Don’t be a drip! Watch out for dodgy damp advice

I, among others, have listed links to Heritage Scotland and SPAB publications that deal with damp. I think, as a non-expert, that they seem to give a good introduction to damp causes in old buildings. They allow people with a damp problem to consider possible causes and remedies and have a more informed discussion with any “expert” they might ask for advice. However, rising damp is referred to, so presumably you accept this can occur (even if generally only in the lower 300mm of a wall for example)?
The maintenance of breathability of structures and surfaces is a point well made throughout this conversation, and chemical treatments or materials that destroy this are to be deprecated. No doubt many reading these posts will take this on board.
It would be useful if Which? could extract the facts from this conversation and produce a summary of what people with damp problems should know and do, and what they should avoid. I wonder if that would excite more controversy?

Malcolm

This seems to be in danger of turning into a flame war between Heritage House and Dry Rot, something I don’t think is particularly appropriate for this kind of forum.

I agree with you that the publications of HS and SPAB are a good starting point. The former is a government department with more than a passing knowledge of historic structures, including the care of their own estate. We have provided links to their advice and I would very much encourage readers to work their way through such publications before coming to any firm views on the ways of dealing with dampness.

As for rising damp, I do not personally doubt that it exists in both theoretical terms (the Edinburgh paper on the physics of capillary movement, for example) and practical terms. What I would dispute is the presumption that it is endemic to anything like the extent proposed by damp proofing “specialists” or that an injected dpc is necessarily the correct way of dealing with it.

In my experience, many cases of “rising damp” are in fact due to misdiagnosis of penetrating dampness (especially on lime mortared stonemasonry buildings) or have been exacerbated by poor management. I used to smile when I saw someone trying to inject a chemical dpc into a whinstone wall instead of improving the ground drainage, but now I just despair.

The other thing which perplexes me is the public perception that PCA members are seen as the automatic experts in contrast to, say, independent building surveyors (note: I am not an RICS member) or other professions. And yet we hear here stories of differing diagnoses, multiple rounds of failed treatment, and so on.

It’s enough to make you cry!

Roberto

Upon reading your post, I turned and picked a slightly dog-eared copy of Massari off the shelf. The Rome 1993 edition, for what it’s worth, which according to the receipt inside cost me £24.50 from Archetype in Fitroy Square back in 1998.

There were markers at two locations:

Page 88, beginning with “capillary interception with resins” (that’s an injected dpc, for any homeowners till reading) moving on to trenches (only if the dampness is due to surface water management) and “worthless pseuodscientific methods”. I especially like the section on Electro-osmosis.

Page 177, “Cooling, not water penetration”, or in other words “check for condensation and dew point”.

I must admit that I don’t agree that all of Massari’swork is relevant to other parts (predominantly northern) of Europe and consideration has to be given to construction techniques. But yes, I read it years ago and would concurr that anyone working in the field should have made themselves familiar with it.

Robusto

There’s a reason that we used to use slate DPC in mass masonry construction, at least in areas where we used more porous sandstones (there is obviously little point in granite/whin/greywacke areas), and even if building a new mass stone wall today I would look at incorporating some sort of physical barrier.

I’m always cycnical about the relevance of these very large southern European walls with the salt “tide mark” 1.5m up the outsidfe inasmuch as they are so very different from the kind of constructions we see in most of northern Europe and certainly the UK. Indeed the four key issues in determining the scope of rising damp, where it exists, seem to me to be:

1. Thickness of wall.

2. Construction of wall, i.e. porosity of both the stone and the mortar matrix.

3. Amount of water in the surrounding ground surfaces.

4. Evaporation / Microclimatic issues.

In my personal experience, and I have to say as I was always taught at university, rising damp is rarely (if ever) seen more than 300mm above highest external ground level on a traditional mass masonry wall 450-600mm thick in this country. The highest extent tended to be where the core was an open/rubble/mortar mix – the “sponge” effect, ground water levels were high, and where surrounding surfaces could exacerbate wetting through splashback.

Under those circumstances I have always:

a. Ensured that penetrating dampness on the faces was controlled through a robust programme of hydraulic lime repointing, including core voids, the hydraulicity determined to suit local conditions.

b. Improved ground and surface water drainage at the immediate foot of the wall in order to ensure that water is not tending to pool around the footings, including cutting-back metalled pathways and pavements. I should add that, although a believer in French drains, care has to be taken to ensure an inadvertent reservoir is not created in heavy clay soils.

c. Where a new solid floor is being cast in, turning the DPM up the inner face of the wall 450mm above ground level in order to limit the scope for transference to internal linings. That said, I often use either lath & plaster on studs (for historic work) or gypliner (modern work) rather than plastering on the hard.

Problems I have seen on other projects where injected dpcs are used include the inevitable concentration of salts and dampness within the lower section of the masonry leading to accelerated weathering and spalling of natural stone or softer brick faces.

I should also say that, where I work, lime harls (i.e. hand cast renders) can help in increasing avaporation from the external faces and thus controling rising AND penetrating dampness in a subtle but important way. This does, however, tend to be restricted to historic properties.

As a final shot, I’ve always been a little worried by those who advocate limecrete slabs being laid directly onto hardcore without a DPC on the basis of breathability. This is, of course, only really an issue in the conservation & repair of “properly” historic structures however it seems to me that it only works until you put a moderately impervious tile or floor finish above, at which point the game is a bogey. I wouln’t recommend it.

In summary: it’s very complex and independent, impartial advice is usually a good thing. But said advice has to come from people who have studied and understand the issues.

Give me some links to technical and/or academic papers and I’ll happily read them, as long as they’re not in Dutch!

Presumably poor soil conditions in the Netherlands would tend to countenance against creating slip planes using dpcs, but I’d be intrigued as to how they control dampness.

It would be interesting to know which northern european countries use dpcs, and which don’t. Other than Holland, which has been cited before, do you know of others?

Bule

Your suggestion is correct: find the source of the pentrating dampness. Treat the cause, not the symptom. The Historic Scotland guides I linked to earlier would be a useful starting point.