Frequently Asked Questions

What is the difference between crack stitching with Nitoplate Crackfix and crack injection for repairing a concrete crack?

Crack stitching and crack injection are two different approaches to structural crack repair and are appropriate for different crack types and structural objectives. Crack injection (using epoxy resin or polyurethane resin injected under pressure into the crack) fills the crack void with adhesive, restoring monolithic continuity through the crack plane when the injected resin cures. Injection is the right technique when the crack is relatively dormant (not actively growing or moving), when the crack is narrow enough to be injected (typically 0.2 to 3 mm width), and when the structural objective is to restore full tensile continuity through the thickness of the section. Crack stitching with Nitoplate Crackfix is appropriate when the crack is too wide or irregular for injection, when the crack is in masonry or poor-quality concrete where injection is impractical, or when the structural objective is to prevent further crack opening (arrest crack growth) rather than restore full tensile continuity. Stitching bars installed at angles to the crack act as ties holding the two sides of the crack together — if the crack subsequently moves thermally or under load, the stitching system restrains the opening rather than the injection resin fracturing again.

What slot dimensions and bar spacing are used for concrete crack stitching with Nitoplate Crackfix?

The slot for a stitch bar is typically routed across the crack at approximately 45 to 60 degrees to the crack direction — the angle is important because a bar at right angles to the crack provides maximum tensile restraint across the crack, while bars at 45 degrees also provide shear restraint. The slot width and depth must accommodate the stitch bar diameter plus a minimum epoxy cover around the bar (typically the slot is 10 mm wide and 30 mm deep for a 6 mm diameter stitch bar). The stitch bars are spaced at typically 100 to 200 mm centres across the crack depending on the structural forces being resisted and the crack length. The structural engineer specifying the crack stitching repair must determine the appropriate bar size, bar angle, and bar spacing based on the forces acting across the crack. After routing and cleaning the slot (with compressed air and a brush to remove all dust), the Nitoplate Crackfix epoxy is injected or pushed into the slot and the stitch bar embedded and aligned before the epoxy gels.

Can Nitoplate Crackfix be used for crack repair in a reinforced concrete water retaining structure?

Yes. Nitoplate Crackfix can be used for crack stitching in reinforced concrete water retaining structures such as tanks, reservoirs, sumps, and retaining walls holding water. The cured epoxy is chemically resistant to water and can be used in permanently submerged or wet crack conditions. However, the epoxy adhesive cannot be applied to a wet or actively leaking crack slot — the slot must be dry at the time of adhesive application for the epoxy to achieve the specified bond strength. For cracks in water retaining structures that are actively leaking water, the water flow must be stopped (using a hydraulic cement plug such as Fosroc Conbextra GP2 or a polyurethane injection resin to stop the leak) before the stitching slot is routed and the Nitoplate Crackfix epoxy is applied. For potable water contact applications, the epoxy must be confirmed as suitable for potable water contact — consult Space Arc Engineering for the specific product suitability confirmation.