Water coming through your garage wall

The four things that cause this in South East Queensland

Nearly every wet garage wall between Brisbane and the Gold Coast falls into one of the patterns below. The tell-tale column is what separates them, and checking it costs nothing.

Timing matters more than anything else you can observe. Water that arrives during the downpour is coming over the ground. Water that arrives hours or days after the rain has stopped is coming through the ground, and that is the pattern that responds to injection.

Before you pay anyone to quote: check the ag line and the weep holes

An ag line, short for agricultural drain, is the perforated pipe sitting in gravel behind a retaining wall or alongside a footing. Its job is to collect groundwater and carry it away to a legal discharge point. A weep hole is a small deliberate gap left in a wall so trapped water can escape. Both are invisible when they work and both fail silently.

Find where the ag line is supposed to come out. It is usually a 90 mm or 100 mm pipe end at a garden bed, a kerb, a pit or a downpipe connection at the low side of the property. During or straight after heavy rain, water should be running out of it. If nothing comes out while the garage wall is wet, the drain is blocked, crushed, full of silt or was never connected — and that is the leak, not the concrete.

Then look at the wall itself from the outside. Weep holes rendered over, painted over, or buried under a raised garden bed are one of the most common causes in this housing stock, and they are also one of the cheapest to fix. Check where the downpipes discharge as well. A downpipe emptying at the footing puts thousands of litres straight into the ground beside a garage in a single storm.

None of this needs a contractor. It needs twenty minutes and a wet afternoon — and where DIY is fine and where it backfires marks the line. If clearing the drain fixes it, several thousand dollars have just been saved — and finding that out from a web page beats finding it out from the second contractor.

The wet patch is usually not where the water gets in

Water entering a below-ground wall does not travel in a straight line. It runs sideways between the outside waterproofing membrane and the concrete, or between a structural slab and the topping poured over it, and it comes out wherever the concrete is weakest. On a lot of jobs the visible crack is simply the exit, and the entry is a construction joint several metres away.

This is why the joint at the bottom of the wall matters so much. It is called the kicker joint, and it is the line where a wall was poured onto an already-set slab. The two pours never fully bond, so it is a continuous path along the entire base of the wall. On a leaking under-house garage it is very often the real entry point even when a crack higher up the wall is what you can see and what you point at.

Practically, that means the diagnosis is worth more than the injection. What matters is where the water arrives, when it arrives relative to the rain, what the ground does behind the wall, whether there is a topping slab, and whether there is any chance of a leaking pipe. A weeping wall above a leaking water main or a broken stormwater line is a plumber's job, and it takes ten minutes to rule out and a fortune to get wrong.

What injecting a garage wall actually involves

1. Work out the path before the drill comes outDriveway fall, downpipe discharge, weep holes, ag line outlet, and whether the water arrives during or after the rain. If it arrives during, the surface water is the fix and injection should not be quoted at all.
2. Expose the wallPaint, render and plasterboard hide how far a crack really goes, and you cannot inject what you cannot see. On a lined or rendered garage, stripping back is quoted as its own item. It is a real cost and burying it in a rate is how a quote turns into a variation later.
3. Drill beside the crack, not into it13 mm holes at 45 degrees, alternating one side then the other, offset from the crack line by roughly half the wall thickness — about 125 mm on a 250 mm wall — so each hole meets the crack at mid-depth. The holes go two-thirds to three-quarters of the way through and never out the far side, because breaking through loses all the pressure. Drilling concrete produces silica dust, which has an Australian workplace exposure limit of 0.05 mg per cubic metre, so on-tool extraction is not optional. In a closed garage that matters more, not less.
4. Fit mechanical packersA packer is the small steel or plastic fitting that connects an injection hose to the hole. A mechanical packer locks into the concrete when a nut is tightened, sealing inside the wall so resin goes through the crack rather than onto it. Packers glued to the surface will not stick to a wall that is actively leaking, which is why a cheap quote so often fails inside one wet season.
5. Flush with clean waterWater pumped through each packer proves the crack is connected from one fitting to the next, washes out the salt deposits and dust that would otherwise block resin, and wets a dry crack so the resin has something to react with. If water does not appear at the next packer, the set-out is wrong and it has to be changed before anything is injected.
6. Inject from the bottom upAlways the lowest packer first. Resin pushes the water up and out of the crack instead of trapping it, the base seals first so the fill builds upward off a sealed foundation, and resin appearing at the next packer is direct proof it has travelled. A gushing point gets killed first with a fast-setting resin so it does not wash the rest of the work away.
7. Cut back the next day and make goodPackers stay in the wall for at least 24 hours. The shafts are then cut off 10 to 20 mm below the surface, the recesses filled with a non-shrink patching mortar and ground flush. Re-rendering and repainting is quoted separately, because it is a separate trade's worth of work and pretending it is included is how people end up disappointed.

