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Concrete - different uses and mixes

The intended use of concrete around the garden will affect various factors, such as site preparation, sub-base, thickness of concrete and more. In this article we give guidelines for using concrete for various purposes, the purposes covered are:

The main factors to consider are:

  • The concrete mix - for all the uses below, use a 1:3½ cement:all-in ballast or a 1:1½:2½ cement:sharp sand:gravel mix (these are effectively the same, just using different materials). For calculating the amount of each material required for a job, refer to our Concrete Materials Calculator.
  • The thickness of the concrete - minimum figures are given below depending upon the use.
  • The need for, and thickness of, any sub-base - often just rubble etc compacted onto the subsoil before the concrete is laid.
  • The slope of the concrete - water will tend to gather in depressions on the surface of the concrete is no slope is introduced, the figures given below are the minimum necessary, when laying footpaths and drives the slope of the land may be more than enough but should always be checked. Where concrete is to be laid up against a wall, the slope must always run from the wall.
  • Expansion joints - any large area of concrete will tend to move, to avoid the concrete cracking, expansion joints may need to be introduced. The distances between any joints quoted below should be considered as the maximum, it often looks better is the required number of joints are equally spaced. As a rough guide, expansion joints should be no further apart than about 30 times the thickness of the concrete.

Concrete footpaths

A concrete pathway up to about 1m wide and only subjected to traffic:

  • Thickness of concrete - 75mm (3 inches).
  • Thickness of sub-base - none normally required.
  • Slope of the concrete - minimal and make it across the path - the problem with planning no slope, is that the concrete in the middle of the pathway will settle and will allow water to collect.
  • Expansion joints - every 2 metres (6ft 6in) along the length.

Large slabs

For a patio or similar area subjected to just foot traffic, chairs and tables:

  • Thickness of concrete - 100mm (4 inches).
  • Thickness of sub-base - 100mm (4 inches).
  • Slope of the concrete - 1 in 60 (16mm in 1 metre, 5/8in in 3 ft).
  • Expansion joints - every 3 metres (10ft) in both directions.

A pad for light structures

  • Thickness of the concrete - 75mm (3 inches).
  • Thickness of the sub-base - 75mm (3 inches).
  • Slope of the concrete - 1 in 80 (12.5mm in 1 metre, ½in in 3 ft).
  • Expansion joints - every 3 metres (10ft).

Driveways and Parking areas

Subjected to heavy traffic.

  • Thickness of concrete - 125mm (5 inches) for family sized car or 150mm (6 inches) for light vans etc.
  • Thickness of sub-base - 150mm (6 inches).
  • 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.
  • Expansion joints - every 4 metres (13 ft).