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Concrete - how to use it

When planning to use concrete around the garden, its intended use will affect a number of factors in how you do it. The uses covered below are:

The main factors to consider are:

  • The concrete mix - all the uses here need 1:3½ cement:all-in ballast or 1:1½:2½ cement:sharp sand:gravel.
  • The thickness of the concrete - the figures quoted below are the minimum.
  • The thickness of the sub-base - compacted rubble etc onto the subsoil before the concrete is poured.
  • The slope of the concrete - without a slope, water will tend to gather in depressions, the figures quoted are the minimum, with footpaths and drives any sloping of the land may be more than enough. Where the concrete goes up to a wall, always run the slope away from the wall. Any concrete against a building must slope away from it.
  • The need for any expansion joints - the quoted distances is the maximum, it will often be better to even out the spacings. As a 'rule of thumb', the distance between joints should be about 30 times the thickness of the concrete.

Concrete footpaths

A simple concrete pathway up to about 1m wide used solely for foot traffic:

  • The thickness of the concrete - 75mm (3 inches).
  • The thickness of the sub-base - none normally required.
  • The slope of the concrete - minimal - the trouble with planning no slope is that the middle of the pathway may settle causing areas where rain will collect.
  • The need for any expansion joints - every 2 metres (6ft 6in).

Extended slabs

A patio or similar area taking just foot traffic, chairs and tables:

  • The thickness of the concrete - 100mm (4 inches).
  • The thickness of the sub-base - 100mm (4 inches).
  • The slope of the concrete - 1 in 60 (16mm in 1 metre, 5/8in in 3 ft).
  • The need for any expansion joints - every 3 metres (10ft).

Driveways and Parking areas

  • The thickness of the concrete - 125mm (5 inches) for family sized car or 150mm (6 inches) for light vans etc.
  • The thickness of the sub-base - 150mm (6 inches).
  • The slope of the concrete - 1 in 40 (25mm in 1 metre, 1in in 3 ft) for driveways, 1 in 60 (16mm in 1 metre, 5/8in in 3 ft) for parking area.
  • The need for any expansion joints - every 4 metres (13 ft).

A pad for light structures

  • The thickness of the concrete - 75mm (3 inches).
  • The thickness of the sub-base - 75mm (3 inches).
  • The slope of the concrete - 1 in 80 (12.5mm in 1 metre, ½in in 3 ft).
  • The need for any expansion joints - every 3 metres (10ft).