Should you do this yourself?

There is no consumer kit market in Australia, and that changes the question

Before you decide whether you have the skill, check whether you can assemble the kit. What is actually on a hardware shelf in Australia is make-good material, not injection material: rapid-set hydraulic plugging cement, gun-grade polyurethane sealant in a cartridge, polymer-modified patching mortar, bitumen paint. Every one of those sits on the surface. None of them travels into a crack under pressure and none of them fills the wall thickness.

What the method actually requires is a different category of equipment. The workhorse is a 13 mm mechanical packer with a non-return valve, seated in a 13 mm hole drilled at 45 degrees to the face. Behind it is a single-component injection pump, commonly rated to 200 bar and worked in the 35 to 140 bar band for polyurethane leak sealing through mechanical packers. For comparison, low-pressure epoxy through glued surface ports runs at roughly 0.7 to 3.5 bar, which is 10 to 50 psi. A caulking gun is not on that scale at all.

Then there is the chemistry you have to control rather than just apply. Hydrophobic polyurethane is dialled in on site with an accelerator dosed at roughly 1 to 10 per cent by volume, which sets gel times anywhere from about 20 seconds to several minutes. Too fast and it sets in the hose. Too slow on a running leak and it washes out before it gels. That dose is a judgement made from the flow rate in front of you, and it is the sort of judgement that is learned by getting it wrong on someone else's building.

Where doing it yourself is genuinely fine

A dry hairline crack in a garden wall is not a waterproofing job. It is a cosmetic one, and you should feel free to fill it on a Saturday with a tube from the hardware store and think no more about it.

The conditions below all have to be true at once. If even one of them is not, skip to the next section, because the honest answer changes.

On crack width, it helps to know what the design standard expects. AS 3600, the Australian concrete structures standard, carries serviceability crack width limits broadly in the range of 0.1 to 0.4 mm depending on the type of element and its exposure classification. In plain terms, fine cracking in concrete is normal and designed for. The question is never simply whether a crack exists. It is whether water is coming through it and whether it is still getting wider.

If you are unsure whether it is still moving, that is also a genuinely do-it-yourself job. A tell-tale, which is a simple two-part gauge glued across the crack with a scale printed on it, costs very little and tells you the truth. Read it over 4 to 12 weeks so it spans a temperature and moisture cycle. If it has not moved, you have a dormant crack. If it has, you have a different problem and no filler of any kind is the answer.

• The wall is free-standing or above ground, with nothing behind it holding back soil or water.
• There is no head of water anywhere against it. No retained soil, no garden bed above, no slab draining toward it.
• The crack is dry and stays dry, including during and after rain.
• The crack is dormant, or you have confirmed it with a tell-tale over 4 to 12 weeks.
• Nothing habitable, valuable or electrical is on the other side.
• There is no rust staining along the crack line, no hollow-sounding concrete beside it, and no flaking.
• The wall is not part of a retaining structure, a tank, a pool, a car park deck or anything a body corporate owns.
• You are filling it because it looks untidy, not because you are trying to stop water.

Where it makes the problem worse, and dearer

There are four situations where a do-it-yourself attempt does not simply fail. It actively raises the cost and difficulty of the repair that follows it.

Anything under head. Once there is a column of water or saturated soil pushing against the other face, you are working against hydrostatic pressure, and pressure is the whole problem. Surface-applied material has nothing to grip and gets pushed off. Worse, sealing one path when the water has nowhere else to go simply moves the leak: seal a crack and you can start a new one three metres away, because water tracks laterally between the membrane and the concrete and exits at whatever is now the weakest point. That is not a failure of your workmanship. It is physics, and it happens to professionals too, which is why we put it in writing before we start.

Anything you would surface-port. Glued-on surface ports with a bead of stiff filler capping the crack are the low-cost method, and they have a legitimate narrow use in dry, low-pressure structural epoxy work on sections too thin to drill. On an actively leaking wall they are a well-known way to waste a day. The surface seal will not adhere to wet concrete. It blows off, usually at the least convenient moment, and it takes a layer of paint or render with it.

Anything below ground or on the negative side. Sealing from the dry side is a legitimate technique, but it is the technique with the least margin for error, because the seal has to be keyed into the body of the wall rather than sitting on its face. That is why the professional method drills at 45 degrees, offset from the crack line by roughly half the element thickness so the hole intersects the crack at mid-depth, to between two-thirds and three-quarters of the wall thickness and never through. A seal keyed inside the wall is pressed in by the water. A seal on the face is pushed off by it.

