Rising damp diagnosis

Rising damp misdiagnosis costs the UK economy £500 Million every year.

Yet there has been no clear, consistent and empirical method of determining rising damp.

It is our opinion that rising damp exits, but is rare and wildly overstated, mainly through:

  • conflicts of interest and
  • insufficient investigation.

As independent damp surveyors, we have no financial or professional interest in whether or not rising damp is common or rare. We work in London where groundwater is pumped out, so the risk of rising damp is low.

However, as we often deal with clients upset with a damp proofing contractor’s diagnosis pr work. So we have developed a simple method for eliminating rising damp – see end of this post.

Why doubt Rising Damp?

  1. It is easy to demonstrate that water rises up porous material by putting a brick, porous tile or kitchen paper in water. Water from any source will rise.
  2. The rise is about 10 times greater when there is a boundary below, stopping water from descending through gravity and dispersing such a physical barrier like a damp proof course (“DPC”), or in the case of rising damp, the water-table – try it yourself.
  3. Dampness at the base of a wall will appear to rise, as volume of water increases, like water poured into a bath.
  4. All sources of water appear to rise with increased volume, when in contact with the base of a wall:
    • mains-water leak,
    • rainwater,
    • condensation.
  5. A leak, rainwater and condensation will only stop when the source is fixed.
  6. Rising damp treatment may hide or displace a leak, rainwater or condensation, but it won’t stop is.
Water rises. Note plaster reduces evaporation, with minimal effect on height.
This demonstrates the rise is from above the boundary or water-table, in this case water in the glass vessels.
Unbounded water mainly descends – try it.

What is rising damp?

Water rises whatever its source. 
However, the only source of water that can’t easily be treated at source and is bounded, and therefore causes the greatest rise, is groundwater. For that reason, Rising Damp is defined as:

Rising damp is the rise of groundwater in masonry.

Groundwater is the water under the water-table.
Groundwater in London showing extraction.
Source British Geographical Survey

Why does rising damp need treatment?

Unlike condensation, mains-water leaks or rainwater in soil, groundwater cannot be easily be drained away. It is often more economic to create a barrier to stop groundwater from rising through masonry. In Victorian times a sacrificial trench with drainage was often built. From about 1875, slate or bitumen Damp Proof Courses (“DPC”) became common place.

The breakdown or lack of a DPC is often sited as a reason for rising damp, without evidence (evidence of the break in a DPC, how much water can rise through a broken DPC and whether or not DPCs are beneficial, is another subject).

Chemical damp proof courses are the modern go to solution to protect a property against groundwater.

failed damp proofing
Example of chemical damp proofing after two attempts by London’s largest damp proofer.

Chemical DPCs

Thixotropic creams such as silane/siloxane (e.g. DryZone by Safeguard) are effective at reducing the absorption of water in bricks and mortar – try it for yourself. We will often recommend running a 10mm beed of DryZone cream along the base of the wall to reduce the absorption of moisture forming on a solid floor.

We would only recommend injecting chemicals if the source of dampness was groundwater (i.e. rising damp), which we have yet to see despite asking the CEO and scientists at Property Care Association and leading rising damp influencers.

Even if rising damp is misdiagnosed, the injection holes are unattractive, but more or less harmless on external walls so long as there is no subsidence (or risk of claim from neighbours – see image below). The problem is chemical damp proofers typically replace normal absorbent plaster with impermeable plaster – known as slurry – see the damage caused by slurry in examples below.

Damp from neighbours
Hygroscopic salts displaced by neighbour’s damp proofing treatment (without a party wall agreement).

Damp proofer’s slurry

British Standards Institute BS 6576 and Building Research Establishment BRE 245 and Property Care Association provides guidance; code of practice, replastering and salts. BSI, BRE and the PCA advocate only installing salt or water resistant plaster (slurry) if there are hygroscopic salts and only following sufficient time to dry out a wall after installing a chemical or physical DPC.

Example failed damp proofing treatment
Damp visible above damp proofer’s slurry

Slurry is the problem not chemical injections. 

