What to Look For in Your Pre-Pour Slab Inspection — A Queensland Homeowner's Guide

Why the Pre-Pour is Non-Negotiable

Your slab does three things: 1. Supports the entire weight of your home 2. Distributes that weight into the ground 3. Keeps water and termites out from underneath

If any of those three fail, the fix is enormous — cracked walls, sticking doors, failed waterproofing, termite invasion, and in the worst cases, the slab itself needs to come out.

Australian residential slabs are engineered to AS 2870 (Residential slabs and footings). Every part of your slab — the fill compaction, the reinforcement placement, the concrete strength, the termite barrier — is specified by that standard and by your engineer's site-specific design.

Builders work fast. Concrete gets ordered days in advance. The pressure to pour on the scheduled day is huge. That's when corners get cut. Your job (and mine) is to catch it before the truck rolls in.

1. Site Preparation — Has the Site Been Prepared Correctly?

Before anything else, the ground under your slab must be right.

What to check: - Site scraped and stripped to the correct reduced level. Your engineer's drawings specify the exact pad level (in metres above sea level) for your build. Ask the builder to show you the survey peg confirming the level. - All topsoil, vegetation and organic material removed to a minimum 150 mm depth — organic material rots and causes settlement. - Subgrade proof-rolled to reveal soft spots — soft spots must be removed and backfilled with engineered fill. - Natural subgrade compacted to minimum 70% density index (tested per AS 3798). - Cut and fill lines confirmed on site matching structural drawings.

Site-specific compliance (verify per AS 2870 Cl. 5.3): - No water ponding in trenches or on prepared subgrade - Site graded to a uniform fall of minimum 50 mm away from the building over the first metre (Appendix B2.3)

Red flag: Standing water on the pad the day before the pour. Water in trenches or in pod pockets. That water either evaporates and leaves voids, or gets poured into the concrete and weakens it.

2. Fill Material — What's Under Your Slab?

If your site is on cut and fill (most SEQ residential blocks are), the quality of the fill matters as much as the concrete on top.

What to check: - Fill material has minimum CBR value of 15% (California Bearing Ratio — a measure of fill strength) - Compaction tests completed on each layer — get copies of the test reports - Sand fill compacted to minimum 7 blows per 300 mm DCP reading (AS 1289.F3.3) - Controlled fill extends minimum 1 metre past the edge of the footing beam and battered back at maximum 1:2 slope

Red flag: Fill placed in a single lift without layered compaction testing. Uncontrolled fill = differential settlement = cracked walls in 2-5 years.

How to verify: Ask your builder for the compaction test reports before pour day. If they don't have them, don't accept "the geotech guy verified it verbally". You need the paperwork.

3. Formwork — Is the Slab Shape Right?

Formwork is the timber or steel edge that holds the concrete in place. Get it wrong and your slab is the wrong size, wrong shape, or wrong depth.

What to check: - Formwork set out matches the foundation plan — measure the outside dimensions with a tape - Edge beam width: minimum 310 mm external edge beam (per waffle raft design summary) - Garage edge beam width: 440 mm with garage door rebate 350 mm wide × 15 mm deep (verify against Sheet F5 or your engineer's garage detail) - Formwork lines straight and true — no bowing or misalignment (AS 3610) - Formwork heights match your slab depth specification — typical waffle raft is 400 mm overall with 100 mm top slab thickness - Step-downs in correct locations for showers (typically 70 mm set down) and garages - Ramp rebates at garage doors — 350 mm wide × 15 mm deep - All formwork braced and secured — won't move under concrete pour loads (AS 3610)

Red flag: Formwork that flexes when you push on it. When the concrete goes in, it'll bulge or move.

4. Waffle Pods — The Foam Blocks Under Your Slab

Modern residential slabs in QLD are often "waffle rafts" — a grid of foam pods with concrete ribs between them, topped by a thin concrete slab.

