How to Prepare for a Concrete Pour: Step-by-Step

This guide walks through each stage in order. Some steps are realistic DIY work. Others, particularly formwork for structural slabs or anything requiring an engineering spec, should be left to a licensed concreter. Read through the whole process first so you understand how each step feeds into the next.

Measure the area accurately and draw a simple plan to scale. Note the finished surface level relative to existing paving, drainage, and structures. You need to know the slab thickness before you can calculate excavation depth, concrete volume, or reinforcement requirements.

Check council and utility requirements

In most Australian states, a concrete driveway that involves a new or altered kerb crossover needs council approval. Brisbane, Sydney, Melbourne, Perth, Adelaide, and most regional councils each have their own crossover specifications. Contact your local council before you do anything near the kerb. Dig safely, too: call Dial Before You Dig (1100 or dialbeforeyoudig.com.au) at least two business days before any excavation. This is not optional.

Decide on slab thickness and mix

A standard residential path or patio is typically 85-100 mm thick. A driveway for passenger vehicles needs at least 100 mm, often 125 mm with mesh reinforcement. Anything carrying heavy vehicles, or any structural slab like a garage floor tied to footings, should be designed by an engineer. The mix specification (usually expressed as N20, N25, or N32 in Australia) also matters. Your concreter or the concrete plant can advise on the right grade for your application.

Mark out the area with pegs and string lines set to finished surface level. Your excavation depth equals the slab thickness plus the compacted sub-base depth, typically 75-100 mm of compacted road base or gravel. So a 100 mm slab on 75 mm of compacted base means digging down 175 mm from finished level.

Excavation tips

• Remove all topsoil and organic material. Concrete over organic matter will settle and crack.
• In clay-heavy soils (common across Melbourne, parts of Sydney, Perth, and Brisbane), over-excavate an extra 50 mm and replace with compacted rubble or road base.
• Keep the base as even as possible. High spots will reduce your slab thickness; low spots waste concrete.
• If the area is larger than a small path, hiring a mini excavator is worthwhile. Manual digging for a 40 m² driveway is exhausting and slow.

Compact the sub-base thoroughly

Hire a plate compactor and make at least two passes over the sub-base in perpendicular directions. The base should not shift underfoot. A poorly compacted base is the single most common cause of cracked residential slabs in Australia.

Formwork is the temporary frame that holds wet concrete in shape until it sets. For most residential work, 45 mm x 90 mm timber planks on edge work well. Steel form stakes, driven into the ground every 600-900 mm, support the planks and hold the level.

Setting levels accurately

Use a builder's level or laser level to set the top edge of your formwork to finished concrete height. The top of the form plank is your screed guide. Get this wrong and your slab will be uneven. Check your falls, too. Concrete paving near structures should fall away at a minimum of 1:100 (10 mm per metre) to direct water away from buildings. Australian Standards and most council specifications require adequate drainage from the outset.

What to check before leaving the formwork

• All corners are square (use the 3-4-5 triangle method).
• Stakes are driven firmly and form planks cannot flex under hand pressure.
• Internal dimensions match your plan.
• All penetrations, pipes, or conduits are positioned and secured so they stay put during the pour.
• Apply a thin coat of form oil or old diesel to timber surfaces so the formwork releases cleanly after the pour.

Most residential slabs use SL72 or SL82 steel mesh (standard mesh sizes readily available from Bunnings, steel merchants, and concrete suppliers across Australia). Cut sheets to size with bolt cutters, overlap joins by one full square, and tie with wire.

Keeping mesh at the right height

Reinforcement needs concrete cover above and below it to protect against corrosion. For a 100 mm slab, mesh typically sits at mid-depth or slightly above centre, around 40-50 mm from the bottom. Use plastic bar chairs ("chairs" or "biscuits") at 800 mm intervals to hold the mesh at the correct height. Mesh sitting on the ground provides no structural benefit. This is a very common DIY error.

For structural slabs, footings, or anything with an engineering specification, follow the engineer's drawings exactly. Do not substitute bar sizes or change spacing without written approval.

Once formwork and reinforcement are in place and inspected, order your concrete. In Australia, ready-mix concrete is supplied by companies including Boral, Holcim, Hanson, and numerous independent batching plants. Most require 24-48 hours notice for residential deliveries, sometimes more in rural areas.

What to tell the plant

• Concrete grade (N20, N25, N32, etc.)
• Slump (workability), typically 80-100 mm for standard work, higher if pumping
• Volume in cubic metres (length x width x thickness, plus your 5-10% buffer)
• Delivery time and site address, including any access limitations (low-hanging trees, narrow laneways, soft verges)
• Whether you need a pump truck (necessary if the truck cannot get within around 3-4 metres of the pour area)

Line up your labour

A concrete pour is not a solo job. A standard 4 m² path might be manageable alone, but anything larger needs at least two people: one guiding the chute and screeding, another working the concrete back and checking levels. For a full driveway, three or four people is more realistic. If you are hiring a concreter, confirm crew numbers with them in advance.

General market rates for a standard broom-finish concrete slab in Australia are roughly $65-90 per m² supplied and laid. Decorative finishes like exposed aggregate or coloured concrete typically run $100-150 per m². These are broad ranges only. Real costs vary significantly based on excavation, access, local labour rates, and site conditions. Always get a written quote before committing.