Reo (steel reinforcement) for residential concrete

TL;DR

Reo is the steel mesh or bar embedded in concrete to resist the tensile forces that plain concrete cannot handle. The engineer specifies the grade (mesh or bar), size, layout, lap lengths, and cover. Get those four things right before calling the certifier for the pre-pour inspection, because a failed inspection pushes your pour date and concrete bookings are not free to reschedule. The most common on-site failure is sagging mesh with insufficient cover: 30 mm to a membrane, 40 mm to bare ground, enforced by bar chairs at 800 mm centres per NCC 2022 ABCB Housing Provisions clause 4.2.11.

What it is

Reo (reinforcement) is steel embedded in concrete to carry tensile and bending loads. Plain concrete is strong in compression and weak in tension: add steel and the composite handles both. On residential jobs, reo comes in two main forms:

Mesh (welded wire fabric): pre-fabricated sheets of ribbed wire welded at intersections. Specified by grade designation (e.g. SL82, RL818) and laid in sheets with required laps.
Bar (deformed bar, rebar): individual straight bars of specified diameter (e.g. N12, N16, N20). Used in footings, beams, columns, and anywhere that mesh sheets cannot reach or where the engineer requires closer control.

Also known as: reinforcement, reinforcing steel, rebar (US term, seldom used in Australia).

All steel reo for Australian residential construction must comply with AS/NZS 4671:2019, Steel for the reinforcement of concrete (verified 2026-05-08).

Properties

Mesh (welded wire fabric) specifications per AS/NZS 4671

SL series: square mesh (equal spacing each way). RL series: rectangular mesh (closer spacing in the main direction). All sheets are approximately 2.4 m x 6 m. Data sourced from ACRS-certified Australian suppliers, compliant with AS/NZS 4671 (verified 2026-05-08).

SL series (square mesh):

Designation	Wire dia. (mm)	Spacing (mm)	Ast each way (mm²/m)	Sheet mass (kg)
SL62	6.0	200	141	33
SL72	6.75	200	179	41
SL82	7.6	200	227	52
SL92	8.6	200	290	66
SL102	9.5	200	354	80
SL81	7.6	100	454	105

RL series (rectangular mesh, main direction/cross direction):

Designation	Main wire (mm)	Main spacing (mm)	Cross wire (mm)	Cross spacing (mm)	Main Ast (mm²/m)	Cross Ast (mm²/m)	Sheet mass (kg)
RL718	6.75	100	7.6	200	358	227	67
RL818	7.6	100	7.6	200	454	227	79
RL918	8.6	100	7.6	200	581	227	93
RL1018	9.5	100	7.6	200	709	227	109

Deformed bar (N grade) specifications per AS/NZS 4671

ACRS-certified D500N grade (Deformed, 500 MPa yield, Normal ductility). Stock lengths 6 m, 9 m, 12 m. Data from ACRS-certified Australian suppliers, AS/NZS 4671 compliant (verified 2026-05-08).

Bar size	Nominal dia. (mm)	Mass (kg/m)
N10	10	0.66
N12	12	0.928
N16	16	1.649
N20	20	2.577
N24	24	3.711
N28	28	5.051
N32	32	6.597
N36	36	8.350

Residential footings and slabs typically use N12 to N20 bar. N12 and N16 are bent cold; N20 and above need a power bender.

Grades and variants

Type	Typical residential use
SL72 mesh	Light residential slab panels, paths, driveways (where engineer specifies)
SL82 mesh	Standard residential slab on ground, waffle pod slab infill
SL102 mesh	Heavier residential slabs, reactive soil sites (M, H, E class)
RL818 / RL918 mesh	One-way spanning slabs, suspended slabs, where main direction loading is dominant
N12 bar	Trench footings, tie-down bars, starter bars, fitments
N16 bar	Stiffened raft edge beams, columns, portal frames, medium footing beams
N20 bar	Heavily loaded beams and columns, high site-classification footings
Trench mesh (TM)	Strip footings and trench beams (200 mm, 300 mm, 400 mm wide; 3 to 5 bars at 8, 11, 12 or 16 mm dia.)

The engineer’s drawings specify the exact grade for each element. Never substitute a lighter grade without re-approval.