When injection is the wrong answer for a garage

Experienced contractors turn this work down regularly, and these are the reasons why. Where any of them describe the situation, injection will either do nothing or make the problem more expensive.

• Surface water off the driveway. If the water arrives while it is raining and comes across the floor rather than through the wall, the fix is drainage and levels — a grate, a hump, a re-graded apron or a redirected downpipe. Cheaper, more reliable and permanent.
• A blocked or missing subsoil drain. Clear it, or install one. Sealing the wall with the drain still blocked raises the water pressure against it.
• Rust stains and flaking concrete along the crack line. That is reinforcing steel corroding inside the concrete and pushing it apart. Sealing the crack traps the problem and the steel keeps expanding. The correct repair is concrete repair — breaking out to sound concrete, treating the steel and reinstating.
• A tide mark up to about a metre with white salt bloom and perished plaster on a masonry wall. That is rising damp — groundwater climbing through the brickwork by capillary action. It is treated with a chemical damp-proof course, a silane or siloxane cream injected into the mortar joints, which is a completely different product doing a completely different job.
• Damp that has no relationship to rain, on a cold surface, in a closed-up garage with poor ventilation. That is usually condensation. The fix is ventilation and reducing moisture sources, and injection achieves nothing except a bill.
• A crack that is still moving. Diagonal cracks, cracks that widen toward the top, and any lean, bulge or step in the wall are engineer territory — how to read width, pattern and movement sets out how to tell them apart. Crack monitors should be fitted and read over 4 to 12 weeks before anyone injects anything, because a rigid repair in a moving crack simply cracks again beside itself.

What it costs, and what moves the number

A single crack in an accessible garage wall, injected properly and made good, sits at roughly $900 to $2,500 plus GST. That covers attendance, exposing the crack, drilling and packers, injection, the return visit to cut back, and basic patching.

Where jobs get more expensive: if the wall is rendered, tiled or lined and has to be stripped and reinstated; if the crack turns out to be a construction joint running the full length of the wall rather than a discrete crack, which is priced per linear metre at roughly $200 to $500; if there is a fit-out, shelving or a car to protect and work around; and if the garage is a long way from base.

Where they get cheaper: several cracks on one visit share the same set-up cost, so the per-metre rate drops. A single short crack is priced as a minimum job, not as a rate, because no contractor can travel, set up a pump, inject, and return to make good for less than the attendance minimum of roughly $450 to $900.

In Queensland, trade work valued over $3,300 including labour, materials and GST must be done by an appropriately licensed QBCC contractor. Most garage wall repairs sit either side of that line, so it is worth asking, and worth checking the licence number against the QBCC register rather than taking a logo on a ute at face value.

Three questions that separate a real quote from a cheap one

You do not need to understand resin chemistry to tell a proper quote from a bad one. Ask these three, and compare the answers rather than the prices.

• Are you drilling and using mechanical packers, or gluing ports to the surface? Surface ports rely on a bead of filler sticking to the face of the wall. On a wall that is actively leaking, it will not adhere and it blows off. Ports are legitimate for some dry structural work; on a wet garage wall they are a warning sign.
• Which resin are you using, and why that one for this wall? Hydrophilic and hydrophobic polyurethane behave differently in a wall that dries out between wet seasons, and a contractor who cannot tell you which one is going into the crack, or why, is working from a single product rather than from a diagnosis.
• Is making good included, and is the price per crack or per linear metre? Cutting the packers back, filling the holes and grinding flush is often quoted as included when it is not. If the wall needs re-rendering and painting, get that in writing as its own number.

How you know it worked

During injection, the proof is resin appearing at the next packer along. That is direct evidence it has travelled through the crack rather than sitting in the hole.

