When a damp course is not the answer

Thirteen things that get called rising damp

Every one of these presents as damp low on a wall. Several of them produce a level line, salt bloom and a high meter reading, which are the three things most commonly offered as proof of rising damp and which, on their own, are also produced by things that are not rising damp.

Number twelve on this list is genuinely common around here. That is the point people miss when they read a page like this as debunkery. Rising damp is real, and on this coast it is common. The aim is not to argue you out of a diagnosis, it is to make sure the diagnosis matches the wall. The right-hand column is where the money is.

A good inspector separates these on site, in an hour, from the outside in: ground levels against the damp course, where the water lands and where it goes, salt banding, and the height and shape of the damp. That is a real diagnosis, and most walls never need anything more elaborate than it.

The eight, and what actually fixes them

These are the ones where the correct answer is a different trade. Indicative Australian ranges are given because a number is the only thing that makes the comparison real, and because a homeowner who knows what a corrected garden bed costs is much harder to sell an unnecessary injection line to.

None of this is an argument that your wall is one of the eight. It might well be row twelve. It is an argument for knowing which, before the money moves.

Why the cause matters more than the label

Nearly everything that goes wrong in this trade goes wrong at the same point: the label is right and the cause is wrong. The wall really is damp, the damp really is rising, and the water is arriving because a paver was laid over the damp course in 2003. Inject that wall and you have installed a barrier below the level the water is now entering at. The invoice is real, the work is real, and the wall stays wet.

That is the reason a diagnosis is worth more than a treatment recommendation, and it is why the site visit spends most of its time outside. Ground levels against the damp course. Where the downpipes discharge. Whether the paving falls toward the house. Whether the subfloor vents are still open or have been rendered flat. The wall itself is often the least informative thing on the site.

Now the instrument, because it gets argued about more than it deserves. A two-pin resistance meter measures electrical conductivity, and soluble salts are electrolytes, so a dry but salty wall can read as high as a genuinely wet one. Readings above 100% moisture content turn up regularly on salt-loaded masonry, which is a physically impossible figure that leaves no room for the bricks. The Australian heritage guide's caution is explicit: moisture meters should never be used as the sole basis for diagnosing a damp problem. That is a caution about weight, not a reason to leave the meter in the van. Used alongside ground levels, drainage and the shape of the damp line, it is a useful input. Used as the entire case, it proves nothing much either way.

Then there is the time lag, which is the part that lets bad scoping survive. A damp wall does not react quickly. The modelled time to reach 95% of steady height is about 31 days in the standard example, but it scales inversely with evaporation rate, so behind a coating it runs to years. Render a 215 mm wall to 1.25 m and the damp front re-stabilises above the render after roughly 425 days. A treatment assessed at three months has proved nothing whatsoever. The reckoning is deferred by a year to three, not avoided — which is why it is worth being fussy at the start rather than hopeful at the end.

And when the reckoning arrives, the answer offered is generally that the salts are historic. Sometimes that is even true, because a chemical damp course genuinely does nothing about salt already above it, which keeps dissolving in humid weather and re-crystallising in dry weather and keeps breaking the masonry down. The heritage guide illustrates exactly that case: brickwork continuing to decay above a chemically injected damp course because the salts were left in place. Its seventh key step exists for that reason, and desalination belongs in the scope from the beginning rather than as a second visit.

None of this is speculation. South Australia ran it once already. So many complaints were made to consumer affairs about failed damp treatments that the state government established a Salt Damp Research Committee, which operated from 1974 to 1982. That is the official record, in the state with the biggest genuine salt damp problem in the country — a state, note, where the answer was almost never that salt damp was imaginary.

Who is looking, and what they are selling

There is a structural point worth making calmly, because it applies to everybody in this subject. The party performing the diagnosis is usually the party that would perform the cure, and in this trade that party usually specialises in a small number of cures.

The national heritage guide addresses it directly. When a homeowner asks which treatment to use, its answer begins by calling that the wrong question, and continues: be aware that many damp-proofing contractors specialise in one treatment method only, so seek independent advice. Its list of dos ends with: do get independent advice, that way there should be no pressure to use a particular product or system.

Professional guidance says the same thing about disclosure. Where a surveyor's recommendations may include sales, the conflict should be declared so the client understands the assessment is separate from the quotation.

