What is injection?
Injection is the filling of cracks and voids in concrete with a liquid material, under pressure or by gravity, through packers. The aims vary: to restore monolithic integrity and load-bearing capacity, to cut off the path of water and aggressive substances to the reinforcement, to stop a leak, or to fill voids behind cladding or under a slab. The material depends on the aim.
EN 1504-5 divides injection products into three groups according to their purpose: for force-transmitting filling of cracks and voids (F), which transmits forces; for ductile filling (D), which remains flexible; and for swelling filling (S). Epoxy resins belong to the first group, polyurethane and acrylate compounds to the second and third. Preliminary waterproofing injection to stop water is not covered by the standard; such products are described in the “Waterproofing” section.
Where the choice begins
Before choosing a resin, several questions have to be answered.
- Why the crack appeared. Shrinkage, overloading, settlement, thermal movement, reinforcement corrosion. If the cause is still active, filling the crack without eliminating it will produce a new crack alongside.
- Whether the crack is moving. A dormant crack can be rigidly bonded with epoxy resin. A crack whose width changes with temperature or load cannot be held by a rigid resin — an elastic material or a movement joint is needed.
- How wide and deep the crack is, and whether it passes right through. The viscosity of the resin and the packer spacing depend on the width; manufacturers state a maximum width — for Sikadur-52 Injection, for example, up to 5 mm.
- Whether water is present. Epoxy resins for force-transmitting filling work in dry and damp cracks, but not in wet cracks or where water enters under pressure. If there is a leak, the water is first stopped with polyurethane resin or foam, and then the sealing task is addressed.
- What the temperature of the structure is during the work: viscosity and pot life depend on it. Resins with an extended pot life are produced for hot climates.
Materials
Epoxy resins for force-transmitting filling
Solvent-free two-component low-viscosity resins: they bond the faces of a crack so that in a pull-off test the concrete itself fails rather than the bond line, and they restore monolithic integrity. They are used for dormant cracks in columns, beams, slabs, foundations, walls and liquid-retaining structures. Important parameters are the viscosity at the working temperature, the pot life of a batch, the permissible moisture in the crack and the maximum crack width. Examples: Sikadur-52 Injection Normal and LP, Fosroc Nitofill EPLV, Epojet and Epojet LV made by Mapei.
Polyurethane and acrylate compounds
Elastic materials for sealing cracks and joints, including moving and damp ones, and for stopping water. They do not restore load-bearing capacity but reliably cut off the path of water. They are selected according to the presence and pressure of water and the movement of the crack.
Cementitious injection grouts
Microfine cement suspensions are used to fill large voids, honeycombing and cavities in mass concrete and masonry, where compatibility with the mineral substrate is important.
Procedure
- Survey: crack mapping, width and depth, movement (monitored with tell-tales where necessary), moisture.
- Preparation: the surface along the crack is cleaned of dust, laitance, efflorescence and coatings; the crack is blown out with oil-free compressed air.
- Packers: holes are drilled directly into the crack or at an angle from the adjacent concrete so that they intersect the crack plane, or surface ports are bonded on. The spacing is chosen so that the resin reaches the next packer; through-cracks are sealed on both sides.
- Sealing the crack mouth: the crack between the packers is sealed with epoxy putty, which is left to cure — otherwise the resin will escape.
- Injection: the resin is mixed in complete kits and pumped in, starting from the lowest packer of a vertical crack and working upwards, or from the end packer of a horizontal crack, until resin appears at the next packer; then the work moves on to the next one. Horizontal cracks can sometimes be filled by gravity.
- Completion: after curing, the packers are removed, the holes are filled and the surface seal is taken off.
- Inspection: resin consumption by section and, for critical structures, core sampling. Manufacturers require preliminary trials on a test area to check the suitability of the resin, the packer spacing, the equipment and the pressure.
Working in a hot climate
For Uzbekistan and neighbouring countries, this is a subject in its own right. The pot life of an epoxy resin shortens sharply as the temperature rises: the larger the batch and the hotter the weather, the faster the resin thickens in the container and in the pump hose. Manufacturers recommend mixing the resin in small batches and cooling the components before mixing, but not below +5 °C. Unmixed materials are stored somewhere cool, out of direct sunlight; the equipment — especially the parts in contact with the resin — is shaded; the work is moved to the cooler hours and carried out without interruption. Separate grades with an extended pot life are also produced for hot conditions, for example Sikadur-52 Injection LP. The pump and pressure are selected on a test area: the resin must pass through the crack to the next packer without blowing out the surface seal.
Common mistakes
- A rigid epoxy resin in a moving crack — the crack opens alongside.
- Epoxy resin in a wet crack or with water ingress — no bond to the crack faces.
- Viscosity too high for a narrow crack, or work in the cold — the resin does not reach the end of the crack.
- A large batch in hot weather — the resin thickens in the container and the hose before it can be pumped in.
- An uncured surface seal — the resin escapes to the surface and the crack is only partly filled.
- Thinning the resin with a solvent “to make it flow better” — manufacturers prohibit this.
- Injection without establishing the cause of the crack.
What to check with the supplier and the engineer
- the group to EN 1504-5 and the declaration of performance;
- the viscosity and pot life at the working temperature, the permissible moisture in the crack and the maximum crack width;
- the recommended packers, surface seal, pump and pressure;
- long-term strength taking creep into account, if the crack is in a load-bearing member;
- how to clean the equipment and the safety measures for working with resins.
Crack surveys and the choice of repair method are part of our engineering services; if strengthening is needed, see the “Strengthening with composites” section.
Materials in the catalogue
- Sikadur-52 Injection Normal — Sika — low-viscosity epoxy resin for structural injection of cracks up to 5 mm.
- Sikadur-52 Injection LP — Sika — long pot life epoxy resin for crack injection in hot weather.
- Fosroc Nitofill EPLV — Fosroc — low-viscosity epoxy resin for injecting 0.1–9 mm cracks in concrete.
- Epojet LV — Mapei — very low viscosity epoxy resin for injecting microcracks in concrete.
- Epojet — Mapei — solvent-free epoxy resin for crack injection and anchoring in concrete.
- Skrepa M600 Inyektsionnaya — Penetron — cement injection grout for cracks over 0.4 mm, voids and anchoring.
- Stabilcem — Mapei — expansive cement binder for injection and anchoring grouts and shrinkage-compensated concrete.
- Epojet SLV — Mapei — super-low-viscosity epoxy resin for injecting cracks, including damp ones.
This list is not exhaustive. Products for stopping water and for waterproofing injection are covered in the “Waterproofing” section.
Frequently asked questions
Which cracks can be injected with epoxy resin?
Dormant cracks that do not change in width, dry or damp without water ingress, within the width stated in the resin data sheet. For moving cracks and cracks with water, elastic polyurethane or acrylate compounds are used.
Does injection restore the strength of a structure?
Epoxy injection restores monolithic integrity and allows the structure to act as a single whole again. If the cracks were caused by insufficient load-bearing capacity, injection alone is not enough — a structural assessment and possibly strengthening are needed.
Can injection be carried out in winter?
Only within the temperature limits stated in the resin data sheet. In the cold, the resin thickens and cures more slowly; where necessary, the structure and the materials are heated.
What can cracks be sealed with on the surface if injection is not needed?
Fine dormant cracks in a surface that is to be protected are often covered with a crack-bridging protective coating or epoxy putty; the choice depends on the width, the movement and the appearance requirements.
We will select an injection resin and a method for your cracks — call us or message us on WhatsApp/Telegram: +998 94 094 52 27.