Excavation and sub-base
Excavate to the correct depth, allowing for the sub-base, the slab thickness and any finish. Remove all topsoil, organic material and soft spots. Fill with MOT Type 1 and compact in layers — not in one deep layer.
Set the final levels with pegs and string lines before the sub-base goes down. Once the concrete is in, it's too late to fix the ground shape.
Formwork and levels
Fix formwork firmly to the correct level — it defines the top of the slab. If the formwork moves under the weight of the concrete, the level changes. Use timber or steel formwork, pegged and braced.
Set the fall for drainage at this stage. A 1:60 fall is typical for outdoor slabs so water runs off.
Reinforcement
If using mesh, place it on plastic or steel chairs so it sits in the middle of the slab. Mesh on the sub-base does nothing — it needs to be within the concrete to work. Overlap mesh sheets by at least 300mm.
For fibres, they're added during batching. With volumetric concrete, the fibres go in on site.
Weather and timing
Don't pour into standing water or onto frost. In hot or windy weather, the surface will dry too fast — have plastic sheeting ready to cover the slab after finishing. In cold weather, the concrete will cure more slowly.
Have enough people on site to place, level and finish the concrete in one go. Concrete starts setting as soon as it's mixed, and you can't stop mid-pour.
Related services
Need concrete for your project? We supply volumetric concrete across South Wales, mixed fresh on site to the exact quantity you need. Request a quote or call 01495 820164.