How to Tie Reinforcing Mesh Correctly Before Pouring Concrete

Tying reinforcing mesh correctly is one of the most important steps before pouring a concrete driveway. Done right, it keeps the steel in the correct position within the slab, giving your concrete the tensile strength it needs to resist cracking under load and New Zealand's variable ground conditions. This guide walks you through the process in plain language so you can either do it yourself with confidence or know what to expect when a professional does it for you.

What Is Reinforcing Mesh and Why Does It Matter?

Reinforcing mesh (also called reo mesh or bar mesh) is a grid of steel rods welded together at regular intervals. When embedded in concrete, it helps the slab resist the tensile forces that cause cracking — especially important in driveways that carry vehicle loads. In New Zealand, residential concrete slabs are typically constructed to meet the requirements of the NZ Building Code and relevant standards. For driveways, the mesh grade, spacing, and cover depth all matter. If you're unsure what specification is required for your project, check with your local council or a qualified driveway layer.

Tools and Materials You'll Need

• Reinforcing mesh sheets (commonly SE62 or SE72 grade for residential driveways — confirm with your supplier or engineer)
• Tie wire (also called reo wire or annealed wire, typically 1.6 mm gauge)
• Wire tying pliers or a reo tying tool (a hook-style tool that twists the wire quickly)
• Bar chairs or mesh chairs (plastic or concrete spacers to hold the mesh at the correct height)
• Wire cutters or bolt cutters
• Safety gloves and eye protection

Step 1: Prepare Your Formwork and Sub-base

Before placing any mesh, make sure your formwork (the timber or steel edging that defines the slab shape) is correctly set and your compacted sub-base is ready. A well-compacted gravel sub-base is essential for a durable driveway. The sub-base should be firm, level, and free of soft spots.

Step 2: Place Bar Chairs for Correct Cover

This step is critical and often skipped by DIYers — with costly results. Concrete cover is the distance between the steel mesh and the bottom surface of the slab. For a residential driveway slab exposed to the ground, a minimum cover of 40 mm is a common requirement, but always confirm this with your local council or a licensed building practitioner, as requirements can vary.

Place bar chairs (plastic spacers) across the sub-base at roughly 600–800 mm centres in both directions. These hold the mesh up off the ground so it sits in the correct position within the slab rather than lying on the bottom where it provides little benefit.

Step 3: Lay the Mesh Sheets

Carry mesh sheets carefully — the cut ends are sharp. Wear gloves at all times. Lay the first sheet onto the bar chairs. Where sheets need to overlap (called a lap splice), overlap them by at least one full mesh square plus 25 mm — typically 225–250 mm for standard mesh. This overlap ensures the load transfers properly between sheets. Check your mesh supplier's datasheet or ask your council if you need a specific lap length for your project.

Step 4: Tie the Mesh at Overlaps and Intersections

This is where tying comes in. You don't need to tie every single intersection — focus on:

• Every intersection within the lap splice zones (where sheets overlap)
• Every second or third intersection across the rest of the sheet to keep it stable during the pour
• Any corners or edges where the mesh might shift

How to Tie a Reo Knot

1. Cut a piece of tie wire roughly 200–250 mm long.
2. Fold it in half to create a loop.
3. Pass the loop under the intersection of the two mesh bars (or the overlapping bars).
4. Thread the two free ends through the loop and pull snug.
5. Using your tying pliers or hook tool, grip the two free ends together and twist clockwise — typically 3–4 full twists until the wire is firm but not so tight it snaps.
6. Bend the twisted tail down flat so it won't poke up into the concrete surface.

The tie doesn't need to be structural — its job is simply to hold the mesh in position until the concrete is poured and sets. A firm, neat tie is all you need.

Step 5: Check Position Before Pouring

Walk the slab area carefully before the concrete truck arrives and check:

• Mesh is sitting on bar chairs and not resting on the ground
• Lap splices are correctly overlapped and tied
• No mesh is closer than 40 mm to any edge of the formwork (side cover)
• No sharp wire ends are pointing upward
• The mesh won't shift when workers walk on it during the pour

If the mesh sags between chairs, add more chairs or use a heavier chair. During the pour, have someone check the mesh isn't being pushed down by foot traffic — mesh lifters (hooks used to lift mesh during pouring) can help keep it in position.

When to Call a Professional

While placing and tying reo mesh is generally not restricted work under NZ law, getting it wrong can result in a slab that cracks prematurely or fails to meet the Building Code. For driveways over a certain size or complexity, a building consent may be required — always check with your local council first, as Schedule 1 exemptions have specific conditions. You can find more guidance at MBIE Building Performance.

If your driveway is on a slope, near a retaining wall, or needs to carry heavy loads (such as trucks or caravans), it's well worth getting an engineer's specification and hiring a qualified driveway layer. You can find experienced local professionals on tradedirectory.co.nz.

Safety note: Reinforcing mesh has very sharp cut ends. Always wear heavy-duty gloves and safety glasses when handling and cutting mesh. Keep the work area tidy to avoid trip hazards.

Sources & Further Reading

• MBIE Building Performance – Building Code and consents
• BRANZ – Concrete slab construction guidance
• Licensed Building Practitioners – Find a qualified professional
• WorkSafe NZ – Safe work on construction sites
• Standards NZ – NZ construction standards