What to check: - Waffle pods are the correct depth: typically 300 mm main pods throughout, 225 mm pods at shower recesses - Pod layout matches the foundation plan at 1200 mm rib spacing - Start pod positions correct per the foundation plan - All pods seated correctly on prepared sand bed — no rocking or displacement - Pod edges clean — no mortar or debris bridging between pods and formwork (bridges = concrete short-circuits that reduce beam capacity) - Re-entrant steel installed at all internal corners — typically 3-L11TM 2000 mm long

What is re-entrant steel? Concrete cracks at internal corners because that's where stress concentrates. Re-entrant bars are extra reinforcement placed at 45° across those corners to stop cracks propagating.

Red flag: Missing re-entrant steel at any internal corner (L-shaped rooms, courtyards, etc). This is one of the most commonly missed items and it causes visible slab cracking within 2-3 years.

5. Reinforcement — The Top Slab Fabric

The top slab has a layer of steel mesh in it. This mesh is what keeps small cracks small.

What to check: - SL92 fabric confirmed throughout the top slab (no substitution — SL72 or SL62 are cheaper but weaker) - Fabric laps minimum 225 mm overlap of transverse bars at all edges - Fabric supported on chairs — with 25 mm top cover maintained (AS 3600) - Bottom fabric in position with correct cover — 40 mm bottom cover to external footings - Fabric free of rust, mud and contaminants prior to pour (AS/NZS 4671)

Rust on the mesh is OK if it's light surface rust and the bars are still full diameter. Heavy scale, pitting, or delamination is not OK.

Red flag: Mesh sitting directly on the pods or on the vapour barrier without chairs — that means zero cover, and the mesh will corrode within years.

6. Reinforcement — Edge Beam Steel

The edge beam (the perimeter of your slab) does the heavy lifting. It's where the walls will sit.

What to check: - Bottom reinforcement: 2 × 3-L11TM trench mesh OR 3-N16 alternative - Top reinforcement: 2-N16 continuous (clad) - Trench mesh laps minimum 500 mm at all splices - L-bars at all beam intersections with 500 mm laps to each leg - Outside corner lap bars: 1-N16 at all external footing beam corners

Verify all bar sizes on the engineer's drawings — some designs use different sizes based on wind classification or loads.

Red flag: Bars that end at a corner without a proper lap. The corner will be weak.

7. Reinforcement — Internal Rib Steel

Between the waffle pods, concrete ribs form a grid of small beams. Each rib needs its own steel.

What to check: - Each internal rib has 1-N16 bottom reinforcement - Internal rib width minimum 110 mm - All bar chairs at correct spacing — maximum 600 mm for fabric, 900 mm for bars 16 mm and greater (AS 3600)

Red flag: Any bar cut on site to clear a penetration. Bars can be displaced slightly to clear pipes, but not cut. If you see a cut bar, insist on additional reinforcement across that area.

8. Piers — For Deeper Foundations

If your soil is soft or reactive, your engineer may specify bored concrete piers to reach stable ground.

What to check: - 350 mm bored concrete piers at all locations marked on foundation plan (usually black dots) - Pier depth: founded minimum 300 mm into natural ground through any new rolled fill - Pier starter bars correctly positioned and at correct embedment depth - N16 additional top steel — 1 metre each direction over fill pier locations

Red flag: Piers that "hit refusal" too shallow. The engineer specifies depth for a reason — usually to reach a bearing stratum. If piers are shallower than the spec, get the engineer to confirm in writing before pour.

9. Ground Beams — Heavy-Duty Slab Beams

For larger homes or homes on reactive soils, your engineer may specify ground beams (called ST1, ST2 etc) — deeper, wider beams within the slab.

What to check (typical ST1 ground beam): - Location per foundation plan - Ground beam depth: 600 mm and width 350 mm - 3-bar top and 6-bar bottom reinforcement at ST1 locations - Beam reinforcement: 3-L12TM top and bottom with R10 ligatures at 600 mm centres - R10 starters at 600 mm centres in ST1 beams

Red flag: Ground beams built to standard edge-beam dimensions when the engineer specified deeper — this is a common builder cost-cut. Measure them.

10. Vapour Barrier — Keeping Moisture Out

Beneath your slab is a 0.2 mm polythene vapour barrier. This stops ground moisture from wicking up through the concrete into your floors.

