What a correct injection repair involves

11 steps, in the order they happen on site

The ordering matters as much as the content. Diagnosis is the highest-value step in the whole job and the one most often skipped, which is why it occupies the first two positions and why neither of them involves any equipment.

1. Establish where the water is actually getting inBefore anything is drilled, the path has to be established. The crack that is visible is often not the entry point — water tracks laterally between a membrane and the concrete and exits at the weakest point, which can be metres from where it started.
2. Rule out the things injection cannot fixBlocked ag lines, failed membranes, condensation, rising damp, leaking services, structural movement. If it is one of those, the correct outcome is to stop. This is the step most quotes skip, and it is the one that decides whether the money is well spent.
3. Scan before drilling where the slab may be post-tensionedGround-penetrating radar and written engineer approval on any suspended or post-tensioned slab. A cut tendon is not a repairable mistake, and no schedule pressure justifies skipping it.
4. Set out the packer positionsHoles at 150–400 mm centres, closer where the path is diffuse, and never spaced further apart than the element is thick.
5. Drill at 45 degrees, offset from the crack13 mm holes, offset from the crack line by roughly half the element thickness so the hole intersects the crack at depth, drilled to two-thirds or three-quarters of the thickness. Never straight through — a hole that exits the far face gives the resin somewhere to escape and gives the water a new path.
6. Flush the holes with waterThis does two jobs: it proves the packers are connected to each other through the crack, and it pre-wets the crack, which a water-reactive polyurethane needs in order to cure properly.
7. Fit mechanical packersSteel or alloy packers set into the drilled holes, which take injection pressure. Surface ports glued to the face will not adhere to a wet wall, which is why cheap wet-wall repairs fail.
8. Kill heavy flow firstWhere water is running rather than weeping, a hydraulic plug or oakum goes in first so the resin is not simply washed out before it can react.
9. Inject bottom to topStarting at the lowest packer and moving up only when resin shows at the packer above. That confirms the crack is filling continuously rather than the resin finding one easy path.
10. Leave the packers in for 24 hoursThen cut back, remove them, and make good. Cutting the packers off the same day is how it emerges later that the resin had not finished doing its job.
11. Re-inspect after rainRe-inspection after 24–48 hours and after the next real rain event, photographed from the same positions as the before shots so the change is measurable rather than remembered.

Pressure bands

Pressure is chosen for the element, not for the machine. Too little and the resin never reaches the far side of the crack; too much and the crack widens, mortar beds blow out, or a thin slab lifts.

What the record should look like afterwards

At minimum: photographs, and a written description of what was found and what was done about it. Before and after shots taken from the same positions are genuinely comparable; two pictures of roughly the same wall are not, and the difference only becomes apparent when there is an argument about whether anything changed.

On larger commercial work the standard goes further — a numbered packer map, resin batch numbers, and the volume injected at each point. That is real work to produce and it is not standard on domestic jobs, so where an engineer or a body corporate requires it, it belongs in the scope at tender stage rather than being assumed and argued about later.

The one item worth insisting on regardless of job size is a re-inspection after rain, agreed in writing before the work starts. A repair that has not seen water has not been tested.

Safety, stated plainly

• Confined spaces. Lift pits, tanks and some plant rooms are confined spaces under AS 2865. That means a permit, atmospheric testing, a standby person and a rescue plan — typically $800–$2,000 a day, which should be itemised on a quote rather than hidden in a rate.
• Silica dust. Drilling concrete generates respirable crystalline silica, with a workplace exposure standard of 0.05 mg/m³. On-tool extraction or wet drilling, every time, and worse in an enclosed basement where the dust has nowhere to go.
• Isocyanates. Uncured polyurethane resins contain them and sensitisation is permanent. People should be kept out of the immediate work area during injection, and the safety data sheet for every product used is something a property owner is entitled to ask for.

When a competent contractor should refuse

There are situations where the correct professional answer is to decline the work: a designed movement joint, a wall that is still moving, a slab that has not been scanned, or a crack where the real problem is drainage. None of those are fixed by resin, and injecting them makes the eventual repair harder.

A negative-side seal also should not be described as making a basement permanently dry, because sealing redirects water rather than removing it. That distinction is the single most common source of dispute after an otherwise competent repair, and it is why the redirection risk belongs in writing before the work, not in a warranty argument afterwards.