Pre Pour Slab Inspection

What we look for on a pre-pour inspection

A residential slab on a Brisbane or South East Queensland site is engineered for a specific soil class — typically M, H1 or H2 reactive clay across the Moreton Bay and Logan corridors. The reinforcement layout, edge beam depth, internal beam locations and concrete cover are all called up on the engineer's drawings, and small departures during the steel fix can compound into cracking, edge curl or termite vulnerability years later. Our pre-pour checklist works through each of these systematically:

• Formwork alignment and rigidity — set-out checked against the engineer's plan, bracing adequate to hold the perimeter under the load of wet concrete, no gaps where mortar could escape.
• Reinforcement steel placement — top and bottom mesh laps meet the minimum 225 mm overlap, edge beam cages have the correct number of bars and ligatures at the spacing called up, trench mesh is continuous around penetrations.
• Compliance with engineer's drawings — bar diameters and grades match the schedule, additional bars over internal beams or load points are present, any site-specific variations have been signed off by the engineer in writing.
• Soil compaction and base preparation — fill is properly compacted with no soft spots, sub-base is graded and clean, no organic material or loose spoil under the membrane.
• Plumbing penetration positions — sewer and waste penetrations match the hydraulic drawings to ±25 mm, sleeves are correctly sized so the slab is not loaded onto pipework, AS/NZS 3500 clearances around bends are respected.
• Termite barrier installation — perimeter and penetration system installed per AS 3660.1, joins lapped and sealed, no damage from later trades, manufacturer's installation requirements followed exactly so the warranty is enforceable.
• Concrete cover requirements per AS 3600 — bar chairs sized so the bottom mesh sits at the cover required for the exposure classification (typically 30–40 mm for residential slabs on grade in SEQ), chairs spaced close enough that the mesh does not sag below cover between supports.
• Vapour barrier and membrane — continuous under the slab, taped at all joins and penetrations, no tears from foot traffic during the steel fix.

Common defects we find at pre-pour

Most pre-pour inspections in Brisbane new builds turn up two or three rectifiable items. Builders run a lot of jobs in parallel and steel fixers move between sites quickly, so small things get missed. The most common items in our reports across the last twelve months are:

• Bar chairs spaced too far apart — mesh sags between supports and ends up with less than the required cover at the centre of the panel, the most common cause of corrosion-related cracking five to ten years post-pour.
• Missing ligatures in edge beams — the schedule calls for ligatures at 200 mm centres around penetrations and corners; in practice we frequently find one or two missing or spaced at 400 mm.
• Penetration sleeves out of position — most often the sewer stack is 30–80 mm off the hydraulic drawing because the plumber set out from a different reference point than the slab set-out.
• Termite barrier damage at penetrations — collars torn or displaced when conduit or pipework was installed after the barrier went down, breaking the continuous protected envelope.
• Inadequate cover at edge beams — bars too close to the side of the formwork, often because the cage was lifted and dropped during set-out. Once poured, these bars are vulnerable to moisture ingress at the slab edge.

Why timing matters: the 24–48 hour window

The pre-pour inspection has a tight window. Book too early and the steel fix is incomplete — penetrations not in, mesh not laid out, edge beam cages still loose. Book too late and the concrete truck is already on the way, leaving no time for the steel fixer to come back and correct anything we flag.

The sweet spot is 24 to 48 hours before the scheduled pour. By then the steel fix is finalised, the plumber and electrician have completed rough-in, the termite barrier is in place and the formwork is braced for pour. If we identify defects, the site supervisor has a full working day to coordinate corrections without pushing the pour date. We turn the report around the same day with photos and clear rectification recommendations so the conversation with the builder is fact-based, not adversarial.

Frequently asked questions