Frequently Asked Questions

What is the injection procedure for Conbextra EP10 when repairing a structural crack in a reinforced concrete beam and how are the injection ports spaced?

The injection procedure for Conbextra EP10 in a reinforced concrete beam crack follows a systematic sequence to ensure the crack is completely filled with epoxy resin from the deepest point to the surface without entrapping air pockets that would leave unfilled voids in the repaired crack. The full procedure is: crack mapping and assessment — before any injection work, map the crack fully on the beam surface (mark on a drawing or by photography), measure the crack width at multiple points, and assess whether the crack is dormant or active (place a tell-tale reference marker across the crack and observe for 2 to 4 weeks to confirm dormancy before injection); surface preparation — clean the crack surface of dust, loose concrete, and contamination using compressed air blowing (blow along the crack from one end); port installation — drill and fix injection ports (plastic nipple ports) into the crack at intervals of approximately 150 to 250 mm along the crack length; the port spacing depends on the crack width — for very fine hairline cracks (0.1 to 0.3 mm) use shorter spacing (150 mm) to ensure the low-viscosity resin can travel between ports through the tight crack; for wider cracks (0.5 to 3 mm) use 200 to 250 mm spacing; seal the crack surface between ports with a rapid-setting crack sealer (Fosroc Renderoc Plug or an epoxy crack sealer paste) to prevent resin bleeding to the surface between ports; allow the surface sealant to harden fully (typically 2 to 4 hours) before injection begins; mixing Conbextra EP10 — mix base and hardener in the correct ratio (as supplied) until a uniform colour and consistency is achieved (typically 3 minutes of thorough mixing); injection — for a horizontal beam soffit or vertical crack, begin injection from the lowest injection port (bottom of the crack or one end of a vertical crack); inject Conbextra EP10 at low pressure (2 to 4 bar maximum) until resin is seen flowing from the adjacent port — then seal the completed port and move to the next; continue port by port until the full crack length is injected; cure and finish — allow the injected resin to cure fully (24 hours at 25 degrees before removal of ports; 48 hours before the repair is subjected to loading); remove ports by cracking the plastic nipple with a hammer, and grind flush with the concrete surface.

What is the minimum and maximum crack width that Conbextra EP10 can be injected into and what alternative products should be used for cracks that are outside the Conbextra EP10 injection range?

Fosroc Conbextra EP10 is effective for injection into cracks in the range of approximately 0.1 mm to 3 mm width — below the 0.1 mm lower limit, the crack is too tight for even the very low-viscosity EP10 resin to penetrate under practical injection pressures without risk of exceeding the concrete tensile strength at the crack tip; above the 3 mm upper limit, the crack volume is too large for epoxy resin injection to be economical and a repair mortar fill or structural repair approach is more appropriate. For cracks below 0.1 mm: hairline cracks in concrete (typically 0.05 to 0.1 mm) are within the range where capillary action and gravity feed of very-low-viscosity epoxy or acrylic resin can be effective on horizontal surfaces; for vertical or overhead surfaces, these very fine cracks may need to be widened by crack chasing (routing a slot wider than the crack) and filled with a Fosroc flexible sealant rather than injected. For cracks in the 0.3 to 1.5 mm range: Conbextra EP10 is ideal — standard low-pressure injection technique achieves good penetration at this width. For cracks wider than 3 mm: the crack is generally better treated by routing and sealing with a flexible sealant if the crack is a movement crack (Thioflex 600, Nitoseal MS600), or by routing and filling with a rigid cement-based repair mortar (Renderoc S or Renderoc DS) if the crack is dormant and surface appearance restoration is the priority. For very wide cracks and voids (greater than 10 mm): Fosroc Nitofill Urethane Foam injection resin (expanding polyurethane) is appropriate for stopping active water infiltration, or Conbextra grout injection for large void filling.

Can Conbextra EP10 be injected into cracks in a basement wall that is actively leaking (water flowing through the crack) and is it effective as a water-stopping injection resin for wet concrete structures?

Fosroc Conbextra EP10 is NOT suitable for injection into actively leaking cracks in basement walls or any other concrete structure where water is actively flowing through the crack at the time of injection. The presence of flowing water in the crack prevents Conbextra EP10 from working correctly for two fundamental reasons: dilution and washout — as the low-viscosity epoxy resin is injected into the water-filled crack, the flowing water dilutes and displaces the resin before it can flow to fill the crack and cure; the resin is washed out of the crack by the water flow, leaving the crack unfilled; no cure in wet conditions — epoxy resins, including Conbextra EP10, require a dry or at least damp-dry substrate for cure; in a crack filled with flowing water, the water at the crack faces prevents the epoxy from curing fully against the wet concrete surface, and the water pressure from behind can displace the injected resin before it reaches adequate gel strength. For active water leaks in concrete basements and tunnels, the correct injection product is a hydrophilic polyurethane foam injection resin (such as Fosroc Nitofill Urethane Foam or equivalent) — hydrophilic PU foam reacts with and expands on contact with water, rapidly generating a high-volume closed-cell foam that fills the crack and creates mechanical water stoppage; the foam reaction is triggered by the water and continues even in the presence of flowing water, providing a temporary or permanent water stop within seconds to minutes of injection. After the active water leak has been stopped with PU foam injection, and after the structure has been dewatered and the concrete surface has been allowed to dry to a damp-dry condition, Conbextra EP10 can be injected alongside the foam-plugged zone to restore structural strength across the previously leaking crack — the two-stage approach (PU foam for water stop, then EP10 for structural restoration) is the correct sequence for wet structural crack repair.