Anything structural, moving, post-tensioned or corroding. Diagonal cracks, cracks that widen toward the top, cracks with any lean, bulge or step in them, and cracking that follows the line of the reinforcement with rust staining are all signals that sealing is the wrong move. Rust staining in particular means the steel inside is expanding as it corrodes; filling the crack seals the problem in while it keeps growing.

Isocyanate: the honest reason not to

Polyurethane injection resins are built on MDI, a methylene diphenyl diisocyanate prepolymer. Isocyanates are respiratory sensitisers. In plain language, they can trigger an immune response in your airways that behaves like occupational asthma, and once you are sensitised you are sensitised for good.

The Safe Work Australia workplace exposure standard for isocyanates is 0.02 mg per cubic metre as an eight-hour time-weighted average, with a short-term exposure limit of 0.07 mg per cubic metre over 15 minutes. Those are low numbers. The part that matters more is that a person who has already been sensitised can react well below the standard, which means the exposure standard protects the unsensitised, not the sensitised. There is no treatment that reverses it. There is only avoidance.

This is the reason a licensed crew wears an air-supplied or correctly fit-tested cartridge respirator rather than a dust mask, keeps a current safety data sheet on site for every product, ventilates enclosed spaces, wears chemical-resistant gloves and eye protection, carries spill and decontamination provisions, and is placed on health monitoring where exposure is ongoing. It is a controlled occupational exposure with a regime around it, not a smell you put up with.

Two things worth knowing so this is not read as scaremongering. First, once the resin has reacted and cured, which happens within minutes, it is an inert plastic and it is not hazardous. The risk is entirely in the handling of the uncured product. Second, a fit test is a real procedure with real equipment, and a respirator that has not been fit-tested to your face is doing considerably less than you think it is. That is not something you can arrange for a single afternoon of work.

The trade-off is worth stating plainly. A homeowner sealing one crack has a small exposure, taken once. But it is taken without extraction, usually in a confined room, usually without a fit-tested respirator, and the consequence if it goes wrong is permanent and affects the rest of your life rather than the rest of the job. We do not think that is a good trade, and we would give the same answer if we sold nothing.

Silica, and why an enclosed garage is the worst place in the house to drill

The second hazard is one people take far less seriously than isocyanate, and it kills more tradespeople. Drilling concrete generates respirable crystalline silica. Australia's workplace exposure standard is 0.05 mg per cubic metre as an eight-hour time-weighted average. It causes permanent, progressive lung disease, and there is no version of it that gets better.

It is worth understanding the quantity involved, because "a bit of dust" undersells it. A properly set out injection uses 13 mm holes at 150 to 400 mm centres, alternating either side of the crack, which works out to roughly three to seven holes per linear metre. In a 200 to 250 mm thick wall, each hole is drilled to between two-thirds and three-quarters of the thickness, so 130 to 190 mm deep. Take a modest 3 metre crack in a garage wall: call it 15 holes at 150 mm deep. That is about 2.25 metres of 13 mm drilling, which converts roughly 0.3 litres of solid concrete into airborne dust, or something in the order of 700 grams of material. That is arithmetic from the stated dimensions, not a measurement, but the order of magnitude is the point.

Now consider where that happens. An enclosed garage or undercroft is the worst room you could pick. It is small, the ceiling is low, the roller door is usually shut because you are working, and there is no cross-ventilation. Dust does not disperse in a space like that. It hangs, and then it settles, and then you re-suspend it every time you move. The same problem makes basements and lift pits the highest-risk spaces on our own sites, and it is exactly why the controls there are not optional.

The controls that work are on-tool dust extraction or wet drilling, plus respiratory protection. A household vacuum held near the hole is not dust extraction; it passes the fine fraction straight through the bag and back into the room, which makes the situation worse rather than better. If you are going to drill concrete indoors at all, hire the extraction with the drill, and open everything you can open.

What a failed attempt costs you afterwards

The money argument is not the main one, but it is real, and it usually runs the opposite way to how people expect.

A complete professional repair of a single basement or garage wall crack, including attendance, exposing the crack, injection, cutting the packers back and basic making good, sits in an indicative range of $900 to $2,500. Underneath that, an honest site attendance minimum in metropolitan south east Queensland during business hours is around $450 to $900 plus GST, because someone has to travel, set up a pump, work and make good. A diagnostic investigation with moisture readings, crack monitors, water testing and a written report is $450 to $1,500 if you want the cause established rather than guessed.

Here is what a failed attempt does to those numbers. The professional method includes water-flushing through each packer before injecting, which does three jobs at once: it clears laitance, dust, efflorescence and calcite out of the crack, it pre-wets a dry crack so the resin has water to react with, and, critically, it proves the crack is hydraulically connected from one packer to the next. If water does not appear at the next packer, the set-out is wrong and we find out before we inject rather than after.

