Of all the decisions that go into a concrete construction project, the specification and placement of steel reinforcement is among the most structurally significant. Get it right and you have a durable, load-bearing element that will perform for decades. Get it wrong and the consequences range from cracking and excessive deflection to structural failure.
Seymour Building Supplies in Gladesville has been supplying Sydney builders, tradies and owner-builders since 1985. This guide covers the main reinforcement products, how concrete rebar and mesh are specified in Australia, and the accessories you need to get a reinforced concrete pour right.
Why Concrete Needs Reinforcement
Concrete is strong in compression but weak in tension. When a concrete element bends under load, one face is compressed (which concrete handles well) while the opposite face is stretched (which it doesn’t). Without reinforcement, the tension face cracks and the element can fail.
Steel reinforcement solves this by carrying the tensile forces the concrete can’t. The result, reinforced concrete, is far stronger in tension and far more ductile than plain concrete, so it can span, cantilever and carry loads that unreinforced concrete cannot.
That’s why steel reinforcement is used in virtually every structural concrete element, including footings, slabs on ground, suspended slabs, retaining walls, columns and beams.
Concrete Rebar and Reinforcement Products
Deformed Reinforcing Bar (Rebar)
Deformed reinforcing bar, commonly called rebar or reo bar, is the most widely used reinforcement product in Australian construction. Its ribbed surface creates a mechanical bond with the surrounding concrete, stopping the two materials from slipping relative to each other under load.
In Australia, rebar is manufactured to AS/NZS 4671. The everyday designation, such as N12, combines the ductility class with the bar size: “N” means a 500 MPa, normal-ductility deformed bar (D500N under the standard) and the number is the nominal diameter in millimetres.
Common sizes in residential and light commercial work include:
- N10 for lighter applications such as ligatures, starter bars and light masonry work.
- N12 for strip footings, slab edge beams and light structural elements. One of the most commonly specified sizes in residential construction.
- N16 for heavier footings, deeper retaining walls and suspended slabs.
- N20 and N24 for heavily loaded elements, more typical of commercial and civil construction.
The team at Seymour Building Supplies can help work out quantities for your job and talk through cut lengths and bending requirements.
Reinforcing Mesh
Reinforcing mesh is a factory-made sheet of steel bars welded together at set spacings, used where a uniform reinforcement pattern is needed across a large area. It’s the standard reinforcement for residential slabs on ground, driveways, paths and many commercial floors.
Common mesh types in Australia include:
- SL72 square mesh (6.75mm bars at 200mm centres), commonly specified for residential slabs on ground designed to AS 2870 Residential slabs and footings.
- SL82 square mesh (7.6mm bars at 200mm centres), used where more steel is needed than SL72 provides, such as stiffened raft slabs on more reactive sites or garage slabs.
- RL918 and RL1218 rectangular meshes, which have heavier main bars and are used in structural applications with greater reinforcement demands.
- Trench mesh (for example L11TM and L12TM), narrow strips of mesh used in strip footings and slab edge beams.
Mesh is much faster to install than individually tied bars and reduces the risk of placement errors on large slab pours. Adjacent sheets must be lapped at the joints, typically so the two outermost cross-wires of each sheet overlap, to keep the reinforcement continuous across the slab. Your engineer’s drawings or AS 2870 will set out the mesh type and lap details for your site classification.
Bar Chairs and Concrete Cover
Getting the right concrete cover over the reinforcement is one of the most important, and most frequently overlooked, parts of reinforced concrete work. Cover is the depth of concrete between the surface of the steel and the outside face of the element.
Adequate cover matters for three reasons. It protects the steel from corrosion by keeping moisture, carbonation and chlorides away from it, it gives the bar enough surrounding concrete to develop a proper bond, and it contributes to the element’s fire resistance. The minimum cover depends on the exposure classification and the element type, as set out in AS 3600 (and AS 2870 for residential slabs and footings).
Bar chairs are plastic or wire supports that hold the reinforcement at the correct height above the formwork or ground during the pour, so the specified cover is achieved throughout. Bar chairs come in a range of heights to suit different cover requirements; ask the team which height suits your job.
Tie Wire
Tie wire secures intersecting bars and mesh sheets at their junctions, holding the reinforcement in place while concrete is placed and vibrated. The trade standard is 1.57mm annealed wire (often called 1.6mm), available in black or galvanised, and a roll or belt pack with a tying tool is a staple on every reinforced concrete job.
For lintels, T-bars and how reinforcement fits into masonry openings, see our guide to lintels for brickwork and reinforced concrete materials.
Additional Concrete Materials at Seymour Building Supplies
Alongside steel reinforcement, Seymour Building Supplies stocks the cement and concrete products needed to finish a reinforced concrete project.
General purpose and blended cements, rapid-setting products, bagged concrete mixes and specialty products from Boral, Sika, Mapei and Drizoro are available in quantities from a single bag to a full pallet, with same-day delivery Monday to Saturday across the Sydney metropolitan area. See the range on our Cements & Dry Mixes page.
Get Expert Advice on Your Reinforcement
The experienced team at Seymour Building Supplies can help with reinforcement for common residential applications, including bar size, spacing, cover and lap lengths for your type of project. For engineered or complex structural elements, the reinforcement specification should always come from a qualified structural engineer.
To discuss your reinforcement and concrete material requirements and arrange delivery to your Sydney site, visit the Seymour Building Supplies building supplies page or call the team on (02) 9816 5999. Located at 327 Victoria Rd, Gladesville.
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