If water is running into a basement through the retaining wall and excavating the outer face is not possible, the solution is injection. The method works by forcing resin under pressure into the crack or into the void behind the wall to close the water path. This article covers when injection is the right answer, which resin does what, and how the work proceeds.
When injection is the right solution
Injection was developed for situations where the outer face is unreachable and water is actively flowing. Where a foundation can be excavated, conventional waterproofing applied from outside is always more durable. The typical cases for injection are as follows.
Where a neighbouring plot, a road or an existing structure prevents excavation at the outer face of the wall. In basements built with bored piles or diaphragm walls, where the outer face is inaccessible by design. In lift pits, water tanks and plant rooms that are entirely surrounded by fill. Where work is required while the building is in use and vacating it is not possible.
By contrast, injection is not the answer to widespread, diffuse damp. In a basement sweating across the whole wall face the problem is usually the permeability of the concrete or condensation, and that calls for surface waterproofing and ventilation.
Resin types and what each does
Polyurethane foam resins
React rapidly on contact with water and expand into a foam. Used to cut off active, pressurised flow. Their primary job is to stop water, not to repair structure.
In a high flow leak this is usually the first step. Once the water is cut off, a durable resin can be used in a second stage where required.
Flexible polyurethane resins
Non foaming types that remain elastic after curing. Used in moving cracks and joints. Because the resin can follow structural movement, the crack does not reopen.
Acrylic gels
Their viscosity is very close to that of water, so they can penetrate fine hairline cracks and reach the ground behind the wall. Used to create a sealing barrier between the wall and the soil. The gel time can be adjusted, which gives the applicator control.
Epoxy resins
Provide high bond and compressive strength and are rigid after curing. Used to structurally reunite the two faces of a crack. Not preferred in moving cracks or wet conditions, because a rigid material cannot accommodate further movement and adhesion weakens in the presence of water.
How the work proceeds
Investigation
The point where water enters and the point where it appears may not be the same. Water travels horizontally within the concrete and behind finishes. A crack map is therefore produced first, moisture readings are taken and finishes are opened to a limited extent where necessary.
Drilling packer holes
Angled holes are drilled alternately either side of the crack line. The holes are driven at an angle so as to intersect the crack at mid depth, allowing the resin to reach the body of the crack. Hole spacing is set according to wall thickness.
Installing packers
Mechanical or drive in packers are fitted into the holes and tightened. The packer is the fitting that the injection pump connects to and that delivers resin without losing pressure.
Injection
Resin is pumped starting from the lowest packer and working upwards in sequence. Starting from the bottom fills the void from below and avoids trapping air. Resin appearing at the neighbouring packer shows that section is full and the pump moves on.
Completion
Once the resin has cured the packers are removed and the hole mouths made good with repair mortar. Where required, a cementitious or crystalline system is applied to the surface to complete the seal.
What makes injection last
Injection cuts off the water but does not change why the water is there. If the water load around the building continues, it may in time emerge at another weak point. The following should be considered for a durable result.
Removing surface water. The falls around the building, the discharge points of rainwater downpipes and the pavement detail should all be checked. Most of the water can often be taken away from the building by simple surface work.
Internal drainage option. Where external drainage is impossible, a collection channel and pumping chamber can be built at the foot of the wall inside the basement. This lowers the pressure on the wall.
Completing the surface waterproofing. Injection is a local solution. Applying a system that works on the negative side across the whole wall face reduces the risk of water emerging at new points.
Monitoring. The treated area should be observed through the first wet season, with early intervention if a new damp mark appears.
Frequently asked
Can it be done while the building is in use? Yes. Injection is carried out from inside, requires no excavation and is generally confined to a limited area. Adequate ventilation is enough.
How long does it take? It depends on the length of the crack and the rate of flow. A limited crack line is often completed within a day. Extensive work with many injection points spreads over several days.
Is the concrete damaged? The holes drilled are small relative to the concrete section and are positioned after scanning for reinforcement. Correctly executed, there is no structural loss.
Can it be done in winter? The cure time of the resins varies with temperature. At low temperatures curing takes longer but application is possible. The minimum temperature in the manufacturer data sheet must be observed.
Summary
Injection is an effective method for basements where the outer face cannot be reached and water is actively flowing. Choosing the right resin, drilling the holes at an angle that intersects the crack and injecting in sequence from the bottom upwards are the three fundamentals of the technique. Durability depends on treating injection not on its own but together with surface water management and surface waterproofing.
If water is actively entering your basement, seeing the crack line and the rate of flow on site is necessary to decide on the right resin and the right method.