A crack whose mouth is packed with cured sealant, epoxy filler or hydraulic plug fails that test in a way that tells us nothing. We cannot distinguish "the crack does not connect" from "your filler is in the way". That means the mouth has to be raked or ground out first, and on a crack that has been surface-sealed along its length that is a genuine additional operation before the job starts.

There is a diagnostic cost too, and it is often the larger one. Surface-sealing a crack does not stop the water; it diverts it. By the time you call someone, the water is emerging somewhere else, and the story you can tell about where it appears no longer matches where it enters. You have removed the best evidence in the building.

One more thing to be clear about, since it is specific to Queensland. Trade work valued over $3,300 including labour, materials and GST requires the appropriate QBCC contractor licence, and residential work over that threshold performed by a licensed contractor also carries QBCC home warranty insurance obligations. Work you do yourself carries no statutory warranty and no home warranty cover, because there is no contract and no licensee. If it fails, the cost of the second attempt is entirely yours.

The do-it-yourself that actually works: everything upstream of the crack

If you want to spend a Saturday improving your leak, do not spend it on the crack. Spend it on the water.

Blocked or absent subsoil drainage, blocked weep holes, missing falls, downpipes discharging at the footing, and surface water running toward the building are the actual cause behind a very large share of enquiries that arrive asking for injection. This is not a way of talking people out of work. It is the single most useful thing a specialist can say, and it is the first thing we check on site before quoting anything.

The reason it matters more than the crack is mechanical. Sealing the face of a wall without restoring the drainage behind it raises the water head against that wall. On a retaining structure that also raises the load on a wall that may never have been designed for saturated backfill. So the sequence matters: drainage first, sealing second.

Everything on the list below is genuinely homeowner work, costs almost nothing, and occasionally turns out to be the entire fix.

• Clear the weep holes. Render, garden beds, mulch and paint routinely block them. Clearing them sometimes stops the leak on its own.
• Find the ag line outlet and check that water actually comes out of it during rain. A subsoil drain that has been crushed, silted or root-blocked is doing nothing.
• Extend any downpipe that discharges within a metre of the footing, and check the stormwater pit is not full of leaves.
• Look at the fall on the driveway, path or paving beside the wall. If water runs toward the building, that is the problem, and re-grading is cheaper and more permanent than any repair we could sell you.
• Check the planter box or garden bed above for a blocked outlet. A planter with a blocked outlet is a bathtub, and sealing it makes it a heavier one.
• Watch it during rain, not after. Twenty minutes standing in the wet with an umbrella will tell you more than any amount of looking at a dry stain.
• If the damp is constant and has no relationship to rain at all, run the 48-hour plastic sheet test before you spend anything, because you may be looking at condensation rather than a leak.

If you are going to do it anyway

People do this regardless of advice, and a page that pretends otherwise is not much use. So here is the harm-minimisation version, in order.

1. Photograph it before you touch itWide shot, then close, with a tape or a coin in frame for scale, and date the files. Photograph it dry and again during rain. If it turns into an insurance claim, a builder's defect claim or a body corporate matter, this is the only evidence that will still exist after you have filled it.
2. Rule out the things that are not the crackDrainage, a leaking service, condensation, surface water. Pressure-testing a suspect service line is quick to arrange and expensive to get wrong. Injecting a wall above a leaking main is a plumbing job with a resin bill attached.
3. Do not attempt anything under headIf there is retained soil, a garden bed, a slab or a water table on the other side, stop. Nothing you can buy will hold against pressure applied to the face of the wall.
4. Do not surface-port a wet wallThe stiff surface seal that ports rely on will not adhere to damp concrete. It will blow off, and it will take the coating with it.
5. Get the space ventilated before you open anythingRoller door up, windows open, cross-flow if you can create it. This applies to both the resin and the drilling. An enclosed garage with the door down is the worst case for both hazards at once.
6. Hire the dust extraction with the drillOn-tool extraction or wet drilling, every hole. Not a household vacuum. This is the control that actually reduces respirable crystalline silica exposure rather than moving it around the room.
7. Wear real respiratory protection and read the safety data sheetA disposable dust mask is not isocyanate protection. Every product you use has a safety data sheet and you are entitled to it from the supplier before you buy. Read the exposure and first-aid sections, not just the storage advice.
8. Never seal the only way outBefore you close a path, ask where the water will go instead. If the answer is nowhere, you are about to build hydrostatic pressure into a cavity, a planter box or an under-slab void. That is a design problem, and sealing it makes it a structural one.

When it cannot wait

There is one situation where the do-it-yourself question is the wrong question entirely: water is running into the building now, and every hour matters. In that case the priority is not repair quality, it is damage control, and there are four things to do in the next hour.