Afterwards, the area should be watched for at least 24 to 48 hours and, wherever the weather allows, through an actual rain event. In South East Queensland the honest test window is the wet season, roughly November to March, when the ground stays saturated for days rather than hours. Moisture meter readings at marked points before and after give a number to compare rather than an opinion.

The record matters as much: photographs before and after, taken from the same positions, and a written description of what was found and what was done. That is worth more than it sounds. If water reappears in two years, the record establishes whether the original repair has failed or a new path has opened somewhere else — and those two things have very different answers.

What it costs

Indicative market bands only, excluding GST, and not an offer from anybody. The working behind the rates — what each line covers, which loadings apply and where published Australian figures disagree — is set out in the 2026 cost guide.

Common questions

There is no crack I can find, but the wall is wet along the very bottom. What is that?

Almost certainly the kicker joint — the horizontal line where the wall was poured onto the floor slab. Two separate pours never fully bond, so that joint runs continuously along the base of every wall and it is the most common water path in an under-house garage. It is injectable, with fittings at roughly 200 to 400 mm centres along the joint, and a crew typically covers 8 to 15 linear metres of it a day depending on how hard the water is running.

It only comes in during the wet season and the wall is bone dry by August. Does that change the repair?

It changes the resin. There are two families of polyurethane. Hydrophilic resin loves water — it chases the leak into fine cracks and grips damp concrete beautifully, but it holds water inside itself, so a wall that dries out completely for months can cause it to shrink and lose its grip in the crack. Hydrophobic resin uses water to set but does not absorb it, so it stays the same size through wet and dry cycles. For a wall that dries out every winter, hydrophobic is usually the safer choice, and that is a judgement about your specific wall rather than a rule.

Can I just paint the inside with a waterproofing paint from the hardware shop?

It will hide the stain for a while and it will not stop the water. Coatings applied to the inside face are being pushed off the wall by the water pressure behind them rather than held on, so they blister, flake and lift. Worse, a coating that partly works spreads the damp sideways to the next weak point rather than removing it. Where a coating does belong is over the top of a completed injection, as a second line of defence on a wall that has already had its water path sealed.

How much of the garage do I need to empty out?

Enough clear space along the affected wall to stand, drill at an angle and run a hose — usually about a metre and a half. Everything within a couple of metres should be covered or moved, because cured polyurethane is very difficult to remove from anything it drips onto, and prevention is far quicker than removal. Cars should not be in the garage during injection for the same reason. Drilling is dusty and noisy for the first part of the day, and there is a chemical smell during injection that clears with ventilation, usually the same day.

Is the resin dangerous with kids and pets in the house?

The uncured resin contains isocyanates, which are a genuine respiratory hazard for the people handling them. That is why technicians wear proper fitted respirators and gloves, and why an enclosed garage has to be ventilated. The Australian workplace exposure standard is 0.02 mg per cubic metre averaged over eight hours, and sensitisation is permanent, so it is taken seriously by anyone competent. Once the resin has reacted, which happens within minutes, it is an inert plastic. In practice: keep people, pets and food out of the work area during injection and until the space is ventilated, which is the same day. Ask for the safety data sheet for every product used - that is an entitlement, from any contractor.

The ground on my neighbour's side is higher than my garage. Does that make it their problem?

Water arriving from higher ground next door is common on the hillside blocks around Brisbane and the Gold Coast, and it is a legal question about the wall, the boundary and any drainage easement rather than a technical one. What can be done first is to document it properly: where the water is coming from, what the levels are, whether a subsoil drain exists and whether it discharges. A photographed, measured record of that is what any conversation with a neighbour, a body corporate or a solicitor is going to need, and it is worth having before the repair rather than after.

My builder says it is just shrinkage cracking and nothing to worry about. Is that right?

Often it is. Concrete shrinks as it cures and fine cracking is normal — the Australian concrete design standard AS 3600 allows for cracks of roughly 0.1 to 0.4 mm depending on the type of element and how exposed it is. The question is not whether the crack exists but whether water is coming through it and whether it is getting wider. A dormant hairline crack in a dry wall genuinely needs nothing. The same crack passing water needs sealing, because water sitting against the reinforcing steel inside the concrete eventually corrodes it, and that is a far more expensive problem than the one you have now.