Where to use

Ground slabs (stiffened raft, conventional slab, waffle pod infill) per engineer’s details and AS 2870:2011
Pad footings and strip footings
Retaining wall stems and footings
Suspended slabs and stairs
Concrete columns and portal frames
Any concrete element where the design requires tensile capacity

Where NOT to use

Do not substitute grades. Replacing SL82 with SL72 because the merchant was out of stock is a structural defect. Phone the engineer first.
Do not lap short. Lap lengths are structural calculations, not a guide. Short laps fail in bending.
Do not use plain bar (R grade) where deformed bar (N grade) is specified. Bond strength is lower.
Do not place reo without bar chairs. Reo resting on the ground or on formwork delivers zero cover. It fails inspection and corrodes.
Do not use reo covered in rust scale, mud, concrete splatter, or oil. Light surface rust is acceptable; loose scale, mud, and grease reduce bond. Clean before pouring.

Fixing and installation

Concrete cover requirements (NCC 2022 ABCB Housing Provisions clause 4.2.11(5))

Cover is measured from the nearest concrete face to the nearest steel surface.

Exposure condition	Minimum cover
To a membrane in contact with ground	30 mm
To unprotected ground (no membrane)	40 mm
To internal surfaces (above ground, protected)	20 mm
To external exposure	40 mm

Source: NCC 2022 ABCB Housing Provisions Part 4.2, clause 4.2.11(5) (verified 2026-05-08).

Where AS 3600:2018 applies (engineer-designed elements), exposure classification governs: a Class A2 element in N25 concrete typically requires 30 mm cover. Always follow the engineer’s details; they may specify more than the NCC minimum (verified 2026-05-08).

Bar chair types and spacing

Bar chairs (reo chairs) lift mesh off the ground to achieve specified cover.

Chair type	Typical use
Plastic stools (25 mm, 30 mm, 40 mm, 50 mm heights)	Slabs on ground
Wire chairs	Slabs and beams (uncoated wire: confirm cover to the wire itself meets the requirement)
Concrete block spacers	Footings and heavy slabs

Spacing: Bar chairs at not more than 800 mm centres for steel fabric (NCC 2022 ABCB Housing Provisions clause 4.2.11(7)(e)) (verified 2026-05-08). Closer spacing (600 mm) is common practice to prevent sag in the middle of bays.

Select chair height to match the cover requirement plus wire/bar radius. A 30 mm chair under 7.6 mm wire gives approximately 34 mm to the top of the bar, which satisfies the 30 mm cover-to-membrane requirement.

Lap lengths for residential concrete (NCC 2022 ABCB Housing Provisions Table 4.2.11b)

Steel element	Minimum lap
Bars up to and including 12 mm diameter	500 mm
Bars greater than 12 mm up to and including 16 mm diameter	700 mm
Trench mesh	500 mm

Source: NCC 2022 ABCB Housing Provisions Part 4.2, Table 4.2.11b (verified 2026-05-08).

For engineer-designed elements under AS 3600:2018, development and lap splice lengths are calculated values, typically longer than the NCC deemed-to-satisfy minimums. Follow the structural drawings (verified 2026-05-08).

Concrete strength

NCC 2022 ABCB Housing Provisions requires concrete not less than N20 grade (20 MPa at 28 days) for footings and slabs under the deemed-to-satisfy path. Engineer-designed elements often specify N25 or N32 (verified 2026-05-08).

Permitted reo types (NCC 2022 ABCB HP clause 4.2.11(1))

Three forms are permitted under the deemed-to-satisfy path: welded wire reinforcing fabric (mesh), trench mesh, and deformed reinforcing bars. Plain (R grade) bar is permitted only where specified by the engineer (verified 2026-05-08).

Tolerances and acceptance

Numerical

Item	Limit	Source
Cover to membrane	30 mm minimum (NCC deemed-to-satisfy path)	NCC 2022 HP clause 4.2.11(5)
Cover to unprotected ground	40 mm minimum	NCC 2022 HP clause 4.2.11(5)
Bar chair spacing	800 mm maximum for mesh	NCC 2022 HP clause 4.2.11(7)(e)
Mesh sag mid-bay at pour (workmanship)	Per current HIA Guide to Materials and Workmanship. Verified numerical value pending HIA member access. [HIA-059]	HIA Guide / state guide
Bar position tolerance (engineer-designed elements, AS 3600)	Per AS 3600:2018 Section 4 and the structural drawings	AS 3600:2018

Visual acceptance at pre-pour inspection

The certifier’s pre-pour inspection checks, at minimum:

Mesh is on bar chairs, not resting on the ground or formwork
Cover matches the engineer’s details (measure at multiple points, not just corners)
Laps are at the correct length and staggered per the drawings
Edges and penetrations trimmed correctly (no reo crossing over slab boundaries without a construction joint)
Bar sizes, spacing, and layout match the structural drawings
No mud, oil, or concrete splatter on bars at bond zones
Mesh sheets tied at laps (not just resting)

Defects typical at PCI

Insufficient cover from sagging mesh between chairs (very common on thin slabs)
Short laps (pressure to save material; always a rejection)
Wrong mesh grade substituted without engineer sign-off
Bar chairs missing at penetrations and edges
Trench mesh or bars displaced after placing by trades walking on them without adequate protection

Working with other trades

Concretor: co-ordinates the pour. Reo must be correctly placed, inspected, and approved before concrete arrives. Walking on placed mesh without spreader boards risks displacement.
Certifier / building inspector: calls the pre-pour inspection. Do not pour before the pass is issued. Verbal approval is not enough; the written inspection notice is the record.
Structural engineer: specifies all reo. If the drawings and the NCC tables conflict, the drawings govern for any engineer-designed element.
Plumber / sparky: penetrations through slabs need sleeves that maintain reo continuity per the drawings. Cutting out reo to pass pipes is a structural defect.

Health and safety

Manual handling: an SL82 sheet (52 kg) requires two people to lift safely. SL81 sheets (105 kg) are a mechanical lift or require minimum three persons. Use sheet carrying clamps.
Sharp edges and cuts: cut bar ends and wire tails are a laceration risk. Wear cut-resistant gloves; bend or trim exposed tails before pedestrian access.
Working in excavations: when placing reo in trench footings, confirm trench wall stability and bench or batter as required before entry. HRCW in excavations > 1.5 m deep.
Concrete pour hazards: freshly poured concrete is alkaline and causes chemical burns on skin contact. PPE: gloves, eye protection, gumboots.

Suppliers

InfraBuild (infrabuild.com): largest Australian producer of reinforcing mesh and bar. ACRS certified.
ARC (Australian Reinforcing Company) (arcreo.com.au): mesh, bar, and trench mesh. ACRS certified.
BestBar (bestbar.com.au): mesh and deformed bar across all states.
Neumann Steel, OneSteel Reinforcing (InfraBuild group): major distributors in QLD and WA.

Trade pickup at steel merchants, concrete suppliers, building merchants with steel yards.

[Sponsor / preferred supplier slot. ACCC disclosure required.]

What can go wrong

Sagging mesh: bar chairs too far apart, or chairs knocked over during placing. Cover fails, steel corrodes over time, slab may crack along reo lines.
Short laps: cost-saving on site. Structural failure in bending at the lap. Rejected at inspection.
Wrong grade: SL72 installed instead of SL82. Inadequate tensile capacity. Engineer must assess and approve a fix; in a bad case, the slab is broken up.
Penetration errors: reo cut or displaced around plumbing penetrations. Stress concentrations at openings. Provide correctly detailed trimmer bars.
Mud contamination: chairs sink into wet subgrade, mesh drops to the ground. Re-chair before pouring.
Cover failures at edges: mesh carried to the slab edge without edge trim bars or dropped cover. Spalling at slab edge follows.
Unaccepted substitution: contractor orders a lighter mesh because the specified grade is on back-order and doesn’t tell the engineer. This is a contract defect and a potential structural defect.

References

AS/NZS 4671:2019, Steel for the reinforcement of concrete (Standards Australia) (verified 2026-05-08)
AS 3600:2018, Concrete structures (Standards Australia) (verified 2026-05-08)
AS 2870:2011, Residential slabs and footings (Standards Australia) (verified 2026-05-08)
NCC 2022 ABCB Housing Provisions Part 4.2, Footings, slabs and associated elements, clause 4.2.11 (ABCB) (verified 2026-05-08)
InfraBuild, Ribbed Square Mesh product data (infrabuild.com) (verified 2026-05-08)
BestBar, Deformed reinforcing bar product data (bestbar.com.au) (verified 2026-05-08)
Steel Reinforcement Institute of Australia (sria.com.au) (verified 2026-05-08)
CCAA (Cement, Concrete and Aggregates Australia), ccaa.com.au (verified 2026-05-08)