Is rising damp a myth?

The myth argument, put at its strongest

The case is most associated with Jeff Howell — a bricklayer, lecturer and long-running newspaper columnist — who argued in The Rising Damp Myth (2008) that rising damp in buildings essentially does not exist. His central experiment is easy to picture and easy to repeat: build a brick pillar, stand it in a tray of water, and watch the water fail to climb. He argued that the pore spaces in bricks and blocks are too coarse for meaningful capillary action, contrasting them with the very fine vessels in a tree, and that cement-based and most lime-based mortars will not pass water at all. He reported managing to produce rising dampness only once, using a mortar so weak it would never be used in real construction.

That is the laboratory half. The commercial half is stronger, and it is the half that has done the real damage to this industry's credibility. In damp proofing, the diagnosis is usually made by the business that sells the cure, at no charge, in a single visit, on the strength of one instrument. There is no other part of construction where that arrangement would pass without comment, and it should not pass here either.

The position gained genuine traction in Britain, and a former RICS chief has been quoted supporting the framing. It deserves to be answered on the evidence rather than waved away, so that is what the rest of this page does — starting with the parts where the critics are simply correct.

Five things the sceptics are right about

We are about to concede considerably more than a damp company is supposed to concede. Each of these is either published, documented in a government technical guide, or a straightforward consequence of how the instruments work.

• Over-diagnosis is rampant and commercially structured. The person deciding whether you have rising damp is usually the person who would be paid to treat it, and the visit is free precisely because the report is a sales document rather than a diagnosis.
• The instrument critique is correct on the physics, not merely on the ethics. A two-pin meter measures electrical conductivity between two pins. Soluble salts are electrolytes. A dry, salty wall reads higher than a wet, clean one, and the meter cannot separate them.
• The lookalikes really are more common than the real thing. Condensation, a bridged damp course, ground built up over the damp course, a blocked gutter or downpipe, a concealed plumbing leak, failed shower waterproofing and lateral damp from higher ground together account for the large majority of cases presented as rising damp. Archicentre Australia's own technical sheet puts about 70% of mould problems down to condensation and about 30% to rising damp.
• The treatment is frequently sold to people who did not need it — and where it does appear to have worked, the replastering that came with it may be doing whatever good is being observed, rather than the chemistry.
• Injection is routinely sold without any of the drainage and ground-level work that would have solved the problem for a fraction of the price. The Australian heritage guide sets out an explicit order of operations, puts damp-course insertion at step six of seven, and the industry sells step six to people who needed step two.

The instrument the whole argument runs through

Almost every rising damp diagnosis made in Australia is made with a two-pin electrical resistance moisture meter. It passes a small current between two pins and reports the conductivity between them. It is calibrated for timber, where the relationship between moisture content and conductivity is well characterised. Masonry is not timber, and masonry carrying a century of accumulated salt is not remotely close.

Soluble salts are electrolytes. A wall that is bone dry but salt-loaded conducts as well as, or better than, a wall that is genuinely wet and clean, and the meter has no way to report which one it is looking at. The Australian heritage guide records that it is common on salty walls to get readings above 100% moisture content — a figure that leaves no room in the sample for the masonry itself. Foil-backed plasterboard, buried cables, pipes, nails, conductive paints and carbon in some finishes all produce the same false highs.

The guide's caution box states it without hedging: moisture meters should never be used as the sole basis for diagnosing a damp problem, and never used on their own to prove that a wall is unacceptably damp. That is not a blogger's opinion. It is Salt attack and rising damp, written by David Young OAM and published jointly by the Heritage Council of NSW, Heritage Victoria, the South Australian Department for Environment and Heritage and Adelaide City Council, at Section 11.2. It is a free download, and we have not been able to find a single Australian damp contractor's website that cites it.

What capillary rise is, and how well it is actually quantified

Rising damp is groundwater drawn upward through the connected pore network of brick, stone, mortar or render by capillary suction. It is the same effect that pulls a spill up a paper towel: the finer the pore, the stronger the pull. It needs three things at once — liquid water in contact with the base of the wall, a continuous capillary path upward, and evaporation from the wall face. Break any one of the three and it stops. That is the whole mechanism.

In 2007 Hall and Hoff published a sharp-front model of it in Proceedings of the Royal Society A, deriving the steady height of rise from properties you can measure in a laboratory: the sorptivity of the material, the thickness of the wall, the evaporation rate from its face and the water content of the wetted region. Three consequences fall straight out. Height rises in direct proportion to how absorbent the material is. It rises with the square root of wall thickness, not with thickness itself. And it rises inversely with the square root of the evaporation rate — reduce evaporation and the damp climbs.

