Common Mistakes to Avoid When Laying Concrete

Most concrete failures trace back to a short list of avoidable mistakes: poor site preparation, ignoring the weather, badly mixed concrete, skipped reinforcement, an overworked surface, rushed curing, uneven shuttering — or simply rushing the whole job. Avoid these eight and your slab should stay flat and crack-free for decades. Here's each one, and what to do instead.

Concrete poured over grass, roots or debris is a slab on borrowed time — organic material left underneath rots away, and the concrete above it cracks and settles unevenly. Clear the ground completely, then install a proper sub-base layer before any concrete goes down. The slab can only ever be as good as what it sits on.

Concrete and extreme weather don't mix. In hot conditions the concrete cures too fast and cracks; in cold conditions the water in the mix can freeze during the cure, permanently reducing the slab's strength. Check the forecast before booking a pour, and if the weather turns, protect the work — curing blankets in the cold, sunshades in the heat.

Improperly mixed concrete causes problems from reduced strength to a patchy, uneven finish. If you're mixing yourself, follow the manufacturer's guidance on water-to-cement ratios exactly and mix to a uniform consistency — too much water is the classic error. For most projects, the safer answer is ready-mixed concrete: it arrives consistent, batch after batch.

Concrete is strong under compression but weak under tension — an unreinforced slab under load will find its own way to crack. Use fibre reinforcement in the mix, particularly for structural slabs like garage bases and driveways. It's a small addition at the batching plant that strengthens the entire slab.

More trowelling is not better trowelling. Excessive working weakens the surface layer and can leave the slab prone to water pooling. Smooth the surface only until it's level, and once the bleed water has evaporated, stop — the concrete is telling you it's done.

Curing is where concrete gets its strength, and cutting it short can reduce the slab's durability by up to 50%. Keep the concrete damp for at least seven days for most mixes — a gentle hose-down helps, especially in hot conditions. A week of patience buys decades of durability.

The shuttering defines the slab, so it must be square, flat and level, with enough support to hold its shape before any concrete is poured. The classic DIY failures are shuttering that's out of level, undersized boards, or a frame that bulges or collapses under the weight of wet concrete — and every one of them is cast permanently into the base.

Every stage of a concrete job — preparation, shuttering, pouring, finishing, curing — needs its own share of care and time. Rush any of them and the finished slab pays for it. Our base teams' rule is simple: the job takes as long as the job takes.