The method three state governments published and nobody cites

Where the method comes from

The guide is not a marketing document and nobody in this trade commissioned it. It came out of a body of Australian work on salt damp that includes the South Australian Salt Damp Research Committee, which ran from 1974 to 1982 because enough South Australians had complained about the treatment they had been sold that a government stood a committee up about it.

Its central argument is a sequence rather than a product. Salt attack needs four things at once — permeable masonry, available moisture, available soluble salts, and evaporation. Remove any one and decay stops. In practice none of the four can be removed completely, so remediation is always about reducing several factors rather than eliminating one, and the cheapest factor to reduce is almost always the water supply at the base of the wall. That is drainage, ground levels and gutters. It is not masonry work and it is not ours.

The reason this sequence is worth publishing rather than simply following is that the order is where the money is. A chemical damp course at step six, installed on a wall whose problem was at step two, does not fail visibly. The wall keeps doing whatever it was doing, and two or three years later everybody is arguing about a product that was never the answer.

What gets measured before anyone forms an opinion

Pattern and geometry are more diagnostic than any instrument. Genuine rising damp is continuous along the base of a wall, has a defined upper limit — typically 1.0 to 1.5 metres in Australia, with the most active evaporation zone between 0.5 and 1.2 metres — and correlates with ground level, damp course position and site drainage. So the first pass is structured looking: inside, outside, subfloor, cavity, roof and drainage, ideally on more than one visit and not only after rain, because rain washes surface salt away and hides the evidence.

Then the instruments, each of which settles one question and not others. The table below is the hierarchy we work down, and it is worth knowing which row a contractor stopped at before they quoted you.

Separating salt-held water from free water

This is the one measurement that decides which of two very different jobs you are looking at, and it is a subtraction rather than a reading.

Samples are drilled from known heights and known depths — commonly 0 to 10, 10 to 20 and 20 to 40 millimetres — six to eight heights per vertical line, taken past the last visible sign of damp. Mortar is sampled in preference to face brick or stone because it is less disfiguring, unless the mortar is markedly less permeable than the units, in which case salts concentrate in the units and those are sampled instead. Samples are sealed immediately in airtight containers, weighed, oven-dried and reweighed. Loss of mass gives true moisture content by dry weight.

The same oven-dried samples are then equilibrated in a controlled 75 per cent relative humidity atmosphere and reweighed. The mass they regain is the moisture their salt content will hold from the air alone: hygroscopic moisture content. Total moisture minus hygroscopic moisture is free capillary water, and free water that decreases as you go up the wall is the evidence for rising damp. Nothing else is.

Two results, two entirely different scopes. Free water present and decreasing with height means a live source, and once the prerequisites have been corrected and monitored, a damp course is the right conversation. High hygroscopic moisture content with negligible free water means a salt-contaminated wall with no live source — the damp was cured years ago and the salt stayed. That wall needs desalination and replastering, and a damp course would be spent on the wrong problem entirely.

Salt speciation runs alongside it, because the species points at the source. Heavy nitrates suggest a leaking sewer, animal urine from a building that was once a stable, or fertiliser from a garden bed against the wall. Heavy chlorides suggest groundwater, sea spray, or acid cleaning that somebody did to remove efflorescence. Magnesium sulfate can indicate contaminated bedding sand under paving. Above about 0.5 per cent salt by weight is cause for concern and reason to bring desalination into the scope.

Removing the cause — which is where a great many of these jobs end

What comes out of the testing is not a quote. It is a prerequisite schedule: what has to be corrected, in what order, by which trade, before any damp course is worth discussing. We do not quote step six on the same visit as step two, and we do not perform the prerequisite work, which is the arrangement that lets us write the schedule honestly.

The schedule is drawn from the same short list every time, because the causes really are that repetitive. Ground and paving levels, so the damp course sits 150 to 250 mm above finished ground with 200 mm the recommended target, against the NCC minimum of 150 mm above adjacent ground level. Garden beds pulled back to leave a sterile strip at least 300 mm wide and preferably over 500 mm, surfaced in coarse gravel, with drippers kept at least 500 mm off the wall. Falls corrected to about 50 mm over the first metre with the low point 1.5 to 2.0 metres out. Gutters, downpipes, rainwater heads and flashings. Concealed supply, waste and sewer leaks, air-conditioning condensate lines and irrigation. Wet-area membranes to AS 3740:2021. Subfloor ventilation to NCC Housing Provisions Part 6.2.

