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Concrete Pump / Reach 05 of 06

Reach 05 · Curing

Curing a house slab: what the NCC says

For a house slab built to the NCC’s Housing Provisions outside South Australia, the slab surfaces, including the edges, are moist cured for 7 days, and no stacked materials or building plant go on the slab for at least 7 days after pouring. The same clause sets the concrete’s grade and slump, rules out adding water beyond that slump, and, outside South Australia, stops a pour above 32ºC unless written instructions from a Professional Engineer are followed.

General information, not engineering advice. Your approved plans, engineer and certifier set what applies to your slab; the NCC itself is published on the ABCB’s site.

On this page The concrete clause, line by line · From the truck to the first week · Where the Housing Provisions stop · Wet concrete and skin

Clause 4.2.10

The concrete clause, line by line

For houses, the NCC accepts footings and slabs built to AS 2870, to AS 3600 or, within limits, to Section 4 of the ABCB Housing Provisions. In the Housing Provisions, clause 4.2.10 covers the concrete itself. It reads the same in the 2022 and 2025 editions of the NCC. On the left, the clause’s words; on the right, what they mean in plain terms.

  1. “Concrete must be manufactured to comply with AS 3600”
    The concrete itself must meet AS 3600; the clause points to that standard rather than repeating it.
  2. “have a strength at 28 days of not less than 20 MPa (denoted as N20 grade)”
    N20 is the strength the concrete must reach 28 days after pouring, not on the day it goes in.
  3. “have a 20 mm maximum nominal aggregate size; and have a nominal 100 mm slump.”
    Two more fixed numbers. Queensland’s concrete pumping code suggests checking the delivery document against what was ordered.
  4. “Water must not be added to the mix to increase the slump to a value in excess of that specified.”
    Adding water on site to raise the slump above what was specified is ruled out.
  5. “Concrete must be placed, compacted and cured in accordance with good building practice.”
    The NCC’s explanatory note says vibration removes air pockets and works concrete around the reinforcement, service penetrations and into formwork corners, for durability and resistance to termites and salt damp, and warns against over-vibrating.
  6. “Concrete in slabs must be adequately compacted, and slab surfaces, including edges, moist cured for 7 days.”
    Seven days of moist curing, for the surfaces and the edges alike.
  7. “After vertical surfaces are stripped of formwork, slab edges must be finished prior to curing.”
    The note explains that a finished and cured edge resists edge dampness better.
  8. “Loading of concrete slabs with stacked materials or building plant must not occur for a minimum of 7 days after pouring”
    For the first week, nothing stacked and no building plant on the slab. The clause still allows wall frames to be built and brickwork set out in that time.
  9. “Concrete must not be poured if the air temperature on site exceeds 32ºC unless written instructions from a Professional Engineer are followed.”
    A hot day changes the plan for the slab as well as for the crew. Heat and the pour.
Note · South Australia

South Australia replaces this clause with its own version in the NCC. SA’s version keeps the grade, aggregate size and slump, the ban on adding water and the call for good building practice, but leaves out the 7 days of moist curing, finishing slab edges before curing, the 7-day loading limit and the 32ºC rule. If the house is in SA, read the SA version.

On the day

From the truck to the first week

  1. Within one and a half hours

    The NCC’s explanatory note says the truck should be fully discharged within one and a half hours of the concrete first being mixed with water, unless a suitable retarder has been specified.

  2. During the pour

    Compacted, with no water added beyond the specified slump.

  3. Formwork off

    Slab edges finished before curing.

  4. Days 1 to 7

    Outside South Australia, surfaces and edges moist cured; no stacked materials or building plant on the slab.

  5. Day 28

    The day the N20 strength is measured against.

The clause asks for moist curing and leaves the method to good building practice. Your builder, engineer or plans may specify how it is done.

Where it stops

Where the Housing Provisions stop

The Housing Provisions are written for ordinary sites. If a site is classified as highly or extremely reactive clay, or as a problem site, they send the design to AS 2870 instead, and a moderately reactive site with deep-seated movement (class M-D) is beyond their scope too. In NSW, Section 4 of the Housing Provisions can be used only where the NCC’s NSW conditions are met.

A slab designed to AS 2870 or AS 3600 instead follows that standard, so the plans approved for the house are the place to check first.

On skin

Wet concrete and skin

Contact dermatitis is skin that becomes inflamed because of something that touched it: dry, red, painful, itchy, sometimes split, peeling, stinging or blistered. It mostly affects the hands, and it can take many months to heal. Safe Work Australia says sweating, heat and dust can make it worse.

Its controls for wet concrete on a pumping job are practical: somewhere to wash skin that gets concrete on it, taking off shoes and clothes straight after working with wet concrete, and gloves, safety goggles and waterproof footwear. Queensland’s concrete pumping code lists rubber safety boots among the protective equipment required when pumping, and a first aid kit with eye wash and protective creams on the pump unit.

Where to check Part 4.2 of the Housing Provisions on the ABCB’s NCC site, the plans approved for your house, and your certifier.