  1. The time, risk and expertise is installing the salt resistant impermeable plaster (slurry), not injecting the damp proofing chemicals. A typical damp proofer’s quote for treating a length of wall is:
    • £500 for chemical injections
    • £5,000 for replastering.
  2. A damp proofer is not going to wait 6 – 10 months to determine if a wall remains damp after injections, when most of the profit would be delayed – see video at PCA conference below.
  3. Slurry can hide damp for a time, so even if rising damp is misdiagnosed, there is limited risk of come back.
  4. A damp proofers guarantee is only against rising damp, so if the actual issue is condensation, rain or a leak, then a guarantee is invalid.
  5. If rising damp is misdiagnosed, water is likely to continue, for instance form a leak, rainwater or condensation, then there is a risk of:
    • timber rot and woodworm,
    • moisture showing along the edges of the impermeable plaster,
    • water will eventually blistering and break through the new plaster.
  6. It is a waste of money £5,000 – £60,000 depending on the amount of wall deemed to need replastering.
  7. You may be liable to compensate neighbours for dampness displaced onto their wall.
  8. The work is messy and disturbing.
  9. There is likely to be disruption to the plaster where the old and new join – the interface (see the images on this page). This effect can be limited by replacing plaster across the whole wall, making it homogenous (but if you plan to replace plaster, then at least use thermal insulating plasterboard with a void and hygrometer behind the skirting board, to minimise the risk of rot).
  10. Furthermore the damp patch is likely to reappear behind the impermeable plaster if there is another source of water, and cost you more money when you come to sell the property.
Problem discussed at PCA conference.
Dry rot following misdiagnosed rising damp, the problem was a blocked gulley.

Hygroscopic salts

The movement of hygroscopic salts across a wall sits at the heart of the rising damp debate.

  • Why do salts form bands?
  • Given that hygroscopic salts are often found on first and second floors, do those salts necessarily come from groundwater. 
  • Do you know of any scientific papers on the subject of the movement of hygroscopic salts in walls – please email me?

From PCA guidance: Combustion gases in chimney flues contain traces of acids which form chlorides, nitrates and sulphates in the masonry. This is a common source of contamination at the surface of chimney breasts and reveals at all levels (upper floors as well as ground floor level). Other sources include: De-icing salts, water from soil contaminated with urine.

What are Hygroscopic salts

Hygroscopic salts are salts that attract water, causing it to condense at normal levels of relative humidity. The best-known hygroscopic salt is common table salt or sodium chloride, which if pure, becomes clumpy, sticking together when it is humid (above 75%RH – relative humidity). The most common hygroscopic salts on walls are calcium nitrate and calcium chloride that cause deliquescence, a form of condensation at relative humidities of about 50%RH and 25%RH, respectively.

Why are hygroscopic salts used to justify rising damp treatment?

So why are bands of hygroscopic salts used as justification for chemical damp proofing treatment? We don’t know the answer, but suspect it’s because no alternative diagnosis has ever has been provided – see our recommended evidence at the end of this page.

Horizontal & vertical hygroscopic bands either from animal urine or de-icing treatment.

A simple hygroscopic salt treatment

Hygroscopic salts are benign, that is they don’t cause rot or mould. They just don’t look great. They are normally deep within the wall, so some form of hiding is inevitable.

The easiest solution for dealing with hygroscopic salts is surprisingly simple. Cover them an oil based primer such as Zinsser, provide a large overlap, normally 300mm and apply more than one coat. The cost is low, and easy to reapply if ever required.

The simplest solution is to cover hygroscopic salts with an oil-based primer.

Rising Damp influencers

Both sides of the Rising Damp debate believe their arguments passionately. They are decent, well meaning people. So why don’t either side listen to each other and try to solve the conundrum scientifically with evidence.

In our opinion the reasons are financial and professional on both sides. It is almost as if neither side wishes to explore the debate logically with evidence. Rising damp diagnosis accounts for around £500 million each year, in either damp proofing treatment or home purchase fall-throughs. If it wasn’t for the fear of rising damp, then owners would be less willing to pay high prices for treatment, be that rising damp treatment or treatment recommended by an independent surveyor.

I have spend much time getting to know people from both sides of the debate.

  • Rising Damp advocates:
    1. PCA personnel (headed by Stephen Hodgson), instructors (headed by Graham Coleman) and Chemical damp proofing contractors honestly believe that rising damp is quite common. 
    2. They are so convinced by its prevalence, that there has been virtually no attempt to replicate rising damp and describe the risk factors causing it or common to rising damp. 
    3. Graham Coleman is the PCA’s leading instructors. View his YouTube case against rising damp deniers and judge for yourself if he makes the case for rising damp. In our opinion, scientific words are used and concepts are explained, but there is no attempt at providing reproducible evidence. I have attended numerous PCA lectures on rising damp, including given by Graham Coleman. At no point has rising damp been demonstrated practically. Photos of damp walls are said to be caused by rising damp, with no ability to study the walls, photos of the outside or reference to groundwater levels (I do the same, but would happily contact owners and show evidence to the PCA). 
    4. It is quick and easy to drill down into the ground to determine if the water-table is within about 500mm of a wall, or look up groundwater levels online or in local literature. If there’s no groundwater, then there can’t be rising damp. The height is seasonal, so this is best done in springtime.
  • Rising Damp deniers. 
    1. On the other hand, people like Jeff Howell (Telegraph journalist) and Stephen Boniface (former head of RICS surveying faculty) and Pete Ward (heritage property restorer) say rising damp is a myth, with similarly little reproducible evidence. 
    2. In our opinion they tend to grandstand with cursory explanation. Denying that water can rise-up a brick and past a mortar course, when it is easy to replicate and doesn’t help move the debate forward.
    3. Typically, they are dismissive of the electrical damp meter, which while it can’t identify the type of damp, is useful at detecting and profiling dampness https://youtu.be/KuoKhF31hL8