One caution goes on every schedule that involves drying soil near footings. On highly and extremely reactive clay sites — Class H and E under AS 2870 — large changes to the soil moisture regime near footings can cause shrinkage and structural cracking. That trade-off is named explicitly in the heritage guide and it needs geotechnical or structural input rather than enthusiasm.

Then the wall is left alone and monitored for at least twelve months, re-sampled at the recorded locations, with dates. Twelve months is not caution for its own sake: storms, floods, drought and seasonal humidity all move the readings, and a long dry spell can look exactly like a successful treatment. A meaningful share of properties never proceed past this stage, and when that happens the masonry line on the invoice stays at zero.

Then, and only then, the damp course — and what we publish about it

If drilled samples still show free water rising after the prerequisites have been corrected and held for a year, and the masonry is sound enough to take the treatment, this is where a chemical damp course belongs. It is the only masonry step in the sequence that is our work.

The chemistry is a silane or siloxane, delivered either as a high-solids water-based cream by cartridge gun or as a solvent-borne fluid at roughly 5 to 7 per cent by weight, gravity-fed or injected at low pressure. It diffuses through the pore structure and reacts with the substrate to line the pores with a hydrophobic silicone resin. It does not plug the pores, so the wall still breathes and still dries. Active ingredient content varies from roughly 15 per cent to roughly 80 per cent between certified products, which is why the product certificate matters more than the category name.

Every number below goes on the job record, and the record goes to the owner. A method you cannot audit afterwards is not a method.

1. Set out the courseHeight fixed at 150 to 250 mm above finished ground, 200 mm being the recommended target, and below all floor timbers. On a 230 mm one-brick wall the header course is drilled by preference; where a stretcher course is drilled instead, the stretchers on the far side must also be treated, either from the opposite face or by re-drilling through the same holes in a second phase. Never drill and impregnate directly into an existing tar-and-sand damp course — it may be underperforming, but perforating it does not help.
2. DrillHoles of 10 to 15 mm diameter at roughly 120 mm centres, which is about eight holes per linear metre, into the mortar bed rather than the brick face, to within about 30 mm of the far face of the wall. Slow speed, on-tool dust extraction, and the hole record kept as drilled rather than as intended.
3. Deal with voids firstThick walls, rubble walls and walls with poorly filled collar joints swallow product without forming a continuous zone. Voids are grouted before any chemistry goes in. Where the masonry is weak and crumbling, injection is not attempted at all — that is repointing work first, by a repointing contractor, and the treated course may need re-treating once the new mortar has cured, because extensive repointing can bridge it.
4. Introduce the productCream delivered by cartridge gun through a tube to the back of the hole; or fluid gravity-fed from feeder bottles refilled three or four times over about 24 hours; or low-pressure injection between roughly 150 and 500 kPa. Pressure above about 1000 kPa is a defect rather than a feature: the fluid advances as fingers, leaving untreated gaps between them, and it can blow out weak mortar.
5. Verify, and over-apply deliberatelyPenetration is checked by observing product appearing at inspection holes above the drilled line where the method allows it. The volume actually used is recorded per linear metre against the manufacturer's stated rate. Good practice is to deliberately over-apply to be certain of penetration, because the two documented responses to cost pressure in this trade — diluting the fluid with extra solvent, and widening the drill spacing — are both invisible from outside the wall for years.
6. Poultice at the same time where salt is presentInjection can displace saline moisture upward into masonry that was previously undamaged, so where salt exceeds about 0.5 per cent by weight, desalination should already be underway. That work is carried out by a restoration or conservation trade, not by us, and it runs $80 to $250 per square metre and is iterative — re-sample, re-treat, until salt drops below target.
7. Plug, photograph and hand over the numbersHoles plugged and colour-matched as far as the masonry allows. Course height, hole diameter, spacing, depth, method, pressure, product name, active content and certificate, and volume per linear metre all recorded, photographed and issued. Sample locations recorded precisely enough that nearby re-samples can be taken later to verify the outcome.

