The whole story

Every damp word, in plain English

Every term a homeowner meets in this subject, defined in plain English first and technical language second, with what each one changes about the decision in front of you.

Terms defined: 102, across seven tables
Australian height of rise: 1.0 - 1.5 m above ground, typical exterior limit
Active evaporative zone: 0.5 - 1.2 m; little evaporation below 0.3 m
Salt concern threshold: about 0.5% by weight of sample
The test that settles it: Hygroscopic moisture content, measured at 75% relative humidity
Damp course height (NCC): 150 mm above ground; 75 mm above paving that falls away; 50 mm where protected
Correct injection spacing: Holes 10 - 15 mm diameter at about 120 mm centres, to within 30 mm of the far face
Pre-1990 render or plaster removal: Asbestos and lead paint obligations apply before any of these words matter

Nobody arrives at this subject fluent in it. You arrive because there is a mark on a wall, and within a fortnight you are holding a document containing the words hygroscopic, crypto-florescence and gravimetric, usually handed to you by somebody who would like you to sign it.

So this is the whole vocabulary, laid out in the order the confusion tends to arrive. Plain English first, the technical term second, and then the part that actually matters: what the word changes about the decision in front of you.

One warning that applies to the entire list. Almost none of these words is a diagnosis. Efflorescence is not a diagnosis. A high meter reading is not a diagnosis. Salt damp is not a diagnosis. They are observations, and the distance between an observation and a diagnosis is a drill, a set of accurate scales and an oven.

Before you read any further, the honest shortcut: run the line-up and find out whether this is even rising damp. Most people who finish it are told they don't need us.

How to use this page

The tables below run from the physics outward: how water gets into a wall, what that looks like on the surface, what the salt does, which parts of the building the argument is usually about, how any of it gets measured, what the treatments actually do, and which documents the words come from.

Two conventions run through the whole list. Where a term has a plain-English name and a trade name, the plain-English one comes first, because that is the order a conversation should happen in. And where a term is routinely used to mean more than one thing, both meanings are given, because that ambiguity is where most of the money goes missing.

This page is not a substitute for testing. It is the thing that lets you read a report and a scope of works without having to trust the person who wrote them.

The word you would use, and the word on the quote

What you would call it	What it gets called	What it usually turns out to be
White stuff on my bricks	Efflorescence, or salt attack	Surface salt. Cosmetic on its own. The question is whether it keeps returning, which means water is still arriving and evaporating
A damp line across the wall	Tide mark	Usually a salt line rather than a water line, and a record of years of evaporation - which is why it survives long after the wall dried
The mortar has turned to sand	Fretting, or mortar erosion	Salt crystallising inside the pores just under the surface. Weak lime mortar sacrifices itself to protect the bricks around it
The render sounds hollow	Drummy render	Debonded render, usually with salt crystallised at the interface pushing it off
Paint keeps bubbling near the floor	Blistering, coating failure	Salt and moisture arriving at the coating interface. Repainting without removing the cause is a twelve-month fix at best
Black speckles in the corner	Black spot mould	Condensation, not rising damp. Archicentre puts about 70% of mould problems down to condensation and 30% to rising damp
Damp under the house	Subfloor moisture	In South East Queensland, usually ventilation, ground clearance, grading or a leak, not capillary rise
Wet patch on the concrete floor	Slab moisture, slab edge dampness	A membrane, drainage or concrete-quality problem. There is no capillary course in a slab to inject
Salt damp	Rising damp	The same underlying process. Salt damp is South Australian vocabulary that emphasises the salt; rising damp emphasises the water
The damp course has failed	Bridging, in most cases	An intact damp course with render, hard pointing, paving or a garden bed giving moisture a path around it

What people actually search for, and what it is called once a contractor is involved

