DIY Concreting — Full guide · Backyard projects
Detailed planning notes for pouring concrete at home. This guide covers when you may legally and safely pour, which mix to use for each job type, minimum slab thickness, and realistic strength development timelines for bag mixes.
Do not pour when ambient temperature is below 5 °C or above 30 °C, when rain is forecast within 48 hours, or when the subgrade is frozen or waterlogged. Hot weather accelerates set before you can finish; cold weather slows hydration below usable strength.
After placing, keep the slab under breathable curing blankets or damp hessian for at least seven days. Uncovered open-air curing is insufficient in wind or direct sun and leads to surface crazing.
Garden paths at 75 mm depth use a 1:2:3 cement:sand:aggregate ratio by volume. Driveway crossovers at 100–125 mm require a richer 1:1.5:2.5 mix and 20 MPa minimum compressive strength at 28 days. Shed bases at 100 mm sit between those ratios.
Never use the same bag count per square metre for a footpath and a vehicle crossover — the thicker, loaded slab needs more cement per cubic metre, not just more depth of the same weak mix.
Bag mixes develop strength slowly. Foot traffic is safe after 48 hours; light wheelbarrows after seven days; vehicle loading on driveways only after 28 days when the design strength (typically 20–25 MPa) is reached. Drilling anchor bolts before seven days risks blow-out along the still-plastic paste.
Strength at 24 hours is roughly 40–50 % of the 28-day value for general-purpose mixes — not full structural capacity.
Residential vehicle crossovers need at least 100 mm compacted thickness over a 75 mm crushed-rock sub-base, with mesh or fibre reinforcement. Garden paths may be 75 mm unreinforced over 50 mm road base.