So here it is, in the same size type as everything else. This site publishes research and holds no building licence. It does not inspect, drill, inject, quote or treat anything. The trade it points at sells chemical damp-proof courses and epoxy slab barriers, which is a commercial interest in the answer being yes — theirs, not this site's. Everything here is written to be checked against published sources rather than taken on trust, and the sources are named so the reasoning on this page can be checked as easily as anybody else's.

The practical consequence for you is simple. A free look from a contractor who does the work is an efficient way to find out what is wrong with your wall, and on most houses it is all that is required. The moment the answer has to convince somebody other than you — a builder, an insurer, a seller, a tribunal — a different kind of evidence is needed, and it should come from somebody with nothing riding on the outcome.

The numbers not published here

The obvious move on a page like this is a statistic. Some percentage of the waterproofer's inspections ending in no damp course recommended, printed large, updated quarterly. It would be the single most persuasive object on the website.

None is published here, and the same rule applies in the other direction — you will not find a made-up figure on this site for how many Gold Coast houses have rising damp either, however useful such a figure would be. A number like that would be self-issued: unaudited, unverifiable, and free to move in whatever direction the marketing needed in any given quarter. There would be no way to check it. A number you cannot check is decoration wearing the costume of evidence, and this entire site is an argument against exactly that.

What can be asserted is the mechanism, because it is checkable against a real house and against published sources. Shallow, often saline groundwater under low-lying coastal and reclaimed land. Marine aerosol and saline soils putting chloride into masonry. Rain that arrives in volume. Older brickwork with the ground built up over the damp course. Those conditions produce rising damp, they are ordinary here, and none of that requires a percentage to be true.

The structure of the diagnosis is publishable for the same reason: you can run it yourself. Thirteen causes. Eight that point at another trade. Three more that are still not the waterproofer's. Two that end in an invoice from a licensed waterproofer. The rules that separate them are on this page and in the diagnostic, they are deterministic, and the same answers always produce the same result.

And the list of things that get quietly reduced under price pressure is always the same one: drill hole diameter and spacing, hole depth, fluid volume per linear metre, and which faces of the wall were treated. Those are the figures nobody can inspect once the holes are plugged, which is exactly why they belong in the written scope before anybody starts. Getting them onto the quote is worth more than any percentage this page could print, because a job can be held to a number on a page.

The two cases where the answer is a licensed waterproofer

It is worth being equally specific about the other side, because a page that only says no is just a different kind of sales pitch — and on this coast, no is frequently the wrong answer.

Rising damp is real. The mechanism is published physics, the model predicts observed heights from measured material properties, and it reproduces field data from Britain to a 4 m thick church wall in Rome showing 5.3 m of rise. Australian conditions make it more consequential here, not less: higher evaporation drives far greater moisture throughput through the same wall, and saline soils mean every litre delivers more salt. The heritage guide's summary is that this produces much higher rates of decay in this country than in the UK. When it is genuinely happening, treating it is the right call, and the decay curve gives you a reason not to wait indefinitely.