How water gets into a wall, and how it leaves

Term	In plain English	Why it matters to you
Capillary action (capillary suction)	The force that pulls water into a narrow space against gravity, the same effect that makes a paper towel soak up a spill. The connected pores in brick, stone and mortar are the narrow spaces, and finer pores pull harder.	This is the entire mechanism of rising damp. It is standard, measured physics, not a fringe theory - and gravity barely resists it. Including gravitational drainage in the published model reduces calculated heights by only about 2 to 5%.
Rising damp	Groundwater drawn up into a wall through those pores.	It needs three things at once: liquid water at the base, a continuous absorbent path upward, and a face where water can evaporate. Remove any one and it stops - which is why the cheapest fixes are usually at the base of the wall and not in it.
Salt damp	The same process, named for its consequence rather than its cause. South Australian vocabulary.	If you are reading Adelaide advice in Queensland, the physics carries but the emphasis does not. Adelaide is the national worst case because hot drying summers meet very salty soils.
Sorptivity	A measured property describing how fast a material sucks water up by capillary action.	One of the three things that set how high damp climbs in a given wall. It is also why old walls behave differently from new ones: mortar becomes more sorptive over decades of water passing through it.
Evaporation rate	How fast water leaves the wall face as vapour.	The most misunderstood variable in the subject. Reduce it - by rendering, painting or sealing - and the damp climbs higher to find more surface to evaporate from. This is why sealing a wall makes it worse, not better.
Steady height of rise (equilibrium height)	The level where the damp settles, at which water arriving from below exactly equals water evaporating away.	It rises in direct proportion to how absorbent the material is, with the square root of wall thickness, and falls with the square root of evaporation rate. Typically 1.0 to 1.5 m in Australia. Doubling wall thickness from 150 to 300 mm moves the modelled height only from 0.61 m to 0.87 m.
Porosity	How much of a material is empty space.	Brick and soft stone are porous; granite, slate and dense concrete are not. Higher porosity generally means less durable, and many small pores are worse than a few large ones.
Permeability	How well those pores are connected, and therefore how easily water and air travel through.	This is what people mean when they say a wall breathes. Any coating that stops it breathing shortens the wall's life, because moisture and salt then have nowhere to go but into the masonry.
Solute (osmotic) suction	An extra pull created once the salt concentration in the wall exceeds that in the soil below, drawing yet more water upward.	It is why an old salty wall is a fundamentally worse case than a young clean one with identical geometry. Salt pulls harder and evaporates slower, so the problem partly sustains itself.
Time lag	How long a wall takes to reach its new steady state after something changes.	About 31 days in the standard modelled example, but inversely proportional to evaporation rate - so years behind a coating. A newly raised garden bed can take one to three years to show, and a treatment judged successful at three months has proved nothing.
Falling damp	Water entering from above - failed roofing, blocked or leaking gutters and downpipes, failed flashings - and percolating down.	The tell is damp that is worst high on the wall. Salt appears where water evaporates, which may be well away from where it got in, so it has to be traced deliberately.
Penetrating damp	Water coming in sideways through a leaking pipe, failed shower waterproofing, defective mortar joints or driven rain.	Failed wet-area waterproofing is routinely read as rising damp because it presents at the base of the wall in the room next to the bathroom. That is a licensed waterproofer's job, running $3,000 to $15,000 per wet area.
Lateral damp	Penetrating damp specifically from higher ground on the other side of a wall - retaining walls, cut-and-fill sites, garages, basements, split levels.	The diagnostic signature is a wall that is wetter above the damp course than below it. Chemical injection cannot resist water under pressure; this is a drainage and tanking problem.
Condensation	Water coming out of the air onto a cold surface, rather than in through the wall.	By a wide margin the most common misdiagnosis. Worst in winter, worst overnight, on cold external corners and behind furniture, affecting the tops of walls as often as the bottoms, and showing black spot mould rather than salt bloom.
Interstitial condensation	The same thing happening inside the wall rather than on its face.	As a wall warms it exhales air from its pores and as it cools it inhales. If that air is humid and the masonry drops below dew point, water condenses inside. Hygroscopic salts then hold onto it.
Dew point	The temperature at which the air in a room becomes saturated and starts depositing water on any surface colder than that.	This is the number that settles the condensation question. Log room temperature and humidity plus wall surface temperature for a week. If the surface repeatedly falls below the room's dew point, it is condensation, and no damp course changes that.

Mechanism terms

What it looks like on the wall

Term	In plain English	Why it matters to you
Tide mark	The horizontal stain line near the top of the damp zone.	Usually a salt line rather than a water line, deposited where evaporation has been happening for years. It often sits slightly below the true damp front and persists long after the wall has dried, so it is a history, not a live reading.
Evaporative zone	The band of wall where most evaporation actually happens.	In Australia typically 0.5 to 1.2 m above ground, with very little below 0.3 m because the air near the ground is more humid and moves more slowly. This is also where the salt damage concentrates.
Efflorescence	The white powdery or fluffy bloom on the surface, formed when evaporation happens at the wall face and salt crystallises harmlessly in open air.	Cosmetic on its own, and normal on new brickwork for a year or two. The diagnostic question is not whether it is there, but whether it keeps coming back after cleaning - which means a live source.
Sub-florescence (crypto-florescence)	The same salt crystallising inside the pores instead of on the surface, because the evaporation front sits within the wall.	This is the destructive version and the single most important distinction on the page. Crystallisation pressure is enough to disrupt the strongest masonry. A wall with no visible salt can be in worse condition than one covered in it, because rain washes the evidence away.
Fretting	Grain-by-grain crumbling of a masonry surface, caused by salt crystallising in the pores just beneath it.	Mortar fretting is usually the first sign, because weak lime mortar sacrifices itself to protect the bricks around it. Loss of about 50 mm across five to ten courses puts you at risk of local collapse, which is a now problem rather than a next-year problem.
Spalling	Surface material breaking away in flakes or plates rather than grain by grain.	In brick and stone it is usually salt or freeze-thaw. In concrete it is most often corroding reinforcement expanding and pushing the cover off - commonly called concrete cancer - which is a different problem with a different repair, and not rising damp at all.
Drummy	Sounding hollow when tapped, because render, plaster or tiling has debonded from what is behind it.	Drummy render below the damp course is one of the signature signs of slab edge dampness. Drummy render on a wall with a damp problem usually has salt crystallised at the interface, which is what pushed it off.
Fireskin	The harder, denser outer surface a brick develops in the kiln.	Once salt attack pops that skin off in flakes, the softer body underneath decays much faster. Losing the fireskin is a step change in the decay rate, not a cosmetic event.
Case hardening	A naturally toughened outer surface on some sandstones.	Sealing such a stone with a water-repellent coating traps salt behind the hardened layer and delaminates it, exposing stone that can be surprisingly weak. It is the clearest example of a coating causing the damage it was sold to prevent.
Blistering (paint bubbling)	Paint lifting off in bubbles, typically low on the wall.	Salt and moisture arriving at the coating interface. Repainting without removing the cause and allowing the wall to dry makes recurrence close to guaranteed - drying after replastering takes 3 to 6 months, up to 12 on thick walls.
Black spot mould	Dark speckled growth, usually in corners, behind furniture and on window reveals.	A condensation signature, not a salt signature. The accepted control threshold is keeping surface relative humidity below about 80% over month-long periods, which is a ventilation and heating question rather than a masonry one.
Lime run (limescale)	A hard white crust, often streaked, from lime leaching out of cementitious material above.	Frequently mistaken for efflorescence. It indicates water moving through fresh concrete or mortar above, which is a plumbing or falling-damp clue. Calcium carbonate is relatively insoluble and is not a salt-attack problem in itself.