Note what is absent from that list. The depth or pressure of groundwater below the wall barely matters. Neither, to any real degree, does gravity: the same authors computed cases with no-gravity steady heights of 500 mm and 1000 mm and found that including gravitational drainage reduced them to about 488 mm and 951 mm. That is a 2–5% correction. The common objection that water cannot climb that far against gravity has been calculated, and the answer is that gravity was never the limiting factor. Evaporation is.

The worked example in the paper is a 150 mm limestone wall with a sorptivity of 1.0 mm/min^0.5 and an evaporation rate of 0.001 mm/min. It predicts a steady height of 0.61 m — squarely inside the range surveyors have been observing on real buildings for decades. Double the wall to 300 mm and the height only moves to 0.87 m, because of the square-root scaling. Quarter the evaporation rate and it doubles to 1.2 m. The Australian heritage guide gives the normal exterior limit here as 1.0–1.5 m above ground, with the active evaporative zone typically 0.5–1.2 m and very little evaporation below 0.3 m. At the extreme, Massari and Massari recorded 5.3 m of rise in the Church of San Bernardo in Rome — because that wall is 4 m thick, which is exactly what the model says should happen.

One more figure is worth carrying around, because it explains the damage rather than the wetness. At steady state the wall is not a static wet object; it is a slow pump. The 150 mm example moves roughly 0.88 litres per day per metre of wall length — about 320 litres per year per metre. A 10 m run of affected wall is therefore transporting on the order of 3,000 litres a year, and every litre leaves its dissolved salt behind. That flux, not the dampness, is what destroys masonry.

Why the brick pillar in the tray of water does not climb

The pillar experiment is real, repeatable and genuinely awkward for our industry, which is presumably why our industry has never answered it in public. It has an answer, and it is in the same Royal Society paper, in a section written specifically to address it.

It is difficult to replicate rising damp in the laboratory, principally because it is difficult to produce a mortar sufficiently sorptive. Fresh mortars, and cement-containing mortars in particular, act as a barrier to rising damp rather than a conduit for it. Mamillan and Bouineau's limestone test walls make the point neatly: rise halted at the first mortar joint even though the properties of the stone itself predicted far greater height.

Old walls behave differently, and the difference is time. Mortars become more sorptive over decades of continuous water passage through them. Gummerson's work showed that steady capillary flow through a single clay brick led to complete saturation only after about two years, as trapped air slowly diffused out — which means short laboratory tests systematically underestimate both sorptivity and long-term water content in real walls.

So a test pillar built with new mortar failing to wick is not a disproof of rising damp. It is precisely what the theory predicts. It tells you nothing about a 120-year-old lime-mortared wall whose joints have been transmitting water for a century.

And this cuts our way at least as often as it cuts theirs, which is the part nobody in this trade volunteers. A 2005 brick-veneer house, built on fresh cement mortar over an intact 0.5 mm polyethylene damp-proof course, is very close to being that pillar in the tray. When someone with a twenty-year-old house rings us about damp at the base of a wall, rising damp is near the bottom of our list before we have left the office.

In 2022 the damp industry's own trade body signed the critique

In September 2022 the Royal Institution of Chartered Surveyors, Historic England and the Property Care Association jointly published a position statement titled Investigation of moisture and its effects on traditional buildings: Principles and competencies. It was supported by Cadw, Historic Environment Scotland, the SPAB and the IHBC. That is a surveying body, a heritage regulator and the damp-proofing industry's own trade association, signing the same document.

Its two central principles are the ones that matter to a homeowner. Traditional solid-walled buildings do not perform like modern ones and should not be expected to. And the observation of moisture in an old building should not automatically be treated as a problem requiring a fix.

We should be straight about its limits. It is a British document about British buildings. It has no standing in Queensland, it is not an Australian Standard, and it does not tell you anything about your wall. What makes it worth citing is who put their name to it. When the trade association for damp proofing co-signs a statement saying moisture in an old building is not automatically a defect, the diagnostic critique has stopped being a fringe complaint.

The half of the argument that does not survive the flight from Britain

The myth argument is a British argument grown in a British climate, and the climate is doing more work in it than anyone admits. Our building tradition is British; our weather is not. Hotter, drier conditions drive far higher evaporation, and higher evaporation means far higher moisture throughput through the same wall — more litres a year, more salt delivered, faster decay. Combine that with genuinely saline Australian soils and younger Australian buildings can be in worse condition than far older northern European ones. The national heritage guide's phrasing is that the result is much higher rates of decay in this country than in the UK.

Adelaide is the national worst case: hot drying summers, very salty soils, and a housing stock of solid stone and brick much of which never had a damp course. It has been serious enough for long enough that the South Australian government established a Salt Damp Research Committee, which ran from 1974 to 1982, after the volume of complaints to consumer affairs about failed damp treatments. That committee is evidence for both sides of this argument at once. The problem was real enough to need one. The treatments were bad enough to need one too.