The Hydropoxy slab process, properly described

Our second treatment is for concrete slabs, and it works on a different principle to everything above. A slab is a single monolithic element sitting on the ground. There is no mortar bed, no course to cut and nothing to inject. Anyone offering to inject a slab against rising damp is describing something that does not exist.

Hydropoxy is an epoxy moisture barrier applied to the top of the slab, under new flooring. It is a negative-side treatment, which means it sits on the opposite face to the water. That is worth stating plainly: it manages the consequence — a floor covering that would otherwise debond, cup, blister or smell — on a slab that is going to keep receiving moisture from underneath. It does not stop the moisture arriving, it does nothing for the walls, and you cannot retrofit a membrane under an existing slab regardless of who tells you otherwise.

The order of operations matters as much here as it does on a wall.

1. Test the slab before anything elseIn-situ relative humidity probe testing to ASTM F2170, referenced by AS 1884:2021, in sleeved holes drilled to 40 per cent of slab thickness where the slab dries from one side, sealed and left to equilibrate before reading. Acceptance is commonly stated as not exceeding 75 per cent RH where no manufacturer's limit applies — and the flooring manufacturer's own limit may be stricter, in which case theirs governs the warranty. Surface tests and surface meters are far less reliable and have largely been superseded.
2. Establish where the water is coming from, and fix what can be fixedSlab moisture comes from a missing, torn or badly terminated under-slab membrane, from permeable or under-cured concrete, from ground water at the slab edge because the site does not drain, from landscaping added later that buried the slab edge, or from construction moisture in a young slab — in which case the answer is time, not a treatment. Drainage, falls and slab-edge exposure are corrected first, by a drainage or landscaping contractor. That work is frequently worth more than anything applied to the top of the slab.
3. Grind back to sound concreteDiamond grinding with on-tool dust extraction, removing old adhesives, coatings, curing compounds, laitance and any unsound or contaminated surface until sound concrete is exposed across the area. The barrier is only as good as what it is bonded to, and laitance is the most common reason a coating lifts.
4. Prepare the surfaceVacuum, then detail the work the grinder cannot do: cracks and joints treated, perimeters and penetrations detailed, and the surface profile checked against the product's requirement. Slab moisture is re-checked at this point, because grinding changes what the surface is doing.
5. Apply the epoxy moisture barrierApplied to the manufacturer's stated film build and within the stated recoat window, in the number of coats the system specifies for the measured slab condition, then left to cure before anything is placed on it. Film build and coat count are recorded and handed over.
6. Then the flooringInstalled by the flooring contractor to the flooring manufacturer's own moisture requirement, which is the requirement that governs their warranty. Installing an impermeable floor covering over a slab that has not been tested is the single most common cause of a new floor failing.

Silica, asbestos and lead — the regulated part of this work

Drilling mortar and grinding concrete both generate respirable crystalline silica. The Australian workplace exposure standard for respirable crystalline silica is 0.05 mg/m³ averaged over an eight-hour working day, and the controls are engineering controls first: on-tool dust extraction, water suppression where the method allows it, and respiratory protection as the last line rather than the first. Occupants are kept out of the immediate work area while drilling or grinding is in progress, and the work area is cleaned by vacuum rather than swept.

Asbestos and lead are the reason a pre-1990 building changes the shape of a job rather than just its price. Render, textured coatings, sheet linings, floor coverings and their adhesives in buildings of that era may contain asbestos, and identification before disturbance is a legal duty under the Work Health and Safety Regulation, with licensed removal where the material and quantity require it. Lead is present in paint on much of that stock, and abrasive or dry removal of it is the hazard. We do not remove render, plaster or flooring — that is a different trade — but drilling passes through whatever is on the face of the wall, so where the coating is suspect the work stops until it has been assessed. That is not a delay we negotiate.

Two more that belong on the same list. Subfloor soils in older buildings may have been treated with organochlorine termiticides, so subfloor inspection and any ground work there is done with advice rather than assumption. And on a heritage-listed or character-overlay property, council approval may be required before render removal, repointing or changes to external ground levels — which is a permission to obtain before the work is booked, not after it has started.

Then the wall dries, and that is measured in seasons

Cutting the source does not dry a wall. It stops the wall being resupplied. Everything already in the masonry then leaves by evaporation at whatever rate the wall, the room and the weather allow.

