Reinforcement mesh doesn’t just stop cracks — it controls shrinkage, adds load-bearing strength, and makes your slab last. But only if it’s installed right. If mesh lies on the bottom of the slab, or sinks into insulation, it’s doing nothing. This guide shows how to properly install steel reinforcement mesh in a concrete slab — including placement height, supports, tying, and lap lengths — the way it’s done on professional sites.
Reinforcement mesh comes in different grades depending on slab use. For domestic floors or extensions, A142 or A193 mesh is common. Heavier loads (like garages or driveways) may need A252. Check your engineer’s spec if one exists — or follow manufacturer slab tables based on thickness and span. Each mesh type has specific bar thickness and spacing, and directly affects strength, crack control, and cost.
Before mesh goes in, your slab base must be ready — whether that’s compacted hardcore, insulation boards, or DPM. Make sure the surface is flat, solid, and protected from moisture. If insulation is part of your build-up, you’ll need plastic chairs or spacers to support the mesh and prevent it sinking into the boards during the pour. Don’t lay mesh directly on insulation without supports — it defeats the point of reinforcement.
Mesh should sit around 30–50mm up from the base of the slab, roughly one-third of the total thickness. Use bar chairs, mesh spacers, or concrete blocks to lift it off the ground. Space chairs every 600–1000mm depending on slab thickness and mesh weight. They hold the mesh up during the pour, stopping it from sagging to the bottom — which is where mesh is useless. Don't rely on walking it up or raking it in later — it rarely works.
Mesh sheets should be overlapped by at least 350mm (or 2 full grid squares) to ensure full strength across joints. Lay the mesh so it’s flat, square to the slab, and not buckled or forced. If your slab needs two layers of mesh (top and bottom), they must be separated by spacers and fixed in place. Avoid walking on the mesh during layout — it can shift chairs and damage insulation.
Use steel tying wire or mesh clips to connect the overlapping sheets. Tie every 300–400mm around the perimeter and at the overlap edges. This prevents the mesh shifting during the pour and keeps the reinforcement consistent. Twisting ties with pliers or a tying tool keeps things tight and flush. For small pours, you can tie by hand — but larger slabs benefit from mesh fixers and walk-behind tools.
Edges of slabs are more prone to stress, so reinforce them properly. Ensure the mesh reaches close to the perimeter (usually 50mm cover) without being exposed. If needed, add extra bar or U-bars at slab corners or where thickenings occur. Watch for chairs that get knocked over near formwork — this is where mesh often sinks too low. Double-check support at all external edges and around service penetrations.
Once mesh is in place, use a laser or measuring stick to check the mesh is sitting at the correct depth — one-third from the base is typical. Reposition chairs or re-tie mesh if needed. Avoid relying on the pour to “float” the mesh — it will not. Everything should be stable, supported, and tied before concrete arrives. This is your last chance to make reinforcement effective — not cosmetic.
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