Property Care Association (or PCA)

The PCA represents chemical damp proofers. It is often deferred to by RICS homebuyer surveyors as the expert in rising damp. 

Damp along the top of damp proofer’s slurry.

Graham Coleman (PCA instructor)

Graham is or at least was the PCA’s lead instructor and has probably taught a majority of chemical damp proofers, as well as many independent damp surveyors. 

He comes across as very knowledgeable, see his recent YouTube recording of “Dampness in Buildings and diagnosis”. Graham defines rising damp as the “vertical movement of water through masonry, the water originating from groundwater”. In the “rising water there are dissolved salts”.

What is important is that the source of water is groundwater. The salts in Graham’s opinion, help diagnose rising damp.

Water from any source can rise

All water rises, whether it’s mainswater from a leak, condensation or rainwater. Most material will cause water to rise through ionic attraction. The rise is limited by gravity – weight. That is why the smaller the pore size, the lower the weight of water relative to surface area, and therefore the greater the rise – like capillaries.

  • Gravity mainly draws water downwards, through masonry.
  • Cold walls lose heat, increasing the risk of condensation.
  • Damp bricks increase heat loss.
  • That is why condensation and indeed penetrating damp and leaks can look remarkably like rising damp.
Rainwater penetrating render has caused water to pile up at base of this wall.
Why groundwater is important

Groundwater is the water under the water-table. A wall in contact with the water-table will absorb water upwards, as the soil under it is saturated. By contrast unsaturated soil will absorb water out of a damp wall, so the upwards absorption is limited to about 500mm above the water-table. Graham mentioned this in passing, without going into detail.

Damage along the line of damp proofer’s slurry.
Hygroscopic salts

Graham focuses on hygroscopic salts. Soil is normally rich in salts including hygroscopic salts of nitrate and chloride. Groundwater typically passes through soil, so it is likely to be high in salts. However, groundwater is not the only source of salts. For example plaster and mortar is full of calcium sulphate, also known as gypsum, which is not hygroscopic and therefore crystallises on the surface. Walls with significant condensation or rain issues are often coated in fluffy white calcium sulphate.

In his video, Graham states that that the presence of hygroscopic salts in a wall is almost unique to rising damp and “the key to its diagnosis, see  https://youtu.be/ys6T16R8xQ8?t=886

However, he appears to undermine this argument by finding hygroscopic salts on the first floor: “from the long-term burning of fossil fuels”. 

Hygroscopic salts on the first floor from a chimney breast.

Graham details the salt and water content of bricks up various walls and appears to conclude that any high chloride or nitrate concentration is a sign of rising damp. There is no evidence to support this. The mainswater is often high in nitrates and chlorides, at least Thameswater is.

Salt banding is complex, yet there are no scientific papers detailing it.

My experience with Rising Damp

I have seen some 3,000 walls with dampness mainly at the base of the ground floor. Not one wall could not be explained by another source of damp: rainwater, leaks or condensation. Not one was caused by rising damp. We don’t profit from any recommendations, so it doesn’t make any difference to us whether or not we identify damp as being rising damp or from a leak etc.

I came into damp surveying with no pre-conceptions about which side of the debate was correct. Before I trained and qualified as a PCA damp surveyor, I tested bricks and paper in water, so was aware that water could rise up a brick and had an idea about the pattern and extent of rise in paper. Over the years of damp surveying, I have listened to both sides of the rising damp debate, neither are convincing, neither side provide conclusive reproducible evidence, which is odd considering how widely the term is banded about.

