'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 1.5m.
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A Negative salts analysis in a property diagnosed as
having rising damp.
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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.
Unless you can confirm each of these three conditions then to be frank, 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.
Do physical DPC's fail?
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Presence of a functional physical DPC has not affected the retrofit
www.buildingpathology.
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This was a key question asked in my research and I could not find a shred of evidence to support the view that physical DPC's fail though I accept that not enough research has been done in this area. I did note that cracked slate DPC's had been found but as one of my contemporaries wisely pointed out, 'A crack is a crack and a capillary is a capillary', you'll hopefully see the logic in this statement. What is clear is that DPC's are regularly found to be bridged or compromised in some other way. 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.
How has the Damp proofing industry changed in the last ten years?
It’s fair to say that 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 12mm 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.
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| If it’s installed above the timber floor joists then what good is it doing? This property had two courses of blue engineering bricks as dpc. |
It wasn’t 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 in was common for plaster to be hacked off and replaced with sand & 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 or 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 him/her 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.
Joe Malone BSc (Hons) ICIOB - Head of Asset Management - ALMO Business Centre Leeds
The writer of this article is an advocate of paid independent damp surveys and in no way endorses any damp proofing advertisement (PCA affiliated or otherwise) linked to this article.
Information/opinions posted on this site are the personal views of the author and should not be relied upon by any person or any third party without first seeking further professional advice. Also, please scroll down and read the copyright notice at the end of the blog.
Following on from my recent comment on Part One of this article I would just like to say that I find what you say to be very helpful and balanced and this makes for an interesting read. It adds to the debate on how to diagnose and deal with damp problems.
ReplyDeleteWhat I would like to see however is more analysis and consideration of different building types and eras.
There seems to be a general acceptance that any masonry structure will be the same. What you say is perhaps valid for modern masonry walls built using cement mortar and perhaps even for the solid masonry walls (9-inch brickwork) from the late Victorian and Edwardian period. However, when looking at masonry walls built in lime mortars (and here there can be a wide variety of limes) we have to remember that some are 9-inches thick, but others are thicker and some are thinner. Some bricks were baked hard and some very soft. Not all brick walls are the same simply because they are of brick. Some walls were always covered with a finish such as a lime render and some were not. The further back in time we go the far greater the variety of construction and materials and finishes that could all influence the issue of damp.
My view is that we cannot simply diagnose and deal with all of these varied structures in the same way because they fundamentally function differently.
For the past 20 years or so I have been advising clients to get buildings to breath and function as originally intended (i.e. no retrofit treatments) and to my knowledge have not yet had anyone come back to me with a continuing problem.
I totally agree that a surveyor must take a reasoned and pragmatic view and should be open to all possibilities as to what damp exists, why it is there and how it might be dealt with. This does include taking careful account of the very nature of the structure being dealt with.
The articles in Parts 1 and 2 are very interesting and a helpful contribution to this matter.
Stephen Boniface
Hello Stephen,
ReplyDeleteFirstly please accept my apologies if I have misquoted you but your subsequent comments in response to this thread led me to believe that I did actually understand your motivation on the quotation made and I completely understand your reasoning.
You have made some very interesting comments with regard to historic buildings which I find very interesting and which I am also in complete agreement with. When I teach students the fundamentals of damp investigation I ask them to distinguish between buildings that manage moisture via the raincoat or overcoat principle. So old historic buildings built with lime mortars, lime plasters etc operate under the overcoat principle and are actually meant to absorb some moisture and go through seasonal wet/dry cycles. A key question I asked in my research on rising damp is whether DPC injection was appropriate for use on historic buildings? I've cut and pasted the text from that part of the literature review and in fact you'll note that you have been directly quoted.
It’s clear that published data recognises different damp proofing requirements for old and modern buildings. Thomas A R, Williams G & Ashurst N (1992, p.3) explain that before the public health act of 1875 it was not compulsory to provide the walls of a building with damp proof courses. Most old buildings lack these and therefore damp will rise in the walls to some degree. The best solution may well be to take measures to help the building ‘breathe’. It may be preferable to encourage the moisture to evaporate quickly and easily, rather than try to restrain the damp. Repointing or replacing a dense render with a lime mortar will often improve a damp wall and enable rising damp to dry out. The converse is also true. Repointing or re-rendering walls, particularly plinths with a cement rich mortar, is likely to create or exacerbate damp problems.
