How we supply it: Binding wire is arranged through a partner hardware supplier who quotes, supplies and bills it and pays us a referral commission. TMT bars come from our own stock yards at factory-direct wholesale prices, so the wire can be loaded with the bars and arrive in the same trip.
In one line: Binding wire is soft, annealed mild-steel wire used to tie reinforcement bars together at their crossings so the cage holds its shape while concrete is poured.
What binding wire does, and what it does not
Binding wire is soft, annealed mild-steel wire used to tie reinforcement bars together at their crossings so the cage holds its shape while concrete is poured. It adds no strength to the finished member, and structural design ignores it.
Annealing makes the wire soft enough to twist by hand with a hook without snapping. Black annealed wire is commonly made to IS 280, the standard for mild steel wire for general engineering.
Gauges and finishes
| Gauge (SWG) | Diameter | Typical use |
|---|---|---|
| 16 | 1.6 mm | Heavy cages, large footings, column starter bars |
| 18 | 1.2 mm | General slab, beam and column work |
| 20 | 0.9 mm | Slab mesh with thin bars, faster tying |
| 22 | 0.7 mm | Light fabrication; too thin for most RCC |
Black annealed or GI wire?
| Point | Black annealed | GI (zinc-coated) |
|---|---|---|
| Twisting by hand | Easy, soft | Stiffer |
| Rust while the cage waits | Rusts within days in wet weather | Resists for weeks |
| Once cast in concrete with full cover | Performs fine | Performs fine |
| Cost | Lower | Higher |
How much wire per tonne of steel
Typical estimate: used by site engineers: 8 to 13 kg of wire per tonne of reinforcement. Thin bars mean more crossings per tonne, so they sit at the top of the range.
To work it out yourself: 1 kg of 18 gauge is about 109 m (9.2 g per metre), enough for roughly 360 ties at 30 cm each. One kg of 20 gauge is about 194 m.
- 8–10 kg per tonne where 12–20 mm bars dominate: footings, columns, beams
- 10–13 kg per tonne for slabs and walls with 8–10 mm bars at close spacing
- A house of 1,000 sq ft built-up area at a typical 3.5–4 kg of steel per sq ft uses about 3.5–4 tonnes of TMT and roughly 35–50 kg of wire
Five checks on wire coils
- Gauge two or three coils with a wire gauge or vernier: 18 SWG should read about 1.2 mm.
- Bend a short length back and forth; annealed wire bends easily and does not crack at the bend.
- Look at the surface: a dull tarnish is normal, flaking rust or pitting is not.
- Weigh the coils against the bill, since wire is sold by weight.
- Confirm black or GI as ordered: dull black versus bright grey.
Storing coils on site
- Keep coils on a pallet under cover; near the coast, black wire left in the open rusts quickly.
- Store them beside the TMT stack so the bar benders draw from one place.
- Cut only the day's lengths; pre-cut bundles left out rust at the cut ends.
- Sweep up offcuts every evening.
Tying mistakes that show up later
- Leaving wire tails pointing down into the slab's cover zone, where they rust and stain the ceiling.
- Using extra wire in place of proper laps or bar chairs.
- Tying only every other crossing at slab edges and around openings, where the mesh needs it most.
- Buying 22 gauge to save weight; it snaps when the cage is walked on.
- Pouring with loose wire offcuts still lying in the formwork.