We are constantly amazed by the damage caused by rising damp treatment.
I am constantly amazed by the damage caused by rising damp treatment.
My experience of hygroscopic salts

In my experience hygroscopic salts are mainly found by ground floor chimney breasts. However, the fact that they are found elsewhere, such as on the first floor, demonstrates that they are not necessarily as a result of groundwater rising up. Any water coming into contact with salts associated with chimneys, such as when a chimney is removed or replastered, is at risk of releasing hygroscopic salts.

The presence and location of hygroscopic salts is the clue to understanding rising damp. I have asked many experts at the PCA and elsewhere for scientific papers describing its movement, but understand that there are none.

PCA have so far refused a simple study into the movement of hygroscopic salts in a wall.
The PCA have so far refused a simple study into hygroscopic salt movement in a wall.
No one has ever studied the long-term movement of hygroscopic salts in walls. 

There is an argument to say, does it really matter if the problem is treated as rising damp when in fact it is condensation, rainwater or a leak?

Well no, see the examples of walls treated for rising damp on this page, when there was another source of mosture. We see examples of misdiagnosed rising damp at a majority of damp properties, at least in London. If anyone at the PCA asks for evidence, we will happily arrange access to support our claims.

This damp wall is after successive rising damp treatments. The problem was a leak.
This damp wall is after successive rising damp treatments. The problem was a leak.
Lack of reproducible evidence

At the heart of the problem, there is a lack of reproducible evidence, on both sides. The chemical damp proofers provide no evidence for rising damp, other than hygroscopic salts, but then don’t provide evidence of the movement of hygroscopic salts in walls.

The rising damp deniers stonewall, calling believers and damp proofing contractors names, rather than engaging in debate.

Damp on the walls of the Floating Palace - but what is the contribution from condensation?
Damp on the Floating Palace walls – does condensation contribute?

Diagnosing Rising damp for £15

The simplest way of determining if there is rising damp is to test for groundwater near to a brick wall. For groundwater to be in contact with walls, you need to drill below the level of the walls as near as possible, but away from services. A a rule of thumb, if there is liquid within 500mm of the ground level, then there is a risk:

  1. Taking great care to avoid drains, pipes and wires, drill a small hole about 1M below the ground level (1,000mm by 16mm drill bit £12.15),
  2. Place a long tube in the hole, I prefer clear plastic tube (clear plastic tubing £2.15), it is often worth placing a 1M long M6 threaded rod inside, to help push the plastic down. Leave the tube for 30 minutes or more.
  3. Pull the tube up rapidly, check the tube for evidence of water rising inside the tube by more than 500mm. If you are unsure you can push paper up the tube with about 10cm space at the base of the tubing.
  4. If water doesn’t rise inside the tube by more than 500mm then you don’t have a risk of groundwater and therefore no rising damp.
  5. If you have more than 500mm, then try the same thing in different locations. If the high varies, then you may have a mains water or drain leak. The height in the tube will rise as you get closer to the leak.
  6. If you have groundwater, there is a risk of rising damp.
    • It is then worth checking for a damp proof course.
    • Even if you have groundwater, but sufficient height above the water (1,000mm) or an effective DPC and sufficient sub-floor ventilation, then you wont be effected by rising damp.
  7. You can check the bedrock in your area and see if rocks contain groundwater: British Geological Survey. However, just because they do, doesn’t mean that there is a risk of groundwater coming into contact with the base of your wall.
Walls in this 15 century house are dry, despite being built over a water course and with no DPC.
The high walls and large sub-floor vents prevent rising damp.
Walls in this 15 century house are dry, despite being built with no DPC and over a water course.
The high cellar walls and large sub-floor ventilation prevent rising damp.

No rising damp without groundwater

This is where damp surveys become complex and interesting. For example:

  1. measure ventilation with an anemometer (in and out of a building),
  2. look for brown stains, a sign of penetrating damp or a leak, water picks up pigmentation as it passes through brick or over timber,
  3. test for leaks with a leak gauge,
  4. check rainwater goods for leaks,
  5. check neighbouring properties (above and below walls) for signs of dampness,
  6. test rainwater and foul water drains,
  7. check sub-floor relative humidity, or humidity of solid floors,
  8. use a damp meter (ideally in radio frequency mode) to determine the profile and centre of dampness),
  9. check for metal such as from RSJs, which may cause thermal bridges,
  10. look for evidence of past damp proofing treatment,
  11. install data loggers and
  12. use an infra-red camera to determining the temperature and surface relative humidity of walls over time.
This damp wall and rotten timber was treated many years ago for rising damp, yet the problem was drains causing condensation to form on the DPC. A £2.60 hygrometer probe saved £10,000.