1. A chemical damp-proof course to external brickworkThe case for it looks like this: solid or cavity brick, a level damp line under about 1.5 m, present all year rather than following rain, salt banding at the upper edge, and the other twelve causes looked for and excluded rather than assumed away. Ground levels corrected or being corrected as part of the same programme, gutters, stormwater and wet areas checked, and the housekeeping given time to show its effect — the heritage guide sets that period at a minimum of a year. Where the case is contested, or where somebody else has to be convinced, drilled samples and laboratory moisture and salt analysis settle it; on a straightforward wall they are not usually necessary. Correct execution is 10 to 15 mm holes at about 120 mm centres, drilled to within about 30 mm of the far face, gravity fed or injected at low pressure, with the header course drilled by preference on a 230 mm wall or both faces treated where a stretcher course is used.
2. An epoxy moisture barrier to an internal concrete slabThe case for it is narrower and it is a flooring question. New floor covering is going down over a slab that is still passing moisture, confirmed by in-situ relative humidity probe testing to ASTM F2170 at 40% of slab depth, which AS 1884:2021 makes the normative method with acceptance commonly stated at 75% RH unless the flooring manufacturer sets a stricter limit. The slab is ground back to sound clean concrete and an epoxy film is applied so the adhesive and the covering do not fail. It is a negative-side treatment: the water is still under there. It does not fix drainage, ground levels or a missing membrane, and a licensed waterproofer will say so rather than let it be inferred.
3. What a licensed waterproofer does not do, and will hand offPhysical damp courses by slot saw or undersetting, undercutting, desalination and poulticing, render removal and replastering, repointing, landscaping and excavation, site drainage and agricultural drains, roof plumbing, general plumbing, subfloor ventilation, and wet-area waterproofing. A licensed waterproofer is waterproofing and concrete repair specialists, not builders. Where one of those is the right answer — and across the thirteen causes it often is — they name the trade and stop.
4. What a licensed waterproofer will not install at allPassive electro-osmosis, which is an earthed copper strip in the wall. Water movement through a porous medium creates the electrical potential, not the other way round, so earthing the resulting charge cannot prevent capillary rise, and the national guide lists it among old treatments that should no longer be considered. Also damp-proof paints and water-repellent coatings on a wall with active rising damp, and hard cement render over a damp wall — all three reduce evaporation, which raises the height of rise, and trap salt at the interface.

What to ask any damp contractor before you sign

This is the part worth printing. It applies to a licensed waterproofer exactly as much as to anybody else, and every item on it is drawn from a published standard or a government guide rather than from an opinion about the industry.

None of these questions is aggressive and none of them is unreasonable to answer. Somebody confident in their diagnosis will talk you through all of it happily, and the ones who cannot are telling you something useful.