Symptom terms

The salts, and why they are the actual problem

Term	In plain English	Why it matters to you
Soluble salts	Salts that dissolve in water and travel into the wall with it. Water evaporates; salt cannot, so it stays and accumulates.	A 150 mm wall moves roughly 0.88 litres per day per metre of length, about 320 litres a year. Ten metres of affected wall transports on the order of 3,000 litres a year, and every litre leaves its salt behind. The wall is a salt delivery mechanism, not just a wet object.
Hygroscopic	Describes salts that pull water vapour straight out of the air.	This is why a wall with a perfect damp course and no leak can still read wet forever. It is also why a wall feels damp in humid weather and dry in dry weather, with no liquid source anywhere.
Deliquescent	A stronger version of the same thing: the salt absorbs so much moisture that it dissolves into liquid, then re-crystallises when the air dries.	Every wet-dry cycle enlarges the pores slightly, so the next cycle does a little more damage. Cyclic wetting and drying is the key driver of salt-attack decay, and frequency matters as much as severity.
Critical (deliquescence) relative humidity	The humidity above which a particular salt starts pulling water out of the air.	It varies by salt, which is why two walls in the same weather behave differently. Crucially, mixtures go wet at a lower humidity than either salt alone - so real walls, which always contain mixtures, are worse than single-salt figures suggest.
Chloride	Common salt and its relatives. From saline groundwater and soils, sea spray, airborne salt from inland salt lakes, and acid cleaning of brickwork.	Sodium chloride goes wet at about 75% relative humidity, which in Australia is an ordinary week. Magnesium chloride goes wet at about 33% and calcium chloride at about 29 to 32% - below which almost no occupied Australian building ever sits. A wall carrying those is permanently in the wet phase and will read damp on any instrument, forever, with no water source at all.
Nitrate	Salts of nitric acid. From leaking sewers and septic systems, animal urine, garden fertiliser washed into the wall, and bird droppings.	The most diagnostically useful salt on the list. A nitrate-heavy result means stop and find the source - a leaking sewer, an over-fertilised garden bed, or a building that was once a stable. Calcium nitrate deliquesces at roughly 47 to 55%, which is why some walls never dry.
Sulfate	Salts of sulfuric acid. From groundwater, Portland cement, sulfate-bearing clay and air pollution.	Sodium sulfate is described in the Australian guide as particularly damaging, because it swaps between an anhydrous form and a ten-water hydrate that occupies far more space. It is the prime suspect where sound bricks are splitting and delaminating rather than merely fretting at the surface.
Magnesium sulfate (Epsom salts)	A sulfate formed where sulfates react with magnesium-bearing material such as dolomite.	Where analysis returns mostly magnesium sulfate, look for a contaminated material rather than groundwater - bedding sand, aggregate or dolomitic stone. Fixing the wall without removing the contaminated sand simply restarts the clock.
Gypsum (calcium sulfate)	Only slightly soluble, and the main constituent of common modern plaster.	This is the direct practical rule for replastering: never use gypsum plaster where dampness may continue, because gypsum is itself a slightly soluble salt and residual moisture triggers salt attack inside the new plaster. Lime or lime-cement instead.
Calcium carbonate	Limestone, marble, and the cured lime in traditional mortars. Relatively insoluble.	Generally benign as a damaging salt, which is fortunate given how much Australian building stock is made of it. Where it appears as a hard crust it is usually lime leaching from above, which is a water-movement clue rather than salt attack.
Salt mixtures	What real walls actually contain: whatever groundwater, cement, fertiliser, sea spray, sewage and cleaning chemicals have delivered over a century.	Do not reason from a single textbook deliquescence figure to a prediction about your wall. Knowing the mixture is what tells you the humidity range over which the wall is actively cycling, and therefore how aggressive the decay will be.
The 0.5% threshold	The working rule of thumb: more than about 0.5% salt by weight of sample is cause for concern.	This single number should appear in any competent report on a salt-affected wall, and it is what drives the decision on whether desalination belongs in the scope. Its absence from a quote is worth asking about.

