When concrete cracks due to structural movement, settlement, or lateral pressure, surface fillers alone won’t keep it stable. Crack stitching bars provide long-term reinforcement by tying both sides of the crack together. Installed into slots and bonded with epoxy grout, they restore tensile strength and prevent further separation. This guide explains exactly how to install crack stitching bars in concrete walls or slabs to permanently repair structural cracks.
Not all cracks need stitching. Look for long, wide, or recurring cracks (typically >3mm) across slabs or walls, particularly those with displacement or ongoing movement. If unsure whether the crack is active or the structure is safe, consult an engineer first. Stitching is used to reinforce — not replace — structural design or load-bearing capacity.
Mark out stitching slots perpendicular to the crack line, spaced 300–600 mm apart. For slabs, bars are typically 300–400 mm long; for masonry walls, longer 500–1000 mm bars may be used. Avoid placing them too close to slab edges or corners. The aim is to tie both sides of the crack together evenly with overlapping support.
Use a twin-blade wall chaser or angle grinder with vacuum extraction to cut slots into the concrete. Slot depth should be 25–40 mm (depending on bar size), and wide enough for grout coverage around the bar. Cut each slot across the crack, extending 150–200 mm past both sides. Clean out loose material with a brush and vacuum thoroughly.
Use a thixotropic epoxy grout or polyester resin mortar specifically designed for crack stitching. These bond tightly to concrete and bars without slumping. Mix according to manufacturer’s instructions. Wear gloves and use a mixing paddle or applicator cartridge. Don’t let the mix sit for too long — many have a working time of 20–40 minutes depending on temperature.
Use a pointing gun or trowel to press a 10–15 mm layer of grout into the bottom of the slot. Ensure full contact and no air pockets. If moisture is present in the slot, use a moisture-tolerant product. Don’t underfill — bars should sit fully embedded in the material, not touching raw concrete at the base.
Lay the stainless steel helical bar into the slot on top of the fresh grout. Press it gently into position along the centre line. Bars should not be kinked or bent into place — if a slot needs adjusting, cut it wider rather than forcing the bar. Ensure bars fully cross the crack by at least 100–150 mm each side.
Apply more grout over the bar to fill the slot fully. Use a trowel or pointing tool to compact the grout and smooth the surface flush. Avoid overfilling or leaving high spots — especially on polished or coated slabs. You can blend with surrounding texture later, or grind flush after curing if required.
Let the stitching bars and grout cure according to the product's instructions — typically 24 to 72 hours. Avoid loading the slab or wall during this period. Once cured, you can apply coatings, sealers, screeds, or even polished finishes over the area. Some repairs may require light sanding or grinding for a perfectly flush finish.
Crack stitching bars stabilise movement, but you may still want to seal visible hairlines for aesthetic or moisture reasons. Use a flexible crack sealant or coloured epoxy paste. Mark the date of repair and monitor the area for seasonal changes. If cracks reopen, further investigation may be needed — but with proper bar spacing and bonding, this is unlikely.
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