• Ask what they looked at outside. Ground and paving levels against the damp course, garden beds, where the downpipes discharge, how the ground falls in the first metre, and whether the subfloor vents are still open. A diagnosis made entirely indoors has skipped the most common way rising damp starts on this coast.
• Ask which of the other twelve causes were considered and how each was excluded, with the exclusion named rather than assumed. Meter isolation, flood testing, dye testing, CCTV and a borescope in the cavity are the tests; a glance from the driveway is not one of them.
• Ask them to describe the damp line and say why its shape points where they say it does. Level, under about 1.5 m and present year round is the rising damp pattern. A vertical stripe, a localised patch, or damp worst at the top of the wall is a different problem wearing the same clothes. An experienced inspector reading ground levels, drainage, salt banding and the height and shape of the damp is doing real diagnostic work, and it is reasonable to ask them to show their reasoning out loud.
• Ask for external ground, paving and garden bed levels measured against the damp course, in millimetres rather than by eye. The code minimums are 150 mm above finished ground, 75 mm above paving that slopes away, and 50 mm where a carport or verandah protects the wall.
• Ask whether the cavity and the subfloor were looked into. The national guide devotes a whole section to damage caused by damp-proofing work endangering floor timbers below, and requires an underfloor inspection as part of both investigation and certification. A borescope also converts a presumed rising damp case into a bridged cavity in about ten minutes.
• Ask what happens to the salt. Where a wall is blooming, the working threshold for concern is about 0.5% by weight, and the species points at the source: nitrate at a sewer, a fertilised bed or a former stable; chloride at groundwater, sea spray or acid cleaning; magnesium sulfate at contaminated bedding sand. Salt left in a wall keeps cycling long after the water stops.
• Treat any meter reading as one input among several, and expect whoever is holding it to say the same. It measures conductivity rather than water, salt reads high, and figures above 100% moisture content are common on salty masonry. The heritage guide is explicit that a meter must never be the sole basis for a diagnosis. Alongside levels and drainage it is genuinely useful; a photograph of a reading offered as the whole case is not.
• If the answer is contested — a dispute, an insurer, expert evidence, a house you are about to buy, or two competent people who have looked and disagreed — that is when drilled samples and laboratory analysis earn their cost, and they should be commissioned from somebody who does no rectification work.
• Know what that investigation involves before you commission one, because it is a real piece of work: drilled masonry samples to BS 6576, a vertical profile of six to eight heights taken past the last visible sign of damp, depth intervals at each height, commonly 0–10, 10–20 and 20–40 mm, oven-dry moisture content, hygroscopic moisture content measured at 75% relative humidity and reported separately so free capillary water can be obtained by subtraction, and salt species and percentage by weight. BRE Digest 245 is built on that comparison, and it is the analysis that separates a wall that needs a damp course from a wall that needs the salt taken out of it.
• Ask for the prerequisites sequenced ahead of the injection line rather than after it, and ask directly how the guide's instruction is being handled — do not insert any form of damp course until the basic housekeeping measures are complete and their effectiveness assessed over at least a year.
• Ask for the injection specification as numbers in the scope: hole diameter of 10 to 15 mm, spacing of about 120 mm, depth to within about 30 mm of the far face, gravity feed or low pressure, and fluid volume per linear metre stated as a figure. Injection above about 1000 kPa is a defect, not a feature — it blows out weak mortar and causes viscous fingering, where the fluid races ahead in fingers and leaves untreated gaps.
• Ask which faces are being treated. On a 230 mm one-brick wall the header course should be drilled by preference; where a stretcher course is used, the stretchers on the other side must also be treated. Treating one face of a wall that needed both leaves half a barrier, and it looks identical from the street.
• Ask for the product name and its active-ingredient content, not the word silane. Active content varies from around 15% to around 80% between certified products, and low-strength formulations have still obtained certification.
• Ask for desalination in the scope wherever salt is above about 0.5% by weight, and ask what is meant to happen to the salt if it is not there. Injection can also displace saline moisture upward into masonry that was previously undamaged, which is why a poultice should be applied at the same time as the injection rather than afterwards.
• Ask about the drying period before finishing: typically 3 to 6 months, up to 12 on thick walls, and no wallpaper for at least 12 months. A room handed back next week is a scheduling promise, not a technical one, and repainting early makes bubbling close to certain.
• Ask for the guarantee's exclusions as an actual document before you ask about the number of years. Read specifically for blocked gutters, a garden bed rebuilt against the wall, extensive repointing over the treated course, a sealer applied to the wall face, and condensation. Several of those are entirely reasonable maintenance obligations — the problem is finding out about them afterwards.
• Check the licence number on the QBCC public register before you sign anything. Building work in Queensland above a dollar threshold, commonly stated as $3,300 including materials and GST though you should confirm the current figure with the QBCC, requires a licensed contractor and triggers Home Warranty Scheme insurance.
• Treat a per-metre rate well under about $100 as a question rather than a saving. The guide names two of the mechanisms in print: diluting the fluid with additional solvent, and spacing the drill holes wider than recommended. A third is treating one face of a wall that needed both. All three are invisible the moment the holes are plugged, and nobody can inspect the result afterwards — not you, not a building inspector, not the contractor who plugged them.
• Ask one final question, and listen carefully to the answer: what would you tell me if it turned out not to be rising damp, and what would you recommend instead? Somebody who has thought about the other twelve possibilities will have an answer ready.

Where this leaves the reader

A licensed waterproofer is a waterproofing and concrete repair specialist, not a builder, and they perform two treatments. Where one of those two is genuinely the right answer the trade would very much like the job, and where it is not, an honest contractor says so. The inspection normally carries no charge either way, which means finding out costs a morning.

The failure mode in this trade is not the no-charge look. It is the visit that never leaves the lounge room: where the answer was decided before anybody checked the ground levels, where the scope of works is one line with a price under it, and where the guarantee quietly excludes the thing that was actually wrong. The only way to demonstrate that you are doing it differently is to publish the working — the causes, the tests, the numbers, and the eleven outcomes on this page that are somebody else's phone number.

If you are holding a quote and this page has made you uneasy, that is a reasonable place to be, and so is the opposite. The quote may be perfectly sound and the wall may be exactly what it says it is. The checklist above works on any contractor, and it works on a licensed waterproofer. Use it.

What it costs

Questions that actually get asked

Why would a damp company tell me I do not need a damp course?

Because a damp course installed against the wrong cause does not work, and the customer finds out. If the water is arriving over the top of the damp course from a paver or a garden bed, a barrier installed below that level changes nothing — the wall stays wet, the render blows again, and the person who sold it owns the argument for the next decade. The diagnostic visit is free whichever way it lands, so the cost of attending is the same whether the recommendation is an injection line or a downpipe bracket. The honest description of the arrangement is that it points at two treatments and spends a lot of time telling people they need neither of them. That is not modesty. It is what happens when the recommendation has to hold up for years rather than until the invoice clears.

