Structural cracks in concrete are serious — they weaken integrity, allow water ingress, and can worsen over time. When cracks are stable (not actively moving), injecting a two-part structural epoxy is one of the most effective ways to bond concrete back together permanently. This guide shows you exactly how to inject epoxy into structural cracks step-by-step using proper materials and technique.
Epoxy injection is only suitable for cracks in load-bearing concrete that are not actively moving. If the crack is growing, shrinking, or showing signs of thermal or moisture expansion, epoxy may re-crack once cured. Monitor over time if unsure. Measure width (typically 0.2–6 mm) and confirm both sides are still aligned. Active cracks may require flexible polyurethane injection instead.
Use a wire brush and vacuum to clean the crack surface thoroughly. Remove all dust, laitance, paint, sealers, or efflorescence. If the crack is accessible from the back, block it off using foam backer rod or tape to prevent epoxy from leaking out. For very tight cracks, flush out fine dust with compressed air. A clean, dry crack ensures proper epoxy penetration and bonding.
Surface ports are plastic nozzles glued directly over the crack using epoxy paste every 150–300 mm. For deeper injection, mechanical ports can be drilled and inserted at an angle to intercept the crack internally. Use epoxy paste to bond surface ports securely, and wait 30–60 minutes for the paste to cure. These ports will later allow controlled epoxy injection under pressure.
Once ports are installed, apply epoxy paste along the crack to seal the surface. This prevents epoxy from leaking out during injection. Feather the paste tightly against the crack edges using a putty knife, taking care not to clog the port openings. Allow this surface seal to fully cure before proceeding — typically 1–2 hours depending on the product and temperature.
Use a dual-cartridge injection gun loaded with two-part structural epoxy. Always purge a small amount first to ensure consistent mix at the nozzle. Starting from the lowest port (for vertical cracks), inject slowly until epoxy exits the next port up. Plug the lower port and move upward. For horizontal cracks, work from one end to the other. Don’t rush — allow epoxy to fill the entire depth.
Let the epoxy cure fully — typically 6 to 24 hours depending on the product and conditions. After curing, tap off or grind down ports and remove any surface seal paste. Clean and smooth the surface if it will be painted or coated. Once cured, the epoxy will have effectively fused the two sides of the crack into a monolithic structure again.
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