Salt chemistry terms

The parts of the building the argument is usually about

Term	In plain English	Why it matters to you
Damp-proof course (DPC)	A waterproof layer built into the base of a wall above ground level, to block moisture rising from the ground. Modern ones are usually 0.5 mm embossed black polyethylene.	Many nineteenth-century Australian buildings never had one. Acceptable materials are listed in AS/NZS 2904, and the code requires it not less than 150 mm above adjacent ground, 75 mm above paving that slopes away, or 50 mm where a carport or verandah protects it.
Bridging	Anything that gives moisture a path around an otherwise perfectly good damp course - render carried down over it, a garden bed or path built up above it, a concrete floor abutting it, or hard pointing across it.	This is one of the most common genuine causes of damp in houses that already have a damp course, and it is one of the cheapest to fix. Injecting a second damp course above a sound bridged one changes nothing at all.
Bed joint (mortar bed)	The horizontal mortar joint between courses of brick.	This is where a chemical damp course is injected, because mortar generally diffuses better than brick. It is also where a physical damp course is sawn in.
Header course / stretcher course	A header shows the short end of the brick; a stretcher shows the long side.	On a 230 mm one-brick wall the header course should be drilled by preference, because it runs the full thickness. Where only a stretcher course is drilled, the stretchers on the other side must also be treated - otherwise you have half a barrier that looks identical from the street.
Cavity wall	Two leaves of masonry with an air gap between them, tied together and drained to the outside.	The cavity is a drainage design, not just an air gap. Mortar droppings on the ties or at the cavity base defeat it, which produces damp patches often higher than the damp course - a bridged cavity, not rising damp.
Brick veneer	A single leaf of brick as a weather skin over a timber or steel frame.	Common in post-war Australian housing. Damp behaviour is dominated by the cavity, the flashings and the slab edge rather than by capillary rise through a solid wall.
Weephole	The deliberate gap left open in the vertical joints at the base of a cavity or above a flashing, so water inside the cavity can escape.	Blocked, rendered-over or painted-shut weepholes trap water in the cavity. Clearing them is minutes of work and regularly ends an argument that had a five-figure quote attached to it.
Cavity flashing	A membrane inside the cavity that catches water and directs it out through the weepholes.	Missing, torn or badly terminated flashing is a standard borescope finding. It converts a presumed rising damp case into a diagnosed bridged cavity in about ten minutes.
Render	A cement, lime or cement-lime coating applied to masonry.	The critical property is breathability, not hardness. Hard cement render on a damp wall reduces evaporation, which raises the height of rise, and traps salt at the interface which then pushes the render off. It also conceals the very pattern a diagnosis depends on.
Plasterboard	Gypsum sheet lining on the inside of a wall. Called drywall in American writing.	Gypsum is calcium sulfate, a slightly soluble salt, so it is the wrong material anywhere dampness may continue. Foil-backed board also produces false high readings on a pin meter.
Subfloor	The space under a suspended timber floor.	In South East Queensland's high-set timber stock this is where most real moisture problems live. The code sets minimum aggregate ventilation openings by climate zone, ground clearance of typically 150 mm - 400 mm where termite inspection access is required - and openings within about 600 mm of corners.
Ag line (agricultural drain)	A perforated pipe wrapped in geofabric, laid in free-draining gravel, that collects groundwater and carries it to a legal discharge point.	The standard answer where ground on one side is higher than the floor on the other. Site drainage works run $1,500 to $12,000 and are frequently the highest-value dollar spent on a damp job.
Sterile zone	A clear strip of coarse gravel, at least 300 mm and preferably over 500 mm wide, kept between the wall and any garden bed.	Gravel stops rain splashing up the wall while still letting soil moisture evaporate to the sky instead of through your masonry. Keep drippers at least 500 mm off the wall and grade the first metre to fall about 50 mm away.
Slab-on-ground	A concrete floor slab cast directly on the ground, usually with thickened edge beams.	A slab is a single monolithic element, not a coursed wall. There is no mortar joint to inject and no course to cut, which is why a masonry damp course is not a treatment for a slab under any circumstances.
Vapour barrier / under-slab damp-proofing membrane	The 0.2 mm plastic sheet laid under a slab to stop ground moisture rising into it.	It must underlie the whole slab, extend under edge beams to ground level, be lapped at least 200 mm and be sealed at penetrations. It cannot be retrofitted once the slab is poured. South Australia and New South Wales vary the code to require high impact resistance rather than medium, a direct response to salt damp in saline soils.
Slab edge dampness	Moisture soaking into the exposed edge of a slab or footing and migrating inward.	The signature set is persistent damp on the slab edge, efflorescence and drummy render below the damp course, damp carpet edges, musty odours, tile bond failure near external walls and rust staining. Very often it follows landscaping done years after the house was built.