Ya licensed waterproofer must turn away a lot of work. How much?

No percentage is put on it here, and the reason is worth stating rather than inventing a number. Any figure published here would be generated here, reported here, impossible to audit, and free to drift in whatever direction the marketing needed. A number that cannot be checked is decoration. What is published here instead is the structure, because anyone can run it: thirteen causes, eight of them pointing at another trade entirely, three more that are still not the waterproofer's, and two that end in an invoice from a licensed waterproofer. The rules that separate them are deterministic and they are set out in full on this page. The same rule rules out a made-up figure for how much rising damp there is on the Gold Coast — the conditions that cause it are checkable, and a percentage would not be.

The inspection was free and they found rising damp in twenty minutes. Should that be suspicious?

Not on either count by itself. Experienced people read patterns quickly, and around here a level damp line at the base of an older brick wall, present all year, with salt banding at the upper edge, really is the pattern — rising damp is common on this coast rather than exotic. What twenty minutes should still include is a walk around the outside: ground and paving levels against the damp course, garden beds, where the downpipes discharge, and whether the subfloor vents are open. Ask what they found out there, and ask what they excluded and how. If the answer covers the outside of the house as well as the wall you are both standing in front of, twenty minutes is plenty of time. If the entire case is a photograph of a meter reading, work through the rest of the questions on this page before you sign anything.

I already paid for injection and the wall is still crumbling. What happened?

Most often a scoping failure rather than a product failure, and it is one of the more predictable outcomes in this trade. A chemical damp course stops water rising. It does nothing at all about the salt already in the wall above it, which keeps dissolving in humid weather and re-crystallising in dry weather, and every cycle breaks the masonry down a little further. The Australian heritage guide illustrates exactly this case — brickwork continuing to decay above a chemically injected damp course because the salts were left in place — and its seventh key step exists because damp course insertion alone is not enough. The other common version is that the water was never rising in the first place and is still arriving over the top of the barrier from a garden bed or a downpipe, in which case the fix is outside. Where it is disputed, a drilled profile with hygroscopic moisture content reported separately settles which of the two you have: if free water is now negligible and salt content is high, the damp course is working and salt is the remaining problem, which is a different scope and a different trade from another round of injection.

What if more than one of the thirteen is happening at once?

That is common, and it is the main reason the sequence matters more than the label. A blocked downpipe, a buried damp course and a shower membrane failing on the other side of a wall can all be running at the same time, with genuine rising damp underneath them, and each one will happily take the credit for the others' symptoms. The published method deals with it by ordering the work rather than by picking a winner: correct the water sources first, then watch. The national guide builds in a review of at least a year before proceeding to damp course insertion, specifically to account for storms, floods and drought moving the readings in both directions. It is also why a treatment judged successful after three months proves nothing — the modelled lag behind a coating runs to years, not weeks.

If inspections are free, when would anyone pay to investigate?

When the answer has to survive somebody hostile reading it. A building dispute, an insurance claim, expert evidence, a contested pre-purchase decision on a house you are about to buy, or a wall where two competent people have looked and reached different conclusions. In those situations you want findings that are not attached to a repair anybody wants to sell you, which means forensic investigation: drilled masonry samples at several heights and depths, oven-dry and hygroscopic moisture content, and salt species and percentage by weight. an investigation-only consultancy is a separate waterproofing consultancy and forensics practice that does exactly that and performs no rectification at all, which is precisely why its findings carry weight in an argument. For an ordinary damp wall on an ordinary house, it is more than you need — the site visit and an honest look at your ground levels will get you there.

Can I use your checklist on a licensed waterproofer?

Please do, and it is the reason it is written the way it is — every item cites a standard or a government guide rather than an opinion, so it works on anybody. Ask them to describe the damp line and justify the shape, ask what they checked outside, ask which of the other twelve they excluded and how, and ask for hole spacing, hole depth, fluid volume per linear metre and which faces are being treated to appear in the written scope before anybody starts. If any of that cannot be answered, say so out loud. And apply the same list to every quote on the table, because a checklist applied to one contractor and not the others is not a comparison, it is a preference.