40mm subbase guide

Sub-grade is the earth surface that the project will be laid on. The topsoil should be removed to expose a stable surface. Try to remove any organic matter that may be growing.

The thickness of the topsoil can vary but it tends to be 100mm to 275mm thick. The exposed surface should be reasonably level and flat. Terram geotextile should be laid over the subgrade to prevent the sub-base sinking into the sub-grade.

The subbase layer should be laid on top of this. Sub-base is made up of a mixture of aggregates of various sizes which should compact down. We recommend using an aggregate based sub-base, as using hardcore ect. will not compact down as well and may cause future problems. The subbase should be laid to a minimum of 75mm on a area which will be having foot traffic, 100mm - 125mm thick for domestic driveways. The subbase will need to compact using a vibrating drum or a "waker plate". The finished surface for the sub-base should not deviate by more then +/- 10mm.

It is very important to consider your bedding layer. The bedding layer will help to support your paving slabs. The specification of a bedding layer can very, normally dependant on the weight it is expecting to take.                                                                                                                   

You may also want to check out pavingexpert.com, run by resident expert Tony McCormack, which contains lots of helpful articles on how to select and install subbase.