Concrete work

Concrete is strong in compression and weak in tension, which is a technical way of saying it will carry a lorry and will crack if the ground under it moves. So the dig is the job. Topsoil and anything soft comes out until we are on firm ground, then a stone subbase goes in and is compacted in layers rather than dumped in one go. Skimp there and no amount of thickness above will save it. Thickness comes next and depends on the load. A patio or a path lives happily at around a hundred millimetres. A driveway with a car on it wants more, and a yard that takes a delivery lorry or a tractor wants more again, with steel mesh in it and a stronger mix. Fibres in the mix control the fine shrinkage cracking that happens in the first days. Mesh, correctly placed in the upper part of the slab rather than lying on the ground where it does nothing, is what holds the slab together once it does crack. Because it will crack somewhere, and that is the point of joints. We saw or form control joints in panels so the slab cracks along a straight line you cannot see instead of a jagged one across the middle. The last two are drainage and curing. Every surface gets a fall away from the house, never towards it, with a channel drain across a garage door or where the driveway meets the house. Where the ground is heavy or the site is tight, water has to go somewhere legal, so we plan a soakaway or a connection rather than sending it into the neighbour’s garden. Curing is the free part that people skip. Fresh concrete needs to be kept damp and covered for several days, and pouring in frost or in blazing sun without protection is how a surface ends up dusty and weak. We do not pour in a hard frost. We will say so and come back, which is cheaper than doing it twice.

Concrete, or paving?

Concrete is cheaper per square metre, faster to lay and has no weeds and no sunken blocks in five years. Paving is easier to lift and put back when a service has to be dug up, and it drains between the joints, which can matter where surface water has nowhere to go. Finishes make up a lot of the difference. Brushed, power floated, exposed aggregate and imprinted all start as the same pour, and the last two cost more because of the work done in the hours after it lands.