What to check: - 0.2 mm thick vapour barrier installed across the full slab area (AS 2870) - Joints lapped and taped — no gaps or tears - Vapour barrier turned up at edges — not punctured by reinforcement chairs - Pipe penetrations sealed with closed cell polyethylene lagging or equivalent - 50 mm minimum sand bed under the membrane

Red flag: Tears, unsealed penetrations, or membrane punctured by reinforcement chairs. Once concrete covers it, moisture will find every hole.

Simple test: stand on the vapour barrier before the pour. Any rip you see under your boots is a rip that lets moisture in forever.

11. Drains — What's Cast Into the Slab

In Queensland this slab-stage plumbing is called "drains", not "rough-in" — the rough-in comes later, in the wall frame. Every drain, waste pipe, water pipe and electrical conduit that runs through your slab must be in place BEFORE the pour.

What to check: - All under-slab drainage pipes in correct positions matching the slab plan - All pipe penetrations sleeved through edge beams using closed cell polyethylene lagging - Conduits for kitchen island bench services in position (a common miss — hard to add later) - No penetrations, chases or embeds exceeding 150 mm diameter other than those shown on structural drawings - Cast-in conduits: minimum clear spacing of twice the larger conduit diameter from parallel reinforcement

Red flag: Any plumbing "we'll add that after". No you won't. Once the slab is poured, adding a drain means demo work.

Ask your plumber for their as-built diagram showing every pipe and conduit position. Cross-check against your kitchen and bathroom fit-out designs.

12. Termite Barrier — Non-Negotiable

Every new home in QLD must have a termite management system installed before the slab is poured (AS 3660.1:2014 / NCC).

What to check: - Termite barrier system installed and continuous under all slab perimeters - Barrier not damaged or punctured by services installation - If it's a chemical barrier: spray records dated + applicator certificate - If it's a physical barrier (like Kordon or Termimesh): installer's compliance certificate on site - Physical barrier installed at all pipe penetrations and slab edges — no gaps

Red flag: No visible physical barrier at pipe penetrations. Termites will find that gap in year one and you'll spend $15,000+ dealing with it.

13. Concrete Mix — What's Actually Getting Poured

The truck arrives with a docket. That docket tells you what mix is in it.

What to check on the docket: - Concrete grade matching the engineer's specification — typically N25 or N32 for a residential slab on ground. There is no single "minimum" number; the docket must match the grade your engineer specified for this slab, not a generic figure. - Footing/edge-beam concrete grade matching the engineer's specification - Slump 80 mm ± 10 mm (verified on delivery — the batcher can add water on site to hit this, but too much water = weak concrete) - Maximum aggregate size 20 mm - No calcium chloride in the mix - No admixtures without written engineer approval

Red flag: A slump test that comes in over 100 mm or under 60 mm. Ask them to reject the load — the batch plant is 15 minutes away.

14. Pour Day — Placement, Vibration, Curing

Getting the concrete on site is only half the job.

What to check: - Concrete mechanically vibrated in place (a poker vibrator is on site and being used) - Concrete in all beams mechanically vibrated — not just the top slab (AS 2870 Cl. H2) - Curing method confirmed and ready — either curing compound sprayed on within an hour of finish, or wet burlap covering the slab for 7 days - Saw joints cut within 8 hours of pour (within 4 hours if temperature exceeds 32°C)

Red flag: No vibrator on site. Concrete without vibration has honeycombing and weak zones you'll never see.

During finishing: - No water added to the surface during finishing (a common bad practice that weakens the top layer) - Steel trowel finish only after bleed water has evaporated

15. Site Access and Setup

Overlooked stuff that can turn a pour day into a disaster.

What to check the day before: - Concrete truck access — is the driveway suitable for a 25-tonne truck? Any overhead wires? - Concrete pump availability — if the pour needs a pump, is it booked? - Property boundary setback — measure the slab position against title boundaries. Setback is a legal requirement. - Downpipe / stormwater tie-ins — any drainage that must be installed BEFORE the pour? Check your civil drawings. - Neighbour notification — for boundary walls or shared access, has the neighbour been notified? (Not legally required but good practice) - Weather forecast — check the 24-hour forecast. Pouring in heavy rain is a disaster. Pouring in 38°C heat needs extra planning.

