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 the waterproofer's work either.

Which is also why this is an ordinary Gold Coast problem rather than an exotic one. Coastal South East Queensland hands a wall all four factors at once: water tables sitting close to the surface across the low-lying canal and reclaimed estates, saline groundwater and salt-laden air driving chloride into masonry, subtropical rain that arrives faster than the ground can take it, and a large stock of older brickwork where paving, paths, soil and garden beds have been built up over the decades until the damp course is buried or bridged. Rising damp here is common. It is not a rare misdiagnosis, and pretending otherwise to sound clever helps nobody. The useful question on a local wall is almost never whether it is damp — you can see that — but which of the causes is actually running, because one of them is a damp course and another one is a downpipe.

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 actually gets looked at 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 not only after rain, because rain washes surface salt away and hides the evidence.

That structured looking is what the site visit is, and it is a diagnosis rather than a preamble to one. Ground and paving levels read against the damp course. Gutters, downpipes and the fall away from the building traced to where the water actually goes. Salt banding, and where it sits relative to the top of the damp. The height and shape of the damp line, and whether it runs the whole base of the wall or stops obediently under a downpipe. A moisture meter used where it helps — as one input, not as the argument.

The table below is the whole hierarchy of methods, top to bottom, because it is worth knowing what exists. The first rows are site work. The rows below them are laboratory work, they belong to a commissioned forensic investigation rather than to a normal remedial job, and the next section sets out the short list of situations where paying for one is the right call.

Separating salt-held water from free water — and when it is worth commissioning

Two walls can look much the same and need entirely different work. One still has water arriving at the base of it. The other was cured years ago, kept the salt, and the salt has been pulling moisture out of the air ever since. On site that fork is read from the evidence in front of you — whether there is a live water source at the base of the wall, whether the damp moves with the weather and the season, what the ground and the gutters are doing, whether the salt band sits where a still-active wall would put it. On most houses that reading is clear enough to act on.

Where it is not clear, or where the answer has to convince somebody who was never there, there is a laboratory method that settles it by subtraction, and this is what it involves. 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 strongest evidence there is for rising damp.

Two results, two entirely different scopes. Free water present and decreasing with height means a live source, and once the prerequisites have been corrected, 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 — and on this coast chloride is close to background. 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.

None of that is part of a normal job, and nothing here sells it. It earns its keep in a short list of situations: a building dispute, an insurance claim, an expert-witness matter, a pre-purchase decision somebody intends to argue about, or a wall where competent people have looked at the same evidence and reached different conclusions. If you are in one of those, what you want is an investigator with no rectification work sitting behind the findings — an investigation-only consultancy are a waterproofing consultancy and forensics practice who investigate and do not carry out remedial work, which is exactly the separation a dispute needs. It is paid, independent work, it is nothing to do with this site, and it is not what a normal rising damp job requires. If you are not in one of those situations, the money is better spent on the drainage.

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

What comes out of a competent visit is not a quote for a damp course. It is what is actually feeding the wall, and what has to be corrected, in what order, and by which trade, before a damp course is worth discussing. Step six does not get sold on the same visit as step two, and a licensed waterproofer does not perform the prerequisite work themselves — which is the arrangement that lets that list be honest about how long it is.

The list is drawn from the same short set 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 — which in a subtropical downpour move more water in ten minutes than the rest of the year's drainage problems combined. 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 gets a proper run of weather before anybody talks about step six again. That is the heritage guide's own instruction rather than a stalling tactic — housekeeping first, effectiveness assessed over at least a year — and the reason is that seasons move the readings. Storms, floods, drought and a humid summer all change what a wall is doing, and a long dry spell looks exactly like a successful treatment. Plenty of these jobs end at this stage, with the damp gone and no masonry work done at all. When that happens the masonry line on the invoice stays at zero, and that is a result rather than a lost sale.

Then, and only then, the damp course — and what to ask about it

If the wall is still being fed once the prerequisites have been corrected and it has had enough weather to prove it, 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 belongs to the waterproofer: they inject the course, and it is the only wall treatment in their scope.

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 is one you are entitled to ask about before the work starts, of whoever is doing it. A method nobody outside the van can check is not much of 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. DrillThe installer drills holes 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, and on-tool dust extraction.
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 used is worth comparing against the manufacturer's stated rate per linear metre, and that comparison is a fair thing to ask about. 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 is heavy enough to matter — the usual threshold quoted is 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 a licensed waterproofer, and it runs $80 to $250 per square metre and is iterative: poultice, let it draw, repeat until the salt stops coming back.
7. Plug and make goodHoles plugged and colour-matched as far as the masonry allows. The figures worth asking about at this point — of any installer — are course height, hole diameter, spacing, depth, method, pressure, product name, active ingredient content and certificate, and the volume of product used per linear metre against the manufacturer's stated rate.

The Hydropoxy slab process, properly described

The second of a licensed waterproofer's two treatments 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 for this particular question 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 what the system's performance actually depends on, so they are worth asking about.
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. A licensed waterproofer does 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 they 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 between November and March.

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 the outcome on a meter reading: a salt-contaminated wall may never read dry, because hygroscopic salts hold atmospheric moisture indefinitely. The honest test of whether it worked is whether the wall is still being resupplied — the ground, the drainage, the height and behaviour of the damp line through a wet season, and whether salt comes back through new plaster. Where somebody needs that judgement to be defensible to a third party, gravimetric free water from drilled samples is what provides it, and that is investigation work rather than part of the job.

