Injection is the method of closing a water path by forcing resin under pressure into a crack in the concrete or into the void behind a retaining wall. It was developed for situations where the outer face cannot be excavated and water is actively flowing.
When it is used
Where the outer face of the wall cannot be reached because of a neighbouring plot, a road or an existing structure. In basements built with bored piles or diaphragm walls. In lift pits, water tanks and plant rooms entirely surrounded by fill. Where work is needed while the building is in use and vacating it is not possible.
By contrast, in a basement sweating across the whole wall face the problem is usually concrete permeability or condensation. That calls for surface waterproofing and ventilation, not injection.
Resin types
Polyurethane foam
Expands into a foam on contact with water. Used to cut off active, pressurised flow. Its job is to stop water, not to repair structure.
Flexible polyurethane
Does not foam and stays elastic after curing. Used in moving cracks and joints, where it can follow structural movement.
Acrylic gel
Its viscosity is close to that of water, so it penetrates fine hairline cracks and the ground behind the wall. Used to form a sealing barrier between wall and soil.
Epoxy
Gives high bond and compressive strength and is rigid. It structurally reunites the two faces of a crack. Not preferred in moving cracks or wet conditions.
Application steps
Investigation. A crack map is produced and moisture readings taken. The point where water enters is often not the point where it appears.
Drilling. Angled holes are drilled alternately either side of the crack line, driven so as to intersect the crack at mid depth.
Packer installation. Mechanical or drive in packers are fitted into the holes and tightened.
Injection. Resin is pumped starting from the lowest packer and working upwards in sequence. Resin appearing at the neighbouring packer shows that section is full.
Completion. After curing, packers are removed and hole mouths made good with repair mortar. Where required, a crystalline or cementitious system is applied to the surface.
What makes the result last
Injection cuts off the water but does not change why the water is there. Managing surface water around the building, adding internal drainage where possible and completing the wall face with a system that works on the negative side determine durability. The area should be observed through the first wet season.
Frequently asked
Can it be done while the building is occupied
Yes. The work is carried out from inside, requires no excavation and is confined to a limited area. Adequate ventilation is enough.
Is the concrete damaged
The holes are small relative to the concrete section and are positioned after scanning for reinforcement. Correctly executed, there is no structural loss.
How long does it take
A limited crack line is usually completed within a day. Work with many injection points spreads over several days.
If water is actively entering your basement, seeing the crack line and the flow rate on site is necessary to choose the right resin.