Construction terms

Testing: what each method proves, and what it cannot

Term	In plain English	Why it matters to you
Relative humidity (RH)	How much water vapour the air is holding as a percentage of the most it could hold at that temperature.	Almost every threshold in this subject is an RH figure: 75% for the hygroscopic test and for common salt going wet, about 80% at a surface for mould control, 75% inside a slab for flooring acceptance. The number is meaningless without the temperature and the location it was taken at.
Electrical resistance (pin) moisture meter	The two-pin gadget almost everybody uses. It measures electrical conductivity between two pins.	It is calibrated for timber. Soluble salts are electrolytes, so a dry but salty wall conducts as well as or better than a wet clean one, and the meter cannot tell them apart. Readings above 100% moisture content are common on salty walls - a physically impossible figure that leaves no room for the masonry itself. Useful for mapping and monitoring the same wall over time. Useless as proof.
Capacitance / search-mode meter	A non-invasive pad meter that senses relative moisture variation just under the surface.	Genuinely useful for finding anomalies without damaging a heritage finish. Depth of read is shallow and poorly defined, typically 10 to 30 mm, and it gives no absolute moisture content. Screening only.
Gravimetric moisture content	The reference test. Samples are drilled at known heights and depths, sealed immediately, weighed wet, oven-dried and reweighed. The weight lost is the water.	Unlike a surface meter it measures water rather than conductivity. Slow-speed drilling matters, because drill heat drives moisture off before you can weigh it. This is what BS 6576 means when it requires masonry samples.
Moisture profile	A vertical series of six to eight samples up a wall, taken past the last visible sign of damp, usually at depth intervals of 0-10, 10-20 and 20-40 mm.	It is the shape of the gradient, decreasing with height, that is the actual evidence for rising damp. One reading at skirting height proves nothing, and a wall wet from the inside and a wall wet from the outside look identical at the surface.
Carbide (Speedy) test	An on-site test: a weighed drilled sample is sealed with calcium carbide, the water reacts to produce gas, and the pressure rise reads as moisture content.	Far better than a pin meter and immune to the salt-conductivity artefact. But it measures total moisture only, so it still cannot tell salt-held water from water rising from the ground.
Hygroscopic moisture content (HMC)	A laboratory measurement of how much water your wall sample will hold from the air alone, because of its salt. Oven-dried samples are equilibrated at 75% relative humidity and reweighed.	The one test that settles the argument, and almost nobody does it. Subtract it from total moisture and what is left is free water actively rising. High HMC with negligible free water means a salt-contaminated wall with no live source - which needs desalination, not a damp course.
Free (capillary) moisture	Water in the wall that came from a live liquid source, as opposed to water the salt harvested from the air.	Its presence, and whether it decreases as you go up the wall, is the actual evidence for rising damp. It is also the correct basis for signing a job off, because a salt-loaded wall may never read dry on any meter.
Salt speciation	Laboratory identification of which salts are present and in what quantity, by ion chromatography and ICP-AES.	The species points at the source. Nitrate points at sewage, fertiliser or a former animal use. Chloride points at groundwater, sea spray or acid cleaning. Magnesium sulfate points at contaminated aggregate. Alkali sulfates point at cement.
Total dissolved solids (TDS)	A cheaper proxy: crush a weighed sample, dissolve it in a known volume of deionised water, measure conductivity and convert to a percentage.	Combined with sulfate and nitrate test strips it gives enough to manage most projects and to verify that desalination is working, by resampling nearby locations later. It gives a total salt load, not a species breakdown.
Thermal imaging	A camera that maps surface temperature. Damp areas often read cool because evaporation cools them.	It does not measure moisture; it measures temperature and moisture is inferred. It produces false positives from voids, insulation gaps and recent sun, and false negatives where there is no evaporative cooling to see. Every thermal finding must be confirmed by an actual moisture measurement.
Data logger	A device left in place recording air temperature, humidity and surface temperature continuously.	The only reliable way to confirm or exclude condensation, which is the most common misdiagnosis in the subject. A week including cold nights is the minimum; a fortnight to a month is realistic.
Borescope	A small camera on a flexible probe, pushed through a drilled hole into a cavity or subfloor.	Direct visual evidence of mortar snots on wall ties, bridged cavity bases, missing flashing, blocked weepholes, buried damp courses and standing water. It regularly converts a presumed rising damp case into a diagnosed bridged cavity in about ten minutes.
ASTM F2170	The in-situ relative humidity probe test for concrete slabs: sleeved holes drilled to a set depth, usually 40% of slab thickness, sealed and left to equilibrate before reading.	The correct tool for slab moisture questions and the normative method referenced by AS 1884:2021, with acceptance commonly stated at 75% RH unless the flooring manufacturer sets a stricter limit. It tells you the slab is wet; it does not tell you why.

Measurement terms. This is the section worth reading twice.