What a full investigation contains — and what to ask for on a normal job

Two very different documents get called a damp report, and it is worth knowing which one you are being handed. The first is a forensic investigation: commissioned, paid for, laboratory-backed, and built so that somebody other than its author can check it — so that a different consultant could take a nearby sample in five years and compare like with like. The list below is what that document contains, and it is the standard to hold one to if you have paid for one or been given one in a dispute.

The second is what comes out of a site visit: what is wrong, what is causing it, what has to be corrected and by which trade. That is not a watered-down version of the first. It is a different job, and on the overwhelming majority of houses it is the one that gets the wall fixed. The list is here so you can tell the two apart, and so you know what is fair to ask for on either.

• 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.
• On any job, paid investigation or no-charge visit alike: what has to be corrected, by which trade, before a damp course is worth quoting — and what a correct outcome looks like for each item, so it can be checked against something written down.
• For an injection, ask whoever installs it: 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, ask whoever coats it: the ASTM F2170 readings before treatment, the surface preparation carried out, and the film build applied.
• A clear separation of what has been proven from what has been inferred, and a plain statement of what would change the answer.
• The guarantee document, with its exclusions printed in full and in the same size type as the promise — ask for it before you sign, not after.

What a licensed waterproofer will not do

Two categories. The first is work that belongs to another trade, and it is better to name that trade than to pretend the scope covers it. The second is methods a licensed waterproofer 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 the waterproofer's.
• 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.
• Forensic investigation for a dispute, an insurer or an expert-witness matter. A contractor who does the remedial work is the wrong person to produce evidence about whether it is needed. That is a consultancy's job — an investigation-only consultancy do it, and they carry out no rectification.
• 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 sold off a meter reading alone, without anybody having looked at the ground levels, the paving, the garden beds, the downpipes or where the water goes when it rains. The meter is not the problem — competent contractors carry one and use it. The problem is that no meter can tell you where the water is coming from, and on this coast that is the part that decides whether you need an injection or a length of downpipe extension.

What it costs

Questions that actually get asked

Is a damp inspection actually free, or is there a fee at the end of it?

It normally carries no charge, and there is nothing to buy at the end of it. A competent inspection looks at the wall inside and out, looks at the ground levels, the paving, the garden beds, the gutters and where water goes when it rains, read the pattern, height and shape of the damp and any salt banding, get under the house or into the cavity where that is possible, and use a moisture meter where it helps. What you get back is what is causing the damp and what has to be corrected — including the items that are not their work and that they earn nothing from. There is no inspection fee, no report to purchase and no laboratory analysis on the menu, because none of those is a thing a damp contractor sells.

Does someone need to drill my wall to diagnose this?

Usually not. A wall tells an experienced inspector a great deal without being drilled: where the ground sits relative to the damp course, where the roof water lands and where it goes, the height and shape of the damp line, whether a salt band sits at the top of it, whether the damp runs the full base of the wall or stops obediently under a downpipe, and whether it moves with the season. Read together with the drainage and the ground levels, that is a diagnosis, and on the great majority of Gold Coast houses it is the one that gets acted on. Drilled samples answer a narrower question — how much of the moisture is free water and how much is salt holding humidity out of the air — and that question is worth paying to answer when the stakes are legal rather than practical: a dispute, an insurer, an expert-witness matter, or a purchase somebody intends to argue about.

The heritage guide says a year before a damp course. Do I really have to wait that long?

That is the guide's instruction for doing it properly, and the reasoning is sound: 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. What the year actually buys you is seasons. A wet summer and a dry winter both tell you something a single visit cannot, and a long dry spell looks exactly like a successful treatment. In practice most people correct the drainage and the ground levels first and watch what the wall does through a proper wet season, which is the same idea on a Queensland calendar. There is one genuine exception, and it gets said 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 watched.

Isn't rising damp supposed to be rare?

Much of the material telling you it is a myth comes out of a UK argument about solid-wall Victorian housing, and it does not travel especially well to a subtropical coast. Here the conditions that produce it are ordinary: water tables sitting close to the surface across the low-lying canal and reclaimed estates, saline groundwater and salt-laden air, rain that arrives faster than the ground can absorb it, and decades of ground level creeping upward — new paving, a new path, a garden bed, another 100 mm of turf underlay — until the damp course is buried or bridged. Rising damp on the Gold Coast is common. What is also true is that a good share of it is being fed by something a plumber or a landscaper can fix in a day, which is why the order of the seven steps matters more here than almost anywhere, and why these pages give condensation, a leak and efflorescence the same billing as capillary rise.

If most of the work isn't theirs, does the waterproofer manage the other trades?

No. A good scope names what each item needs and which trade does it, and will come back and look at the wall afterwards. They do not head-contract the other trades, mark up their work or take a margin on it, and that is the arrangement that lets the list be written without an interest in how long it gets. It also means you are free to use trades you already know. What does get stated is 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 rather than against a feeling.

What if the drainage and levels are corrected and the wall is still damp?

Then you are in the smaller group where a chemical damp course is genuinely the answer, and that is quoted at $120 to $400 per linear metre depending on wall thickness, hole count and whether one face or both need treating. The other real outcome is a wall where the source is gone but the salt stayed: no free water arriving, but enough hygroscopic salt in the masonry to keep the surface damp and the paint failing. That wall does not need a damp course at all — it needs desalination and replastering by a restoration trade, at $80 to $250 per square metre. Telling those two apart is usually possible on site from the history and the behaviour of the wall. Where it genuinely is not, that is one of the few cases where paying for laboratory analysis is the sensible move rather than guessing at four figures.

Can the work be done entirely from outside?

Often, and that is the preference — a licensed waterproofer injects 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 worked out before the quote, not discovered during the job.