The approach taken to prevent damp in modern buildings (positive exclusion by thin barriers, etc) is fundamentally different to older buildings (moisture management - breathability) and the remedial works appropriate for one technology are totally incompatible with the other. Therefore surveyors trained to deal only with modern buildings do not have the appropriate understanding/Knowledge to deal with older buildings. Boniface S (2005)
ReplyDeleteBreathability is a key issue for historic buildings but not one that’s recognised by chemical dpc ‘specialists’. The significance of wall coverings in relation to breathability is best highlighted by Torres M and DeFreitas VP (2003, p. 4) who used computer modelling techniques to analyse the distribution of water content over the cross section along the height of the wall for one year. Each wall had a different surface finish and our results showed that the naked wall is the better solution. We confirmed that naked walls were those with lower rise heights and lower water content, followed in increasing order by walls with interior Gypsum plaster, walls with cement plaster, walls with tiles up to 600mm and walls fully tiled. As far as we can make out, the evaporation is more difficult with a covering so the rise height grows until a new equilibrium between the water that comes in by capillarity and the water that goes out by evaporation is reached.
The point regarding impermeable wall coverings is picked up by Ashurst J&N (1998, p.28), referring to dpc injection work the author states that the treatment includes replastering with a strong impermeable, sand and cement render. By any standards, this is an inappropriate measure for older properties built with (permeable) lime mortar, and will interfere with the subsequent diagnosis and treatment of any genuine dampness problem which may exist.
Thomas A R, Williams G, Ashurst N (1992, p. 8) concur with Ashurst and explain that a common way of coping with rising damp is to strip the internal plaster, and replace it with a water-proof render up to and well above the tide mark. This tends to force the water further up the walls, and usually recreates the same problems at a higher level. This method is not recommended.
Please also note my recommendations with respect to this particular problem...
There are significant errors of omission in both BS6576:2005 and the PCA code of practice. Both standards do not recognise the specific requirements relating to the management and control of damp in historic buildings, particularly the fact that historic buildings are designed to ‘breathe’ by the use of permeable building materials used during their construction. This has engendered a ‘one size fits all’ approach by the dpc industry and they are not tailoring their approach to historic buildings. Both BS6576:2005 and the PCA code of practice needs updating to reflect these facts.
Finally let me close by thanking you for your balanced, informative and constructive comments
Joe Malone
i like this post, thanks
ReplyDeleteJoe
ReplyDeleteThanks for the articles, they're very interesting and I agree with your views.
The reason why people get confused about rising damp is because the term rising damp is confusing and could refer to a specific type of dampness or a general term for any base of wall dampness. It depends who's using it.
I have never used this term ever in any survey I've ever written. One reason is because I seldom if ever see it ( I inspected over 900 properties in 2012) but more importantly the client will think it means any old moisture rising up a wall.
I've come to the view that Rising Damp should be called Rising Salts. If you use the term Rising Damp it could be misunderstood for any old dampness rising up a wall such as a pipe leak, high ground levels and the like.
No, Rising Damp is less about dampness and everything about salts as you have stated above!! Use the term Rising Damp and I don't actually know whether you mean nitrate rich moisture from the ground rising up the wall or tap water rising up the wall from a leaking lead water main under the hall floor.
Anyway this topic is slightly academic because if the dampness is coming from the ground, my next question is why is the ground damp, it shouldn't be damp if the building was designed, built and is maintained correctly.
Please note that you will only have the same view as me if you have actually built a building or think like a builder. Buildings were built to be dry and if they have become wet some element of the building has either malfunctioned or been altered.
All the best
Hi,
ReplyDeleteWe can get into some very interesting debate about the specifics of true rising damp versus wall base damp and it can and does get very confusing. It is the reason why salts analysis becomes such an important part of the diagnostic process. The damp proofing industry prefer to believe that rising damp moisture profiles are good enough in themselves to aid diagnosis but of course the sources of moisture contributing to wall base damp can be attributed to a host of factors. The primary response should always be to identify and eliminate the source of moisture.
True rising damp is as a result of moisture being leached up the wall from below ground level, this moisture will contain nitrates from the soil. For anything other than true rising damp then I always refer to it simply as wall base damp to give a clear distinction between the potential causes and the potential cure or management solution. You're right of course in stating that Buildings are built to be dry but I would further qualify this by saying that buildings are built to be dry internally. As previously stated some older building fabric is built on the overcoat principle and as such is meant to go through seasonal wet/dry cycles. Adequate wall base ventilation is especially critical for these properties.
Kind Regards. Joe Malone
Just a short comment: I know for a fact that many (not all) builders and contractors see the damp course, both the brickwork and the tie in with the DPM, as a pain in the neck and something that needs to be rushed to completion so that the bricklayers can "get on" I have hardly ever seen an instalation carried out correctly, especially at the internal corners where there is often a messy void with damaged and stretched membrane material folded into lumps with the Bwk.DPC on top. Building inspectors never appear pick up on it so it's down to the installer and the supervisor. Even with pro installation the membranes are then often then worked over and damaged by falling objects too.
ReplyDeleteI once worked in Geo Membranes BTW.