What is the best base for cobbles?

Michael Holmes replies: Cobbles are usually laid in 50-75mm of bedding mix (concrete or mortar) with the stones pushed in roughly half their depth. For a busy area with cars coming and going, this is laid on top of a sub base of approximately 100-150mm of well compacted interlocking aggregate such as MOT Type 1 Roadstone – try Mainland Aggregates (01234 831108; mainlandaggregates.co.uk), which has particles ranging from 35-40mm down to fine dust and, when compacted, bonds very tightly together. There is no need to include a membrane to control unwanted weeds, as they will not find their way through from below. If you have traditional square or rectangular cropped stone setts (sometimes mistakenly called cobbles), these are laid on to a semi-dry bedding mix 75-100mm over compacted aggregate, and then jointed with a cement mortar.