Isolate power to anything in the affected area, at the board, before you go anywhere near standing water. Move vehicles out of the path of the water and out from under any ceiling that is dripping. Photograph and video everything before you start moving belongings, because that footage is worth more to an insurer than any description you can write afterwards. And do not let anyone chase the flow along the wall with a bucket of quick-set. Filling in front of moving water traps it, moves the exit point, and destroys the evidence of where it entered.

What actually kills active flow is a fast-gelled hydrophobic polyurethane, dosed for a gel time near the short end of the 20-second range, and often a hydraulic cement plug or oakum packing installed first to reduce the flow enough that the resin gels where it is put rather than washing down the wall. That is a same-day intervention, and then the methodical work follows once the flow has stopped.

We do not run a 24-hour badge, because a badge that generates unanswered calls at 2am is worse than no badge. In business hours, ring us and a person answers. Outside them, send photographs and we call first thing.

Questions we actually get asked

Can I buy polyurethane injection resin in Australia as a homeowner?

Realistically, no. Injection resins are sold through trade counters to contractors, and Australia has no equivalent of the American consumer kit market. Even the Australian distributors that rank on the search term for polyurethane crack injection are business-to-business suppliers, and the one whose consumer collection page we checked returned zero products. If you do find a supplier willing to sell to you, ask for the safety data sheet before you buy and read the isocyanate section. That document, not the sales advice, is the thing that should decide it.

Can I hire an injection pump the way I would hire a concrete saw?

General hire fleets stock concrete and construction plant, not injection equipment. A single-component polyurethane pump is a specialist item, commonly rated to 200 bar and normally run in the 35 to 140 bar band, and it needs to be flushed and maintained properly between jobs or it seizes with cured resin inside it. It is not in the hire catalogue for the same reason a resin supplier will not sell to you: the equipment on its own does not make the job safe or successful.

I already filled the crack and it still leaks. Have I made things worse?

Usually the honest answer is a bit, but recoverably. Two things happen. The filler in the crack mouth interferes with the water-flush test we use to prove the crack connects from one packer to the next, so it has to be raked or ground out before we can set out properly, which is an extra operation. And surface-sealing does not stop the water, it diverts it, so the place it now appears may be metres from where it enters. That second one costs more than the first, because it degrades the diagnosis. Bring us the photographs you took before you filled it, if you have them.

There is a fine dry crack in my garden wall. Do I need to do anything at all?

Probably not. Fine cracking in concrete is normal and designed for: AS 3600, the Australian concrete structures standard, carries serviceability crack width limits broadly in the range of 0.1 to 0.4 mm depending on the element and its exposure. A dormant hairline crack in a dry, free-standing wall with nothing behind it is a cosmetic question. Fill it if it bothers you. If you want certainty about whether it is still moving, glue a tell-tale across it and read it over 4 to 12 weeks so it spans a temperature and moisture cycle.

If I do it myself and it fails, is anything covered?

No. In Queensland, trade work valued over $3,300 including labour, materials and GST requires the appropriate QBCC contractor licence, and residential work over that threshold done by a licensed contractor also brings home warranty insurance obligations with it. Work you carry out on your own property has no contract, no licensee and therefore no statutory warranty and no home warranty cover. Nor does a hardware-store product warranty extend to a use the manufacturer never described. The second attempt is entirely at your cost.

What respirator would I actually need if I did this myself?

An air-supplied respirator, or a cartridge respirator with the correct cartridge for isocyanates that has been fit-tested to your face. The fit test is the part people skip and it is the part that decides whether the equipment works, because a seal that leaks at the cheek is not filtering anything. Add chemical-resistant gloves and eye protection, ventilate the space, and keep the safety data sheet on hand. Once the resin has cured, within minutes, it is inert; the entire risk lives in the uncured product, and it is a risk you cannot take back.

Is the drilling really that big a deal for one small job?

It is bigger than it looks in an enclosed space. Australia's workplace exposure standard for respirable crystalline silica is 0.05 mg per cubic metre over eight hours, and the resulting lung damage is permanent. A modest 3 metre crack needs roughly 15 holes at 13 mm, each 130 to 190 mm deep in a typical wall, which converts something in the order of 700 grams of concrete into airborne dust. In a closed garage with a low ceiling and the roller door down, that dust does not go anywhere. If you drill at all, hire on-tool extraction or drill wet, and open the space up.

Where to next

• when it can't wait
• how concrete crack injection actually works
• fifteen times injection is the wrong fix
• run the leak diagnostic before you spend anything
• price your job by linear metre
• the 48-hour condensation self-test