Most domestic concrete slabs are reinforced with steel mesh — but sometimes, rebar is necessary. Whether it’s for structural loads, deep pads, footings, or to reinforce thickened edges, rebar gives concrete tensile strength where mesh can’t reach. This guide breaks down when rebar is needed, how to position it, and how to tie it off so it actually performs. If you're pouring a serious slab, this is the reinforcement method that holds everything together.
Rebar placement and thickness isn’t guesswork. Structural engineers specify the diameter (usually 10mm–20mm), spacing, and placement height depending on load, span, and soil conditions. If no spec is available, use a basic slab reinforcement guide: light-duty slabs may only need mesh, but anything over 150mm thick, heavily loaded, or on poor soil usually benefits from rebar — especially at thickened slab edges or beams.
Rebar must sit suspended within the slab — not resting on the ground. Use plastic bar chairs, concrete pads, or rebar spacers to hold it off the base. The typical cover (distance between rebar and edge of concrete) is 40–75mm depending on slab exposure and environment. Make sure chairs are stable and spaced every 600–1000mm. For slabs with double layers, use rebar supports to hold the top and bottom grids apart.
Where rebar crosses or overlaps, tie it securely using steel tying wire. Use pliers or a tying tool to create snug but not overly tight knots — the goal is to hold bars in position during the pour, not lock them permanently. Tying every second or third crossing is often sufficient. For mats or grids, create uniform spacing as per spec — e.g. 200mm centres — and check regularly with a tape to avoid drift or wide gaps.
Rebar can’t just stop and start — it must overlap at joins. The typical lap length is 40x the bar diameter (e.g. 400mm for 10mm bar). At corners, use L-shaped or U-bars to maintain continuity around edges. Always ensure laps are tied properly and supported — you don’t want bar lengths floating loose during the pour. Don’t weld rebar on site unless spec’d — tying is standard.
Any pipes, ducts, or voids in the slab weaken reinforcement — so rebar must go around them cleanly. Create frames or loops around service penetrations and tie into the main grid. For slab edges or beam thickenings, add extra bar or cages as needed, based on your design. Exposed or stressed corners are common crack zones — double up reinforcement in these areas where possible.
Before concrete arrives, measure the rebar depth (cover) from the surface and sides — this is key for durability. All bar should remain inside the concrete after curing, with no pieces exposed or touching formwork. Check for movement, tie any loose intersections, and confirm chairs are upright. Once you pour, rebar needs to stay exactly where it is — no shifting, bouncing, or floating. From here, the concrete will do the rest.
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