Red flag: Rain forecast for the day of the pour and the builder wants to proceed anyway. Rain during the pour dilutes the surface concrete. Push for a reschedule.

16. Documentation On Site

If the paperwork isn't right, nothing else is right.

Must be on site the day of the pour: 1. Foundation plan — current revision, matching what's being built 2. Structural engineering drawings — current revision, all sheets 3. Architectural working drawings — current revision 4. Termite treatment certificate or physical barrier installer's certificate 5. Under-slab drains signed off by a licensed plumber 6. Compaction test results for the fill 7. Surveyor / engineer setout confirmation — pre-pour setout confirmed 8. Truss manufacturer's plan confirming internal load-bearing wall positions (so the reinforcement matches)

Red flag: Any missing document. Especially the termite certificate — that one is a legal requirement.

17. Post-Pour — What Happens After

Your job doesn't end when the concrete lands.

Within 8 hours of pour: - Saw joints cut (crack control) - Curing compound applied OR wet burlap covering

Days 1-7 after pour: - Slab kept moist for minimum 7 days for proper strength development - No load on the slab for 24 hours minimum (walking traffic only after 24 hours) - Full loads (framing crew) after 7 days - Concrete cylinder test results — the batcher takes samples; ask for the 7-day and 28-day break test results

Red flag: Slab left to dry in the sun with no curing compound. The top surface loses strength permanently.

The 15 Red Flags — Call an Inspector If You See Any of These

If any of these are present the day before or during your pour, book an independent inspection immediately:

1. Standing water in trenches, on pods, or on the pad 2. Rusty or damaged mesh with heavy scale or pitting 3. Missing re-entrant steel at any internal corner 4. Mesh sitting directly on pods or vapour barrier with no chairs (no cover) 5. Torn or unsealed vapour barrier 6. Fill placed without compaction test results 7. Waffle pods rocking or unseated on the sand bed 8. Bars cut on site to clear penetrations (not just displaced) 9. Formwork that flexes when pushed 10. Missing termite barrier or damaged during installation 11. Missing compaction test reports for the fill 12. Concrete docket showing a grade below the engineer's spec (not the N25/N32 the engineer nominated) 13. No vibrator on site for the pour 14. Rain forecast > 5 mm on pour day and builder wants to proceed 15. Missing plumbing rough-in (drains, water, conduits) at fit-out positions

Any one of these = call an inspector. Three or more = stop the pour.

What VG Inspect Checks on Every Pre-Pour Slab Inspection

I run through this exact list on every pre-pour inspection. Same day report with photos of every finding cross-referenced to your engineer's drawings.

What you get: - Written builder action list — clear rectification steps, not just complaints - Photos of every defect with location - Reference to specific AS/NZS standards + your engineer's spec - Delivered same day, before you leave the site - Free 15-minute call to walk your builder or engineer through the report

When to book: the day BEFORE the pour is scheduled. Not the day of. That gives you a full 24 hours to have any issues corrected before the trucks arrive.

Price: $550 for standard homes up to 220m². Larger homes quoted individually.

Book a Pre-Pour Slab Inspection: Call 07 3180 8041 or book online.

Where This Inspection Sits in Your Build

Independent stage inspections work best as a sequence — each one checks work that the next stage covers up for good. Here's the full pathway for a typical Queensland new-home build, and where the pre-pour slab inspection fits:

1. Pre-Pour Slab Inspection — you're reading this now 2. Post-Pour Slab Inspection — after the slab is poured and stripped 3. Frame Inspection — Timber Frame or Steel Frame, depending on how your home is built 4. Pre-Plaster (Lockup) Inspection — before the plasterboard hides the services 5. Practical Completion (PCI) Inspection — before you release your final payment

Next: Post-Pour Slab Inspection →

Pre-pour is the first — and most time-critical — inspection of the build. Booking the whole sequence with one independent inspector means every stage is checked against the last. Book your inspection or call 07 3180 8041.

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This guide is general information based on Australian Standards and Queensland residential construction practice. Specific site conditions, wind classifications, and soil types will change some requirements — your engineer's site-specific drawings are the primary reference for your build. This guide is not a substitute for a licensed inspection.