6 thoughts on “Rising damp diagnosis”

  1. An interesting and balanced article on Rising Damp and the lack of research into slats in masonry. About time the BRE got back into the Rising Damp debate with a view to providing surveyors with definitive guidance – the current BRE digets 245 is now out of date.

    1. Thanks for your comment.

      Sadly, the rising damp debate is complex and polar with most people, professionals and the public, starting with preconceptions. This, in my opinion, reduces the chance of understating and solving damp issues. It would be good if someone independent, without preconceptions could replicate, study and provide a set on guideline on how to correctly identify rising damp. I doubt this will ever happen, as the money is in treating rising damp whether or not it is the root cause of dampness.

      1. Simon
        BRE 245 advises that walls built of porous masonry can (only) have rising damp where they:
        1) Stand in water or saturated ground, and
        2) Have been built without a physical barrier to the upward movement of moisture.
        However you seem to be saying that only ground water can cause rising damp, (ie a high water table).
        Am I understanding you correctly? as it seems to me that soil saturation from any source could lead to RD and I think this is what the BRED is suggesting?
        I would grateful if you would be kind enough to clarify this please – as when in doubt I tend to follow BRE advice.

        1. Alan,

          Thank you for reaching out with your query regarding the interpretation of BRE 245 and its application to identifying the causes of rising damp in buildings. Your understanding of the nuances of moisture absorption into porous masonry is critical, especially when considering the various sources of soil saturation and their impact on rising damp.

          BRE 245 indeed suggests that for rising damp to occur in walls built from porous materials, two conditions must be met: firstly, the walls must be in contact with water or saturated ground; and secondly, there must be an absence of a physical damp-proof barrier to prevent the upward movement of moisture. Your observation that soil saturation from any source could rise up a wall is astute and aligns with the broader interpretation of the guidance.

          I agree that groundwater (water beneath the water-table) is not the only definition of the source of water in rising damp. However, I choose to define rising damp as the upward rise of groundwater for many reasons:

          1) Water from any source will rise up an absorbent material, such as kitchen paper dipped in tap water. The rise of moisture is a symptom of damp, not a source or root cause.
          2) Sources of water other than groundwater, such as condensation, leaking pipes, overflow from rainwater goods, or high vapour levels in the sub-floor (often resulting from leaking drains), should and can be easily dealt with at their source.
          3) There is a tendency to treat every unresolved source of dampness at the base of a wall as rising damp by default because no other source can be found, not because the source is groundwater or indeed a DPC has been breached.
          4) Groundwater sufficiently in contact with a wall to cause rising damp, can be identified by drilling down about 1 metre on all four sides of a property (taking care not to damage wires or pipes) and leaving a tube to measure water levels. If the water levels are equal, then, and only then, there may be groundwater; otherwise, if one level is higher than another, it is probable that there is a leaking underground drain or similar source, which should be fixed to avoid the risk of rot or subsidence.
          5) The common method of treating for rising damp is not just injecting absorption-reducing chemicals (which I am not totally against, occasionally recommending them), but also the replacement of plaster with an impermeable “slurry”. This is the main issue as it hides the damp, rather than dealing with the root cause, risking worse problems later. Clearly, if, for instance, a neighbour or the local water board refuses to fix their leaking drain, then you may have no choice. But you should be aware of the risks and mitigate those risks, such as by legal notification and by increasing sub-floor ventilation.
          6) A common misinterpretation of rising damp is the presence of hygroscopic salts in a wall, which while they can on rare occasions come from groundwater, they normally results from burning coal or equine urine. Furthermore, hygroscopic salts are easy to remedy without replacing plaster.
          Overall, there is a tendency in UK to identify every damp issue at the base of a wall as rising damp, without evidence of groundwater. Testing to make sure the soil is saturated would be a good starting point, that would perhaps lead to more sub-floor leaks being detected and fewer insurance claims for subsidence – as well as fewer rising damp claims.

          1. Simon
            Thankyou very much for such a detailed and informative reply. I really cannot disagree with a single thing you have said. It really is a great pity that other surveyors do not
            adopt your objective approach. Hopefully one day sufficient research (perhaps by UKCMB) will be undertaken to fully clarify the rising damp debate once and for all.

  2. Thankyou for your detailed and informative reply. I think you have hit the nail on the head and I really appreciate you outlining how to test for groundwater. As you say there is a need for an authoritative and agreed guide which we can all rely on, but there are no signs of this on the horizon. In fact we dont even have an agreed definition for “rising damp.” I actually wrote to BRE suggesting they update the now old BRED 245 but they showed little interest and implied that they would only do this under government or other significant influence.

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