South East Queensland is not Adelaide, and the difference is not a small one. High ambient humidity here suppresses evaporation from the wall face. Because the steady height of rise goes as one over the square root of the evaporation rate, suppressing evaporation lowers the rate of decay — which is good — while raising the height the damp reaches, and pushing hygroscopic salt effects and condensation much further up the list of things it probably is. In practice: damp at the base of a wall in South East Queensland is more likely to be condensation, a bridged damp course, a downpipe, a leaking shower or slab-edge moisture than the same symptom in Adelaide, and on the occasions when it genuinely is rising, it can sit higher than the textbook figure suggests.

Which is why importing "it's all condensation" wholesale into an Australian context is its own diagnostic error, with its own victims. Treating the myth as settled means somebody with a genuine, progressive, structurally significant salt-damp problem gets told to open a window and comes back in ten years with 50 mm of mortar loss across five courses.

Why a damp company is comfortable saying most damp is not rising damp

Here is our scope, so you can weigh everything above against it. We do exactly two things. We inject a chemical damp-proof course into the mortar bed of external brickwork. And we grind back internal concrete slabs, prepare the surface and apply a Hydropoxy epoxy moisture barrier to the top of the slab before new flooring goes down. We are waterproofing and concrete repair specialists, not builders. We do not do landscaping, drainage, plumbing, subfloor ventilation, wet-area waterproofing, physical or saw-cut damp courses, undercutting, or render replacement.

So when the honest answer is that your garden bed sits 200 mm above the damp course, we have nothing to sell you. That is not altruism and we would rather not dress it up as any. It is that a job which was never going to work ends with our name on a wall that is still wet, and the jobs that work are the ones that get talked about. We would rather do the job that works.

Even where it genuinely is rising damp, injection is not the whole scope, and the industry's silence on this point is the single most predictable cause of unhappy customers. A correctly installed chemical damp-proof course forms a continuous water-repellent zone that capillary moisture cannot climb past. It does nothing at all about salt already in the wall above it. Sodium chloride goes wet at around 75% relative humidity, which is an ordinary humid day in South East Queensland. Calcium nitrate goes wet at roughly 47–55%. Magnesium chloride at about 33%, which is drier than an occupied Australian house realistically gets. Above about 0.5% salt by weight, desalination and replastering in lime is required as well — and that is masonry restoration work we do not carry out. We say so before the quote, not after it.

How to settle it on your own wall, in order

1. Go outside in heavy rain and watchFree, and it resolves more cases than any instrument. Watch the gutters, the rainwater heads, the downpipes, where the stormwater actually discharges, and which way the driveway and paths fall. Falling damp is worst high on the wall, which is the giveaway, and salt appears where water evaporates rather than where it got in — so trace it back deliberately.
2. Find the damp course, with a shovel if you have toThe NCC's Housing Provisions set a damp-proof course not less than 150 mm above adjacent ground level, 75 mm above finished paving that slopes away, and 50 mm where protected by a carport or verandah. The heritage guidance recommends 150–250 mm for a remedial course, with 200 mm as the ideal. Dig a small inspection pit and measure. A buried damp course is the most common genuine finding in Australian houses, and it is a bridging problem, not a failed-barrier problem.
3. Pull the garden bed back and fix the fallsLeave a sterile strip against the wall at least 300 mm wide, preferably more than 500 mm, surfaced in coarse gravel so rain cannot splash up and soil moisture can still evaporate to the sky. Move sprinklers to drippers kept at least 500 mm off the wall. Grade the first metre to fall about 25 mm away, with the low point 1.5–2.0 m out; AS 2870 and the NCC require a minimum fall of 50 mm over the first metre for slabs. On highly or extremely reactive clay sites, get engineering input before making large changes to soil moisture near footings.
4. Rule condensation in or out with a data logger, not a meterLog internal air temperature and relative humidity along with wall surface temperature for at least a full week including cold nights. If the surface repeatedly falls below the room's dew point, you have condensation, whatever any meter says, and no damp course on earth will change it. A fortnight to a month is more realistic than a week, and genuinely seasonal behaviour can need a year.
5. Only then, drillBS 6576 requires masonry samples; you cannot diagnose rising damp from the surface. The reference method is a vertical profile of six to eight samples per line, taken past the last visible sign of damp, at known heights and known depths — commonly 0–10, 10–20 and 20–40 mm — sealed immediately, weighed, oven-dried and reweighed for total moisture, then re-equilibrated at 75% relative humidity for hygroscopic moisture content. The shape of the gradient, with free water decreasing as you go up, is the actual evidence. Add salt speciation where salt attack is suspected; more than about 0.5% by weight is cause for concern.
6. Then wait a year before anyone injects anythingThe Australian guide is explicit: do not undertake insertion of any form of damp-proof course until all the basic housekeeping measures have been completed and their effectiveness assessed over a period of at least a year. There is a physical reason as well as a commercial one. The time to reach 95% of the steady height is about 31 days in the standard example but is inversely proportional to evaporation rate, so behind a coating or in a poorly ventilated space it can be years. A treatment judged a success at three months has proved nothing whatsoever.

