'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. |
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. |
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.
