Stopping Water Leaks with Injection: How Does It Work?

• Ahmet Toka
• 7 August 2026
• Waterproofing
• 4 min read

Most waterproofing methods share one condition: the surface must be dry. Injection is the exception to that rule. It can be applied while water is flowing; indeed, some resins work precisely because they come into contact with water. This property makes injection indispensable in occupied buildings, car parks, lift pits and tunnels.

In this article we explain what injection is, which resin is used in which situation, how the application proceeds step by step on site, and what the limits of the method are. At the end you will also find a realistic answer to the question "is injection permanent?".

Injection stops the water but does not change the reason it is coming. If structural movement continues, the crack reopens; this is why the cause is identified first.

Ahmet Toka, General Manager

What Is Injection?

Injection is the process of pumping liquid resin under controlled pressure into a crack, cold joint or void in a reinforced concrete element. The resin fills the void and, once cured, physically closes the path the water travels.

The method's greatest practical advantage is its low level of intervention. No excavation, removal of finishes or extensive breaking out is required; only small-diameter packer holes are drilled along the line of the crack. For this reason it can be applied in occupied buildings without stopping activity.

Its second advantage is access. Wherever the external face the water comes from cannot be reached (basement retaining walls, lift pits, tunnel linings, retaining walls), injection is one of the few methods that can work from inside.

Resin Types and the Logic of Selection

Resin selection determines everything about the injection. An application made with the wrong resin fails even if it is carried out correctly.

Polyurethane Foam Resins

On contact with water it reacts, foams rapidly, expands and fills the void, stopping the water. Actively leaking cracks are its main application. Because its expansion ratio is high it can also fill irregular voids. Its purpose is to cut off water; it does not provide structural bonding.

Elastic Polyurethane Resins

These types remain flexible once cured. They are used in cracks that open and close because of temperature differences or small structural movements. Where a rigid filler would break, an elastic resin follows the movement and maintains the seal.

Epoxy Resins

Low-viscosity epoxy is injected into dry and non-moving cracks to restore the integrity of the section. Because it reaches a higher strength than concrete once cured, it is used in structural repair. It is not used in a crack where water is present; water prevents the resin from bonding to the concrete. For details on this see our crack repair page.

Acrylic Gels

Thanks to their near-water viscosity they penetrate very fine hairline cracks and voids in the ground. They are also used to form an impermeable curtain between the structure and the soil by injecting behind a retaining wall. This application is called curtain injection and is an important option in structures that cannot be reached from outside.

Application Steps

1. Assessment and analysis. The width and depth of the crack, whether it is moving, and whether water is entering are all determined. The choice of resin rests entirely on this assessment.
2. Packer plan. Holes are drilled along the crack line at an angle that intersects the crack. The spacing is determined by the element thickness; the general approach is for the hole depth to be around half the element thickness and for the holes to intersect the crack at mid-depth.
3. Packer installation. Mechanical packers are inserted into the holes and tightened; they are fixed so that they cannot be dislodged under pressure.
4. Surface sealing. The visible face of the crack is sealed with rapid-setting mortar so that the resin does not escape.
5. Injection. Pumping starts at the lowest packer and works upwards. Product emerging from the packer above indicates that section is full. Pressure is increased gradually; a sudden high pressure can crack the concrete.
6. Cleaning and checking. After curing the packers are removed, the holes are made good with repair mortar and the surface is levelled. The cessation of leakage is confirmed by observation; a second pass is carried out if necessary.

For application details see our injection applications page.

Where Is It Used?

• Basement retaining walls: Stopping active leaks on surfaces that cannot be reached from outside.
• Lift pits: Narrow, hard-to-reach spaces where water collects.
• Car park decks: Leaks dripping from the floor above to the one below.
• Tunnels and underpasses: Water coming through segment joints and cold joints.
• Water tanks and treatment structures: Emergency intervention in spaces that cannot be emptied.
• Retaining walls: Situations where the soil side cannot be accessed.
• Cold joints: The junction lines between concrete poured at two different times.

Is Injection a Permanent Solution?

The direct answer: if the crack is not moving and the reason the water is coming has not changed, yes, it is permanent. The resin has filled the void and stays there.

The cases where it is not permanent are equally clear. If there is settlement, post-earthquake movement, heavy vibration or continuous thermal expansion and contraction, the crack can reopen. Two things are then done: an elastic resin is selected to give a degree of movement tolerance and, more importantly, the cause of the movement is addressed structurally. If necessary, intervention in the load-bearing system is planned with reinforced concrete strengthening .

Another limit is wide voids. In very wide voids the volume is first reduced with a filling mortar and injection is then carried out. Injection is also a localised solution; if there is widespread permeability across the whole surface, then instead of a point intervention crystalline or cementitious surface systems are more appropriate.