Injection waterproofing: resins, gels, curtain injection

When injection is needed

Injection waterproofing is the pumping of liquid materials into cracks, construction joints, honeycombing and voids in concrete and masonry and, in curtain injection, into the ground behind the structure. It is used when water is already coming in: in basements, car parks, tunnels, manholes, lift pits and tanks in service, as well as in construction joints where injection hoses were cast in during concreting. The main advantage is that the work is done from the inside, without excavation and without dismantling the structure.

Waterproofing injection addresses watertightness. If a crack has weakened the structure and its monolithic integrity and load-bearing capacity need to be restored, force-transmitting filling with epoxy resins is used — this is covered in the “Crack injection” section under concrete repair. Both tasks are often tackled in sequence: first the water is stopped, and then, once the crack has dried out, monolithic integrity is restored.

Materials

Rapid-setting hydraulic mortars — for point leaks, holes and leaking joints, including under pressure. The mortar is pressed into the cut-out area and held until it sets: for Mapei Lamposilex this takes about 1.5 minutes, while for Xypex Patch’n Plug the initial set occurs after 1.5–4 minutes. This is the first step before cementitious or penetrating waterproofing.
Foaming polyurethane resins — react with water and within seconds turn into a foam that shuts off a heavy inflow. Sika Injection-101 RC foam expands up to 40 times in volume, and Mapei Resfoam 1K-M up to 44 times; Fosroc Nitofill WS60 is designed for cracks from 0.2 to 5 mm wide. This is a temporary measure: the foam stops the water, but permanent watertightness is provided by the next stage.
Elastic polyurethane resins — for permanent sealing of dry, damp and wet cracks and construction joints. They remain elastic and accommodate small crack movements. In the catalogue: Sika Injection-201 CE with a viscosity of about 100 mPa·s, marked to EN 1504-5 as a product for ductile filling.
Acrylate gels — a viscosity close to that of water and an adjustable reaction time. They are used to seal fine cracks and joints, to restore damaged waterstops and to carry out curtain injection. An example is SikaInject-304 DE, with a mixed viscosity of about 4 mPa·s; the cured gel is elastic and swells on contact with water.
Microfine cement suspensions — for filling large voids and for injection hoses where mineral compatibility and the possibility of re-injection are important; they are selected within the same manufacturer’s system.

What EN 1504-5 says

The European standard EN 1504-5 describes concrete injection products in three categories: force-transmitting filling (F), ductile filling (D) and swelling filling (S) of cracks, voids and interstices. Resins and gels for permanent sealing are marked to this standard. But the standard explicitly does not cover preliminary injection to stop water temporarily, or the filling of voids outside the structure — in the ground or at the structure–ground interface. That is why foams for stopping leaks may have no EN 1504-5 marking, and for curtain injection other documents are checked: for SikaInject-304 DE, for example, it is a German general building approval for curtain injection.

How injection is carried out

Survey. Where the water is coming from, whether it is under pressure, the width and movement of the cracks, the moisture, the location of reinforcement and services. At this stage, it is decided whether the water needs to be stopped temporarily first or whether permanent sealing can be carried out straight away.
Pressure relief and stopping a heavy inflow. Under a high head, the pressure is first relieved through a drain tube, then the water is stopped with foam or a hydraulic mortar. At high pressure and with wide cracks, the resin may not be able to cope with the flow — this is noted, for example, in the Fosroc Nitofill WS60 data sheet.
Installing packers. Holes are drilled in a staggered pattern on both sides of the crack, at an angle, so that they intersect the crack within the thickness of the structure. The spacing is set by the material’s data sheet and the thickness of the structure: for Fosroc, it is usually 200–500 mm. The exposed crack between the packers is usually sealed with a compound specified by the manufacturer so that the resin does not run out; with a heavy flow, this surface sealing is sometimes omitted.
Injection. On vertical cracks — from the bottom upwards, starting with the lowest packer; on horizontal cracks — from one end. Wherever possible, each crack is treated in one continuous cycle. Single-component pumps are used for one-component polyurethanes, and two-component pumps for acrylate gels and products with an accelerator.
Permanent sealing. After the temporary foam, the crack is re-injected with an elastic resin or gel — according to the Sika Injection-201 CE data sheet, for example, where there is a heavy inflow under pressure, a foaming resin must be injected first.
Completion. The packers are removed, the holes are filled with repair mortar and, where necessary, the surface is covered with a penetrating or cementitious compound.