Treatments, and what each one actually does

Term	In plain English	Why it matters to you
Chemical damp-proof course (injection)	Drilling holes along a mortar joint and introducing a silicone-based cream or fluid that lines the pores and makes them water-repellent.	It does not block the wall - the masonry still breathes and dries. Correct practice is 10 to 15 mm holes at about 120 mm centres, drilled to within about 30 mm of the far face. It is now the most common remedial method in Australia and it is one of the two things we do.
Silane / siloxane	The active silicone chemistry in those creams and fluids.	Active-ingredient content varies from around 15% up to around 80% between certified products, and weak formulations have still obtained certification. The product certificate matters far more than the word silane appearing anywhere.
Cream	A high-solids water-based emulsion delivered by cartridge gun to the back of the drilled hole, which then diffuses through the pore structure.	Preferred where solvents are a problem: fire risk, fumes, or polystyrene cavity insulation that a solvent would dissolve. Should not be attempted where the mortar or masonry is weak and crumbling.
Solvent-borne fluid (gravity feed or low pressure)	Siloxane carried in an organic solvent, either fed from bottles over about 24 hours or injected at low pressure.	Longer track record than cream. Solvents can dissolve tar or bitumen from an existing damp course and spread brown staining through the masonry, so an old tar-and-sand damp course must never be drilled and impregnated directly.
Viscous fingering	What goes wrong when injection pressure is too high: the fluid races ahead in fingers and leaves untreated gaps between them.	This is why low pressure is correct and high pressure is a defect rather than a feature. Injection above about 1000 kPa risks blowing out weak mortar and producing a barrier with holes in it that nobody can ever inspect.
Slot sawing	Sawing a horizontal slot along a mortar joint in short sections, sliding in a polyethylene damp course and repacking the joint tight.	A genuine physical barrier, and the most certain form where it can be done. Only possible in regularly coursed masonry with reasonably soft mortar - not random rubble, and dense bluestone and granite blunt the blades. Not work we perform.
Undersetting	Removing short sections of the base of a wall down to the footing, one at a time, and rebuilding each on a new damp course.	The best treatment for very severe salt damp, because it is the only method that removes salt-laden masonry and installs a barrier in one operation. Expensive and skilled, $700 to $1,500-plus per linear metre. Not the same as underpinning, which fixes footings. Not work we perform.
Undercutting	Cutting through a concrete floor, path or hearth where it bridges the damp course at the wall junction.	Sound where a specific concrete element is demonstrably bridging an otherwise intact damp course. Has structural implications where the slab is load-bearing, and must be paired with vertical damp-proofing at the junction or the bridge simply re-forms.
Desalination poultice	Drawing salt back out of a wall using absorbent clay or paper-pulp poultices, captive-head washing and vacuuming, so salt crystallises in the poultice rather than in your bricks.	The step whose absence is why decay continues above a technically successful damp course. It runs $80 to $250 per square metre, it is iterative, and it is the line item most often missing from a cheap quote. Not work we perform.
Sacrificial mortar or render	A deliberately weak, porous lime-based mix used at the base of a wall so salt crystallises in it rather than in the masonry.	It is meant to decay - you renew it periodically, and that is the point rather than a defect. Weak lime mortars protect the surrounding masonry precisely by failing instead of it.
Repointing	Raking out failed mortar joints and refilling them.	The rule is weak lime, not hard cement. Hard cement repointing drives the damp further up the wall and can damage the bricks. And there is a trap on the other side: extensive repointing after treatment can re-bridge a chemical damp course, so the treated zone may need re-treatment once the new mortar has cured.
Limewash	A traditional lime-based finish, far more breathable than modern paint.	On a wall that is damp, drying or carrying residual salt, breathability is the single most important property a coating can have. The ladder runs limewash, then cement-based paints, then acrylics, with oil-based alkyd paints worst and unsuitable on any wall still drying.
Gypsum plaster	Ordinary modern plaster, chemically calcium sulfate.	Never use it where dampness may continue. It is itself a slightly soluble salt, so residual moisture triggers salt attack inside the new plaster, which is why so many freshly plastered walls fail within a year. Lime or lime-cement instead.
Tanking	Fully waterproofing a below-ground structure to hold back water under pressure, usually with a drained cavity system, a sump and a pump.	A completely different engineering problem from a damp course. Chemical injection prevents capillary rise but cannot resist a hydrostatic head, so it is the wrong tool for a basement or a retained wall. Runs $400 to $1,200 per square metre. Not work we perform.
Negative-side treatment	Waterproofing applied to the dry face - the side away from the water - rather than the wet face.	The usual case in an occupied building, because nobody wants to excavate. An epoxy moisture barrier applied to the top of an internal slab is a negative-side treatment: the water is still under the slab, and the barrier stops it reaching the flooring.
Positive-side treatment	Waterproofing applied to the face the water actually arrives at, which is the technically preferable position.	On a slab that means the under-slab membrane, laid before the pour and impossible to retrofit. On a retaining wall it means excavating and tanking the retained face. This is why prevention detailing during construction matters so much.
Epoxy moisture barrier (slab)	Grinding an internal concrete slab back to sound clean concrete and applying an epoxy film that new flooring can be laid over.	It is flooring preparation, not a cure for the ground moisture underneath. It manages the symptom so an adhesive and a floor covering do not fail. It is the second of the two things we do, and it does nothing whatsoever about drainage, levels or a missing membrane.
Electro-osmosis	Using electricity to influence water movement in a wall.	The passive version, an earthed copper strip, has no scientific basis - water movement creates the electrical potential rather than the other way round - and the Australian guide lists it among old treatments that should no longer be considered. The active version applies a DC current, uses a real industrial mechanism, has never earned a BBA certificate, must stay switched on permanently, and its performance in salty walls is openly described as unclear.