The working rule of thumb, from BRE Digest 163, is roughly one month of drying per 25 mm of wall thickness. A 230 mm solid or double-brick wall therefore takes the better part of a year. The Australian heritage guide reaches the same broad answer from the other direction: 3 to 6 months after replastering, or up to 12 months for wet thick walls. Both are order-of-magnitude expectations rather than specifications — the 25 mm rule was originally framed around drying construction moisture, not a salt-loaded wall recovering from decades of rising damp, and real drying is often slower in thick walls, poorly ventilated rooms and humid weather, which describes a good deal of South East Queensland.

Anyone promising a dry wall inside a week is describing the injection rather than the drying. The chemistry can be in the wall in a day or two. The water leaves on the wall's timetable.

Two things follow. Do not force it: increasing the drying rate increases the rate of salt crystallisation inside the masonry, and every crystallisation cycle does a little more damage, so steady moderate ventilation beats aggressive dehumidification and an air-conditioning outdoor unit blowing warm air at an old wall concentrates salt damage directly behind it. And do not judge acceptance on a meter: a salt-contaminated wall may never read dry, because hygroscopic salts hold atmospheric moisture indefinitely, which is why sign-off is judged on gravimetric free-water content from drilled samples taken near the recorded original locations.

What we hand over

The deliverable is a record somebody else can check, including somebody else you might later ask to check us. Sample locations are recorded precisely enough that a different consultant can take a nearby sample in five years and compare like with like.

• The full moisture profile: every sample, its height, its depth interval, its oven-dry moisture content and its hygroscopic moisture content at 75 per cent relative humidity, with free water shown as the subtraction rather than asserted.
• Salt species and percentage by weight where salt attack is suspected, stated against the 0.5 per cent concern threshold.
• Sample locations, recorded and photographed, so re-sampling nearby is possible later.
• External ground, paving and garden bed levels measured against the damp course rather than estimated by eye, with the position, type and condition of any existing damp course recorded.
• Weather and site conditions on the day of inspection, and dated photographs.
• The prerequisite schedule: what has to be corrected, by which trade, before any damp course is worth quoting, and the criteria for judging it corrected.
• For an injection: course height, hole diameter, spacing, depth, method, pressure, product name, active ingredient content and certificate, and volume of product used per linear metre.
• For a slab: the ASTM F2170 readings before treatment, the surface preparation carried out, and the film build applied.
• A monitoring plan with dates, and a clear separation of what is proven from what is inferred.
• The guarantee document, with its exclusions printed in full and in the same size type as the promise.

What we will not do

Two categories. The first is work that belongs to another trade, and we would rather name that trade than pretend the scope is ours. The second is methods we will not install at any price, with the reasoning attached rather than a slogan.

• Lowering ground levels, cutting back paving, removing garden beds and site drainage — landscaping, excavation and drainage contractors. This is frequently the highest-value money on the whole job and it is not ours.
• Gutters, downpipes, rainwater heads and flashings — roof plumber. Concealed leaks, condensate lines and irrigation — plumber.
• Subfloor ventilation to NCC Housing Provisions Part 6.2 — subfloor ventilation contractor. Wet-area waterproofing rectification to AS 3740:2021 — licensed waterproofer.
• Render and plaster removal, desalination poulticing, replastering in lime or lime-cement, and repointing in a weak lime mix — plasterers, repointing contractors and masonry conservators.
• Physical damp courses by slot sawing or undersetting, and undercutting at a slab or path junction — specialist masonry contractor. Undersetting also engages builder licensing and may require engineering certification.
• Passive electro-osmosis. It has no scientific basis: water moving through the porous medium is what creates the electrical potential, not the reverse, so earthing the resulting charge cannot prevent capillary rise. The heritage guide lists it among old treatments that should no longer be considered.
• Active electro-osmosis. The mechanism is real and is used industrially to dewater soils, but it has never been awarded a BBA Agrément certificate, BRE inspections found installed systems paired with a replastering system that may itself have been providing the barrier, the flow produced appears small relative to capillary flux and is further suppressed by salts, it must stay switched on permanently, and stray currents can corrode reinforcement and buried metal.
• Damp-proof paints, water-repellent surface sealers and hard cement render sold as the fix. They reduce evaporation, which raises the height of rise, and they trap salt at the coating interface where it crystallises and forces the coating off. The guide's instruction is not hedged: don't even think about sealing walls with water-repellent coatings.
• High-pressure injection above about 1000 kPa, which produces viscous fingering and untreated gaps, and can blow out weak mortar.
• A damp course quoted on meter readings alone, with no drilled samples, no hygroscopic moisture content, no salt analysis and no drainage assessment. If that is the evidence base, we would rather you spent the money on the assessment — from someone who is not us.