Curtain injection

If water comes through a large area rather than through individual cracks — old masonry, concrete with many defects, walls without external waterproofing — curtain injection is carried out. Holes are drilled through the wall on a grid, and acrylate gel is pumped into the ground behind the structure. The gel permeates the soil and, once cured, forms a watertight screen on the outer face of the wall, even though the work is carried out from the inside. The reaction time of the gel is set to suit the soil and the temperature: for curtain injection, the SikaInject-304 DE data sheet recommends more than 2 minutes so that the gel has time to spread. The hole spacing, injection volume and sequence of work are determined from the results of the survey, taking the soil into account.

Safety

Polyurethane resins contain isocyanates, and acrylate gels contain reactive components. The work is carried out wearing skin, eye and respiratory protection, with ventilation and, in confined spaces, with forced air exchange. Material residues and flushing liquids are disposed of as instructed in the safety data sheet.

Common mistakes

Foam taken for a permanent repair — the leak returns within a few months.
A rigid epoxy resin in a moving crack or joint — the crack opens alongside.
The packers do not intersect the crack or are spaced too far apart — the material does not reach the water.
Excessive injection pressure — spalling of the concrete and new cracks.
Injection without pressure relief under a high head — the resin is washed out before it reacts.
The cause has not been eliminated: water keeps coming in through unsealed joints and pipe penetrations or because there is no drainage, and the leak “moves” to the adjacent area.
The reaction time of the gel has not been checked with a trial mix at the actual temperature.

Materials in the catalogue

Sika Injection-101 RC — Sika — fast-foaming PU injection resin for temporary stopping of heavy water ingress.
Sika Injection-201 CE — Sika — elastic PU injection resin for permanent sealing of cracks and construction joints.
SikaInject-304 DE — Sika — polyacrylate gel for curtain injection and permanent sealing of cracks and joints.
Resfoam 1K-M — Mapei — one-component PU injection resin for stopping water seepage in concrete and ground.
Fosroc Nitofill WS60 — Fosroc — PU injection resin for temporary stopping of water flow in concrete cracks.
Lamposilex — Mapei — ultra-rapid hydraulic binder for instant stopping of leaks, including water under pressure.
PeneSplitSeal — Penetron — two-component polyurethane injection resin for cracks, joints and damp-proof barriers.
PenePurFoam — Penetron — water-reactive polyurethane foam resin (N, NR, R) for leaks and damp-proofing.
PenePurFoam 1K — Penetron — one-component water-reactive resin with catalyst forming flexible foam.
PenePurFoam 65 — Penetron — water-reactive resin with catalyst forming rigid foam to stop pressurised leaks.

Frequently asked questions

Can a basement leak be stopped without excavation?

In most cases, yes: point leaks are stopped with hydraulic mortars, cracks and joints by injection, and leaks over a large area by curtain injection from the inside. After that, the surface is usually protected with a penetrating or cementitious compound.

How does polyurethane differ from acrylate gel?

Polyurethanes come in foaming grades, for stopping water quickly, and elastic grades, for permanent sealing of cracks and joints. Acrylate gels are more fluid, penetrate the finest cracks and the soil, and their reaction time can be adjusted; they are used for curtain injection and for repairing damaged waterstops.

How long does injection waterproofing last?

Permanent sealing with elastic resins and gels is designed for long-term performance, provided the right material has been chosen and the causes of the leak have been eliminated. Temporary foam offers no such durability — it is the first stage.

Can a crack be injected while water is coming through it under pressure?

Yes, but first the pressure is relieved and the flow is stopped with a foaming resin or a hydraulic mortar, and then permanent sealing is carried out.

Rapid-setting compounds for stopping running water before the main waterproofing are in the section Hydraulic plugs.

We will stop the leak and select materials for permanent sealing — call us or message us on WhatsApp/Telegram: +998 94 094 52 27.