing systems, or whether they work in managing dampness, pragmatically, we see properties damaged time and again by these systems, and believe they should be avoided. Focus on diagnosing the root cause of damp, and removing that root cause. Specialist damp proofing systems are rarely, if ever needed.

  2. Jeremy Carpenter MRICS avatar
    Jeremy Carpenter MRICS

    Is the below product no good ?

    Sovereign Renderlite Renovating Plaster is ideal for any plastering situation. Its performance characteristics, which allow walls to breathe but prevent the movement of liquid moisture and salts, make it particularly suitable for use on damp walls or after the insertion of a chemical DPC.

    1. Joe Malone avatar
      Joe Malone

      Hi Jeremy,

      If you want to install a management solution, DPC injection, and associated waterproof plastering (tanking), then I’m sure it’s fine. However, these products are now being sold as breathable tanking systems, and the whole premise is nonsense. Everything is breathable, to a greater of lesser degree, so in this case “breathable” is a relative term. Tanking plasters reduce breathability, and therefore moisture evaporation, and cause induced rising damp. Please type in ‘induced rising damp’ into the search bar if you want to understand this phenomenon. I’m of the opinion that as Chartered professionals, we should be advising clients on what is needed to cure, rather than ‘manage’ dampness in properties. We never specify management solutions, as they are rarely, if ever, needed.



  3. Daniel avatar

    Hi Jo,

    Me again, i am wondering how you confirm the presence of plaster contaminated with hygroscopic salts? Is the solution here to always hack off and replace with a lime plaster?

    ….Where do the salts come from?


  4. terry avatar

    found your blog very interesting and a useful balanced view – I recently reviewed articles on rising damp, damp meters and treatments and was somewhat surprised at the extreme range of views on the subject, from RICS surveyors with typically heritage focus condemning and denying the existing of rising damp and the value in any form of injection system, to those recognised companies in the damp industry glibly promoting injection systems and their promoted plasters as the saviour of damp and associated dry rot issues with the words “guaranteed” plastered (forgive the pun) everywhere. Where is best to look as a RICS surveyor myself looking to advise my clients factually on the issue of damp particularly in renovations to period properties, and do you have insight into how the range of views across the industry and particularly in RICS is likely to be resolved into a common agreed factually based position on the subject? thanks

    1. Joe Malone avatar
      Joe Malone

      Hi Terry,

      Thanks for your comments. I’ve been giving talks at RICS events for a number of years now, on damp, and other building pathology related issues. To my mind, it’s simple, RICS have to simply adopt a regularised standard for the approach to surveying for dampness, and they further have to understand the simple difference between a cure and a management solution. Damp proofers are not interested in cures, they’re interested in selling management solutions that hide the damp. The whole argument as to whether or not rising damp exists is an unnecessary distraction, but the science was in a long time ago, and of course damp can rise up walls. Whether it’s ‘true’ rising damp in the academic sense, is another discussion, but Chartered Surveyors need an understanding of a common investigation process, to first allow then to understand whether moisture is present at depth in the masonry, and to further understand what the moisture profiles tell them.

      Here’s the problem for RIC’s… While the people who book their CPD events are very nice people to deal with, they are not technical people, and are often under pressure to book a speaker, without understanding that speakers approach, or view of the technical issue to be discussed. I myself was recently booked for a talk on building defects, only to find that the speaker booked for the damp talk, provided views that were contrary to my own, and conflicted with information I was providing at the same event.This particular speaker worked in the damp proofing industry and of course was advising the audience on the benefits of retrofit DPC injection, whilst I am of the firm opinion that this is core building pathology, and Chartered Surveyors should be directing their clients towards curing the problem.

      I’m told by my RICs event contacts that over the years they have been receiving poor audience feedback on speakers whose sole aim is to promote and sell their products, because of course, the audience see straight through that, and pay a lot of money to attend these events, so they expect value for money and to come away, having actually learned something that will benefit them in the field. The reality is that there are actually very few real experts in damp, and this makes it very difficult to book speakers who are not actually damp industry salesmen. Perhaps the way around this is to be clear on whether speakers are covering cures or management solutions on damp. I have no problem with the latter, so long as clients know they are making an informed decision to buy into a management solution, and the risks that come with such a system, of which there are many. However, the primary aim of any Chartered professional should be directed towards curing the problem, and that needs a full understanding of the investigation process, to aid diagnosis of the underlying cause.

      Kind Regards. Joe Malone

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