What it costs

Questions we actually get asked

Do you diagnose and quote on the same visit?

No, and that is deliberate. The site work is one visit, but the measurements that decide the scope are laboratory measurements: samples are oven-dried for total moisture content, then re-equilibrated at 75 per cent relative humidity for hygroscopic moisture content, and salt speciation runs alongside. That takes several days and the report follows the results rather than preceding them. What comes back first is a prerequisite schedule — the levels, drainage, gutters, plumbing and ventilation work that belongs to other trades — because in a meaningful share of cases that is the entire answer. A damp course is only quoted after those have been corrected and monitored, and the heritage guide's review period for that is at least twelve months.

You want to drill holes in my wall just to test it?

Yes, and it is the only method that produces evidence. Samples are taken from six to eight heights on a vertical line, at depths of roughly 0 to 10, 10 to 20 and 20 to 40 millimetres, taken past the last visible sign of damp. Mortar is sampled in preference to face brick or stone because it is far less disfiguring and easier to make good, unless the mortar is much less permeable than the units, in which case the salts have concentrated in the units and those have to be sampled instead. Drilling is done at slow speed with on-tool dust extraction, so heat does not drive moisture out of the sample before it is weighed. Holes are made good afterwards. The alternative — a surface reading from a two-pin meter — cannot distinguish a dry salty wall from a wet clean one, which is the exact distinction the whole scope turns on.

Twelve months of monitoring feels like a long time to sit on a problem.

It is, and the reason it is defensible is that this decay works on a scale of decades rather than weeks. Salt accumulates for a long time with very little visible damage while it fills the pore space, and there is no such thing as a damp emergency in a wall that has been doing this since the building went up. Twelve months of dated readings is what separates a genuine improvement from a dry spell, and a long drought looks exactly like a successful treatment. There is one genuine exception, and we will say so on the day rather than at the end of the year: mortar loss of around 50 millimetres across five to ten courses puts a wall at risk of local collapse, and that is structural work to be assessed now, not monitored.

If most of the work isn't yours, are you managing the other trades?

No. We write the prerequisite schedule, name what each item needs and which trade does it, and re-test afterwards. We do not head-contract the other trades, mark up their work or take a margin on it, and that is the arrangement that lets us write the schedule without an interest in how long it gets. It also means you are free to use trades you already know. What we will do is tell you what a correct outcome looks like for each item — the damp course sitting 150 to 250 mm above finished ground, a gravel strip of at least 300 mm, falls of about 50 mm over the first metre, subfloor ventilation to NCC Housing Provisions Part 6.2 — so the work can be checked against something written down.

What happens if the twelve months goes by and the wall is still wet?

Then the samples get taken again at the recorded locations and the same subtraction is run. If free capillary water is still present and still decreasing with height, the prerequisites are confirmed as corrected and the masonry is sound, that is the point at which a chemical damp course is the right answer, and it is quoted at $120 to $400 per linear metre depending on wall thickness, hole count and whether one face or both need treating. If free water has gone but hygroscopic moisture content is still high, the wall is salt-contaminated with no live source, the damp course is not the answer, and the work is desalination and replastering by a restoration trade at $80 to $250 per square metre. Both of those are real outcomes and we quote neither of them before the second round of testing.

Can the work be done entirely from outside?

Often, and that is the preference — we inject into the mortar bed on the external face, where the course can be set out at the correct height and the work causes least disruption. It depends on the wall. On a 230 mm one-brick wall the header course is drilled by preference precisely because it lets a single line of holes reach through the full thickness. Where a stretcher course has to be drilled instead, the stretchers on the internal side must also be treated, either from the internal face or by re-drilling through the same holes in a second phase, and internal treatment means plaster comes off and goes back — which is a plasterer's work at $40 to $120 per square metre to remove and $80 to $180 per square metre to reinstate. Whether your wall is one of those is determined before the quote, not discovered during the job.