Leaks Back After Injection? Repairing a Failed Basement Injection Job

The basement was injected, the walls dried out, and a few months later the stains are back. Re-injecting the same cracks the same way usually gives the same result. A failed injection job has to be diagnosed before it is repaired. This is how we approach one.

Why injection repairs fail

Injection is a reliable method, but it fails for a small number of reasons, and most of them can be read from the wall:

• Foam only, no permanent seal. Water-reactive polyurethane foam stops flowing water, but it is a temporary stage. Without a flexible second resin injected after it, the foam shrinks and the crack opens again with the next wet season.
• The wrong resin for the crack. A rigid epoxy in a joint that still moves cracks beside itself. Construction joints and shrinkage cracks in retaining walls need a flexible resin.
• Ports that never reached the crack. Holes drilled straight into the crack face, or too shallow, fill the surface and leave the crack inside the wall dry of resin. The ports should be drilled at an angle to cross the crack at about mid-depth.
• Packers too far apart, or pressure too low. The resin never travels from one packer to the next, so lengths of crack between them stay open.
• No surface seal. Resin escapes from the face of the crack instead of filling it.
• The water source was never stopped. If the water comes from a leaking pipe, a fire main or a tank rather than groundwater, injection only moves it to the next weak point.
• New cracks, not old ones. Sometimes the injected cracks are holding and the seepage is at new locations nobody mapped.

Diagnose before re-injecting

Before pricing a re-injection we survey the basement against whatever record the first job left, and answer three questions for every wet location:

1. Where exactly is the water? Through the old packer holes, along the crack between them, beside the injected line, or at a location that was never treated.
2. What is the water? Groundwater, rainwater or mains water. Mains water is often chlorinated and appears all year, while groundwater seepage follows the season. If the water is not groundwater, the source is found and stopped first.
3. What was used? The data sheets from the first job, if the owner has them, show whether a flexible permanent resin was used at all.

The result is a numbered leak schedule, level by level, that separates failed locations from new ones. It is also the document an owner needs to raise the matter with the first contractor while the defects period is still running.

How a failed location is re-injected

1. Old surface packers and loose repair material are removed, and the crack line is cleaned and sealed again.
2. New ports are drilled offset from the old ones, at an angle that crosses the crack inside the wall, at a closer spacing. Cured foam left in the crack blocks resin, so the new holes go where the crack is still open.
3. Where water is flowing, a water-reactive foam stops it first.
4. The permanent seal follows: a flexible polyurethane resin whose data sheet states its EN 1504-5 class, injected from the lowest packer upward until resin appears at the next one.
5. After cure, every location is re-inspected against the schedule, any point still showing water is re-injected, and the holes are reinstated with non-shrink repair mortar.

The method in detail, including the inspection hold points, is in what consultants check in an injection method statement.

What to ask for the second time

A building that has already paid for one injection job should not accept a vague scope for the second:

• A cause for each failed location, written in the survey, not just a new price.
• A two-stage method with the permanent resin named and its EN 1504-5 class stated.
• A completion criterion: verified dry at each location after cure, with re-injection included until it passes.
• A before-and-after photo record and a marked-up layout of every treated location, so the next defects period starts from a clear record.

Re-injection locations often cost more than first-time ones, because old packers and repairs have to be removed and the new ports placed around cured resin. Pricing per location against the schedule keeps that visible. How to set the schedule, the method and the commercial terms is covered in what to put in a basement chemical injection RFQ.

A typical case

We were recently asked to price the repair of a multi-level basement in Abu Dhabi where injection by another contractor had failed within a few months. Seepage was back at construction joints on several levels. The scope we offered was injection only: a survey and numbered schedule first, then two-stage injection per location, with walls and floor slabs measured separately and the quantities split by level so the owner could release the work one level at a time.

If leaks have come back in a building you manage, see chemical injection waterproofing or leak repair for managed buildings.