Remediation terms

Where these words come from

Reference	What it is	What it governs here
NCC	The National Construction Code, formerly the Building Code of Australia.	Sets the performance requirements for resisting moisture from outside and moisture rising from the ground. Adoption is jurisdiction-specific: as at August 2026 the operative edition in Queensland and New South Wales is still NCC 2022. Confirm the adopted edition for your project.
ABCB Housing Provisions 5.7	Weatherproofing of masonry.	Lists acceptable damp course materials and sets the position: not less than 150 mm above adjacent ground, 75 mm above paving that slopes away, 50 mm where a carport or verandah protects it, and as low as 15 mm in low rainfall intensity areas.
ABCB Housing Provisions 6.2	Subfloor ventilation.	Minimum aggregate ventilation openings by climate zone, of the order of 2,000, 4,000 and 6,000 mm2 per metre of wall for zones A, B and C without a ground membrane, roughly halved where an impervious membrane is laid. Also ground clearance, debris removal, grading and no dead air spaces.
AS 2870	Residential slabs and footings.	Site classification by soil reactivity, from Class A to Class P, the under-slab membrane specification, and the requirement for a minimum fall of 50 mm over the first metre away from the building.
AS 3700	Masonry structures.	Design and construction of masonry, including detailing of damp courses, flashings, cavities, weepholes and durability in salt and marine exposure.
AS/NZS 2904	Damp-proof courses and flashings.	The material specification for sheet membrane, strip and collar damp courses. It explicitly does not cover vapour barriers or mortar-type damp courses.
AS 3740:2021	Waterproofing of domestic wet areas.	The standard governing showers and bathrooms - which is to say, the standard governing the failed-shower cases so often misdiagnosed as rising damp.
AS 4654.1 and 4654.2	Waterproofing membranes for external above-ground use.	Balconies, roofs, podiums and planters. Relevant to damp diagnosis mainly as an exclusion: a failed balcony or planter membrane above can present as damp at the base of the wall below.
AS 1884:2021	Floor coverings: resilient sheet and tiles, installation practices.	Makes the in-situ relative humidity probe test the normative method for assessing slab moisture before laying moisture-sensitive flooring. Acceptance is commonly stated at 75% RH, and the manufacturer's own limit may be stricter and governs the warranty.
AS 4349.0	Inspection of buildings, general requirements.	The framework a damp investigation can appropriately be commissioned under, as an inspection of particular technical aspects. Note that AS 4349.1, which most pre-purchase building inspections are done under, is not a damp investigation.
BS 6576	British code of practice for diagnosis of rising damp and installation of chemical damp courses.	Not Australian, but the reference procedural standard cited in the Australian guide's own list. Its central requirement is that masonry samples must be taken - rising damp cannot be diagnosed from surface measurements.
BRE Digest 245	Rising damp in walls: diagnosis and treatment.	The methodological reference for the vertical sample profile and for determining both total moisture content and hygroscopic moisture content, so free capillary water can be separated from salt-held moisture.
RICS / Historic England / PCA Joint Position Statement, September 2022	Investigation of moisture and its effects on traditional buildings.	Not a standard, but the most authoritative current consensus. Its two central principles: traditional solid-walled buildings do not perform like modern ones, and observing moisture in an old building should not automatically be treated as a defect requiring a fix. The damp-proofing industry's own trade body co-signed it.
Salt attack and rising damp, David Young OAM, 2008	Jointly published by the Heritage Council of NSW, Heritage Victoria, the South Australian Department for Environment and Heritage and Adelaide City Council.	The definitive Australian technical guide, free to download, and the source of most of the working numbers on this page: the seven key steps, the 0.5% salt threshold, the 1.0 to 1.5 m height range, the caution on moisture meters and the instruction not to insert any damp course until the basic housekeeping has been done and monitored for at least a year.

The documents behind the terminology

Words with no technical meaning at all

The last group is not terminology. These are words that appear in this market, carry no defined meaning, and cannot be tested against anything. They are listed here because recognising them is worth as much as knowing what sorptivity is.

We apply this list to ourselves first. None of these words appears anywhere on this site describing our own work, and if you find one, it is a mistake and we would like to know.

Permanent. A correctly installed chemical damp course forms a continuous water-repellent zone that capillary moisture cannot climb past. It does nothing about salt already in the wall above it, which keeps cycling in and out of solution. There is no defensible way to describe that as permanent.
Cure, eliminate, guaranteed dry. A salt-contaminated wall may never read dry on a meter, because hygroscopic salts hold atmospheric moisture indefinitely. Acceptance has to be judged on drilled-sample free water, which is a measurement, not an adjective.
Any moisture reading above 100%. It is physically impossible - it leaves no room for the masonry itself - and it is common on salty walls. A number like that is evidence about the instrument, not about the wall.
Damp-proof paint, waterproof coating, sealer, on a wall with rising damp. Sealing the face reduces evaporation, and the steady height of rise scales inversely with the square root of evaporation rate, so the damp front climbs. In the modelled example it takes about 425 days to reappear above the render, which is precisely why the treatment looks successful before it fails.
Structural rising damp. Not a term in any standard on this page. Damp can eventually become a structural problem through mortar loss, but the phrase is used to attach urgency, not meaning.
Free inspection. Free is a commercial term, not a technical one. The useful question is who absorbs the cost of a visit that ends in you not needing anything.
Salt attack, used on its own as a diagnosis. It is a real and correct term - it is the title of the national guide - but it names a decay mechanism, not a cause. The cause is whatever is delivering the water.
A guarantee described only by its length. Twenty, twenty-seven and thirty year guarantees are advertised in this category as badge images. The term is the least informative part of the document. Ask for the exclusions, in writing, before you ask about the years.
Rising damp is a myth. It is not. The mechanism is published, quantified and reproduces observed heights from Britain to a 4 m thick church wall in Rome showing 5.3 m of rise. What is true is that it is over-diagnosed, which is an entirely different claim and the one worth arguing about.