What it costs

Questions we actually get asked

So is rising damp real, or not?

Real, quantified, and much rarer than it is diagnosed. Capillary rise through porous masonry is standard transport physics — sorptivity, unsaturated capillary flow, the Buckingham-Richards equation — and the sharp-front model published in Proceedings of the Royal Society A in 2007 predicts real-world heights from measurable material properties, matching British survey observations and Italian field data including a 4 m thick Roman church wall showing 5.3 m of rise. What is not defensible is the claim that every high meter reading on a wall base is rising damp. In modern housing with an intact damp course it is comparatively uncommon; in pre-damp-course masonry, and in houses where the damp course has been buried or bridged, it is genuinely common.

Does rising damp go away or dry out on its own?

The water can stop arriving; the salt does not leave. If the source is removed — the ground lowered, the garden bed pulled back, the downpipe repaired — free capillary water in the wall will fall away over months. The Australian guide puts drying at 3–6 months after replastering, and up to 12 months for wet thick walls; the old BRE rule of thumb of roughly one month per 25 mm of thickness puts a 230 mm solid wall at around nine months. But the salt delivered over decades stays in the pores, and hygroscopic salts pull moisture straight back out of the air. That is why a wall with no live source at all can read damp on a meter permanently, and why acceptance should be judged on drilled-sample free water rather than on a meter.

Is rising damp a structural defect, or just cosmetic?

It can become structural, but slowly, and the timing is counter-intuitive. Salt-attack decay follows an accelerating curve rather than a straight line: salts accumulate for decades filling the pore space with almost no visible damage, and then deterioration speeds up sharply. The Australian guide's notional curve shows around 80 years of near-nothing followed by rapid acceleration, so a building that has looked much the same for a century may be twice as damaged after another ten years. Mortar loss of around 50 mm across five to ten courses puts you at risk of local collapse of the brickwork, and that is a now problem. What it is not, at any stage, is an emergency in the sense the advertising implies. This process is measured in decades.

Is rising damp common in Queensland houses?

Less common than the marketing suggests, and less common than in South Australia. Much of the South East Queensland housing stock works against it: high-set timber on stumps has no continuous capillary path from ground to wall, and brick veneer and slab-on-ground built from the 1960s onward generally has an intact polyethylene damp-proof course. Where we do find genuine rising damp here it is usually pre-1930 solid brick, or a house of any age where the damp course has been buried by later landscaping, paving or render. Our humidity also changes the picture: it suppresses evaporation, which lowers the decay rate but raises the height of rise and makes hygroscopic salt and condensation far more prominent in the differential diagnosis.

My building and pest report says "high moisture readings consistent with rising damp". Is that a diagnosis?

No, and a competent inspector would not claim it is. A pre-purchase inspection is carried out under AS 4349.1 and is not a damp investigation; it is a visual inspection with a hand-held meter, done to a tight time budget, and the phrase "consistent with" is doing a great deal of work. It is a reason to commission a proper investigation before you negotiate on price, not a reason to accept a treatment quote. A damp investigation can be commissioned as an inspection of particular technical aspects under AS 4349.0, which gives it a defined scope and reporting framework.

If most cases are not rising damp, why does a rising damp company exist?

Because the minority of cases that are real are expensive, progressive, and almost never fixed by the cheap options. Nine of ten enquiries we take are better solved by a drainage contractor, a plumber, a landscaper, a licensed waterproofer or a $40 spirit level, and we say so. The tenth is a genuinely salt-loaded, genuinely rising wall where source control has already been done and monitored, drilled samples show free water decreasing with height, and a chemical damp-proof course into the mortar bed is the correct next step. That is the job we are for. Doing the other nine badly is how the industry earned its reputation.

Can rising damp be fixed?

Where it is genuinely present, yes — with conditions worth being clear about. Removing the source comes first, and in a substantial proportion of Australian cases source control alone resolves it. Where a barrier is genuinely needed, a correctly installed chemical damp-proof course forms a continuous water-repellent zone that capillary moisture cannot climb past. But it does not remove salt already in the wall, it does not resist water under pressure, and it does not dry the wall for you. Where salt exceeds about 0.5% by weight, desalination and lime replastering has to happen too, or the masonry keeps decaying above a technically successful damp course — which is exactly the outcome documented in the Australian guide.