The crack you can see is very often not where the water gets in. Water enters at one point, travels laterally between layers, and exits at the weakest one — sometimes metres away. These two cross-sections mark every genuine entry point in the two building types we are called to most, and say plainly which ones injection can fix.
The most common residential arrangement in South East Queensland: a cut into the slope, a retaining wall holding the ground back, and a garage or rumpus room built against it.
Pick a point
Every marked point is somewhere water genuinely gets into a building like this one. Choose one and you get what fails there, whether injection is the right answer at that specific point, and what to do instead when it is not.
Injection is the right fix here
Sometimes — depends what is behind it
Injection will not fix this
Every entry point, written out
KICKER JOINT
The joint where the wall meets the floor
The construction joint at the base of a poured wall — the wall goes in after the slab, and the two never truly bond. It is a dead straight, level line, and it is the single most common entry point in this kind of build. People almost always blame a crack they can see higher up instead.
Injection is the right fix here.Injection through mechanical packers at 200–400 mm centres. Joints take more resin and closer packers than a crack of the same length.
Shrinkage, settlement or thermal movement opens a path straight through the element. Under a head of water it will weep or run. Width matters: roughly 0.1–0.4 mm sits within normal serviceability limits for reinforced concrete, so the question is whether it leaks, not whether it exists.
Injection is the right fix here.Polyurethane injection from the dry side. The resin choice depends on whether the crack ever dries out permanently — that is the whole decision.
Water travels through the mortar joints and any unfilled cores rather than through the blocks themselves. If the cores were never filled they will swallow resin indefinitely without ever sealing the wall.
Sometimes — depends what is behind it.Check the drainage first — clearing a blocked ag line and the weep holes is sometimes the entire fix. If the wall leans, bulges or shows stepped cracking through the mortar joints, stop and get an engineer.
A slotted pipe in gravel, meant to collect groundwater and take it away before it ever loads the wall. They silt up, get crushed, get built over, or were never connected to anything in the first place. A blocked ag line turns a drained wall into a dam.
Injection will not fix this.Find the outlet and confirm water actually runs out of it during rain. It is the first thing to check and the last thing anyone checks.
Deliberate openings that let water out at the bottom of the wall. On a rendered or painted wall they are frequently sealed over by a later trade who did not know what they were for.
Injection will not fix this.Clear them. Sealing the face of a wall whose weep holes are blocked raises the retained water head on a structure that may never have been designed for saturated backfill.
Surface water running toward the building instead of away from it, or a downpipe discharging straight into the fill behind the wall. No waterproofing system will beat a few thousand litres delivered directly to the back of the wall during a storm.
Injection will not fix this.Regrade, or redirect the downpipe. Cheap, unglamorous, and frequently the whole answer.
Under hydrostatic pressure water comes up through a slab crack as readily as it comes through a wall. In a garage it usually shows as a damp patch that never quite dries, often with a white bloom around the edge of it.
Injection is the right fix here.Injection works, but watch the resin budget: a void or drainage layer under a slab will take resin indefinitely. Hard stop at 1–2 litres per packer.
In South East Queensland humidity, a closed garage against cool below-ground concrete produces condensation that looks exactly like water coming through the wall. It is constant, it does not track rainfall, and it is the most common misdiagnosis in this trade.
Injection will not fix this.The 48-hour plastic sheet test settles it. Moisture on the room side means condensation; moisture behind the plastic means water is moving through the wall.
Water gets through the deck above, travels laterally between the topping and the structural slab, and exits at the weakest point — often metres from where it entered. Calcite stalactites hanging from the soffit mean the flow has been chronic rather than recent.
Injection is the right fix here.Map the structural slab against the topping before injecting anything. If the slab is post-tensioned it must be GPR scanned and the drilling approved in writing by an engineer first.
A planter is a permanently wet box sitting on a structural slab. Membranes fail, outlets block, roots find every defect, and fertiliser salts attack the concrete. It stays wet year round, which changes the resin choice.
Sometimes — depends what is behind it.Injection is usually an interim measure here — the honest answer is often that the membrane needs replacing. Sealing without restoring the outlet turns the planter into a bathtub and loads the structure.
The pit is the lowest point in the building, so it collects everyone else's water as well as groundwater. Buffer and hydraulic oil contamination is the most common reason a pit repair fails — resin will not bond through oil.
Injection is the right fix here.Degrease first, then inject. A confined space under AS 2865: permit, atmospheric testing, standby person and rescue plan, and the lift contractor does the isolation and lock-out.
A tie hole is a straight pipe through the wall — the most direct water path in the entire building. Mortar-only plugs shrink as they cure, the annulus reopens, and it weeps again. A basement wall can have hundreds of them.
Injection is the right fix here.Cut any remaining steel tie back 25–40 mm, then inject. Count them at quoting stage: a crew does 20–50 a day.
Where one pour met the next. If the waterstop was displaced during the pour, or there was never one, the joint is a continuous path across the full width of the wall.
Injection is the right fix here.Injection at 200–400 mm centres, or an injection hose retrofit. Never inject a designed movement joint — that is a backing rod and movement-capable sealant scope.
Water moving through the body of the concrete rather than along one path. There is no crack to seal, so crack injection has nothing to work on.
Injection will not fix this.A drained cavity system, crystalline tanking, curtain injection or excavation — all different trades to ours. We will tell you which one you are looking at rather than injecting a crack that is not there.
Run the leak diagnostic, or send three photos. Between the two, most leaks can be identified without anyone attending — and we will tell you if it turns out to be somebody else's trade.