Questions we actually get asked

Is salt damp the same thing as rising damp?: Yes, in the sense that matters. They describe the same physical process with different emphasis: rising damp names the water, salt damp names what the water leaves behind. Salt damp is South Australian vocabulary, and it took hold there because Adelaide is the national worst case - hot drying summers driving high evaporation, meeting very salty soils. The physics carries to Queensland unchanged. The emphasis does not. In humid subtropical South East Queensland, high ambient humidity 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.
If I only remember one term from this page, which should it be?: Hygroscopic moisture content. Everything else on this page describes the problem; that one test decides what you should pay for. Oven-dried samples from your wall are equilibrated at 75% relative humidity and reweighed, which measures the water the salt alone will hold from the air. Subtract it from total moisture content and what remains is free water actively rising from the ground. High salt-held moisture with negligible free water means a wall that needs salt removed, not a damp course installed. The Australian heritage guide states that this is the only method that will distinguish moisture due to rising damp from moisture due to hygroscopic salts.
My inspection report says efflorescence. Is that a diagnosis?: No, it is an observation, and a fairly weak one on its own. Efflorescence is salt that has been carried into masonry by water and deposited on the surface as the water evaporated. On new brickwork it is normal, harmless and fades within a year or two. On old brickwork the diagnostic question is whether it returns after cleaning, because recurrence means water is still arriving and evaporating - which is a live source that has to be found. There is also a worse case the word conceals entirely: where evaporation happens inside the wall instead of on its face, salt crystallises within the pores and there may be no visible bloom at all. A wall with no visible salt can be in worse condition than one covered in it.
Why does the inspector keep tapping the wall with a knuckle?: To find drummy areas - render, plaster or tiling that has debonded from what is behind it and now sounds hollow. It is one of the few genuinely useful tests that costs nothing and cannot lie. Drummy render on a damp wall usually has salt crystallised at the interface, which is what pushed it off. Drummy render below the damp course on a slab-on-ground house is one of the signature signs of slab edge dampness. It does not tell you why the wall is wet, but it reliably tells you where the coating has already given up, and that is where sampling should happen.
What is the difference between a vapour barrier and a damp-proof course?: Position and job. A damp-proof course is a horizontal barrier built into a wall, above ground level, to block moisture rising through masonry, and AS/NZS 2904 covers acceptable materials. A vapour barrier or under-slab damp-proofing membrane is the 0.2 mm plastic sheet laid under a concrete slab before the pour, lapped at least 200 mm, sealed at penetrations and extended under the edge beams to ground level. The important practical difference is that a damp course can be retrofitted into a wall and an under-slab membrane cannot be retrofitted at all once the slab exists. Anyone offering to install one under your existing house deserves scrutiny.
Which of these words should actually appear in a quote?: A defensible scope names numbers, not categories. For injection that means the product and its active-ingredient content, hole diameter of 10 to 15 mm, spacing of about 120 mm, depth to within about 30 mm of the far face, whether the header course or both faces are treated on a 230 mm wall, the fluid volume per linear metre as a figure, and gravity feed or low pressure rather than anything above about 1000 kPa. It should also name what happens to the salt - desalination where analysis exceeds about 0.5% by weight - and specify a drying period of 3 to 6 months, up to 12 on thick walls, before finishing. If none of those numbers appear, a different contractor could not build the same barrier from the document, which means it is a heading with a price under it.
Why does so much writing on this subject not apply in Australia?: Because most of it is British, and the climate is the variable that drives the whole system. Hotter, drier conditions push far more litres per year through the same wall, and Australian soils are genuinely saline, so each litre delivers more salt. The national guide describes the result as much higher rates of decay in this country than in the UK, to the point where younger Australian buildings can be in worse condition than far older northern European ones. That cuts both ways in the argument. The British over-diagnosis critique is largely correct and worth taking seriously. The British conclusion that it is essentially all condensation does not transfer, and importing it wholesale into an Australian context is its own diagnostic error.

Worth reading

Most people who send us photos don't end up needing us

That isn't false modesty, it's the numbers. Damp gets blamed on rising damp far more often than it is rising damp. Send three photos and we'll tell you which one you've got — including when the answer costs you a Saturday and a shovel rather than a contractor.

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Mon–Fri 07:00–17:00. No free inspection by a bloke on commission, no thermal camera if you sign tonight, and nothing in red capitals.