Gravel & aggregates

1. 1

   Choose the stone

   Pick 20 mm angular gravel for driveways and 10 to 20 mm for paths and borders, avoiding rounded pea shingle anywhere with a slope.

2. 2

   Excavate

   Dig 50 to 75 mm for a path and 200 mm for a driveway, allowing for the sub-base as well as the loose stone.

3. 3

   Fit the edge restraint

   Install timber, steel or concrete edging first, so the gravel has something to hold it in place.

4. 4

   Lay membrane and sub-base

   Roll woven weed membrane over the subgrade with 150 mm laps, then compact MOT Type 1 in layers on driveways.

5. 5

   Lay a stabilisation grid where needed

   On drives and slopes, clip the grid panels together over the compacted base so the gravel cannot rut or migrate.

6. 6

   Spread and rake the gravel

   Spread to 40 to 50 mm loose, or 30 mm over a grid, then rake level and walk it in.

• Loose gravel in a front garden is permeable and counts as SuDS-friendly under GPDO Class F. ^[1]
• MOT Type 1 is specified to the Specification for Highway Works, Series 800. Use it for sub-bases under paving and driveways. ^[3]

• Loose gravel decorative depth: 40–50 mm over a permeable membrane. Less and the membrane shows through; more and it walks.
• Bulk density rules of thumb: gravel ~1.5 t/m³, MOT Type 1 ~2.0 t/m³ compacted, sharp sand ~1.6 t/m³.
• Always add a 5–10 % over-order on bulk aggregates, voids, spillage and the bottom of the bag are real.
• Bulk bags are nominally 1 tonne but actual mass varies ±10 %; weighbridge tickets are the only honest source.

Most gravel problems are the wrong stone rather than the wrong depth. Size, shape and use decide which one works.

• 10 mm shingle: comfortable underfoot, good for paths and borders, but small enough to be carried indoors on shoes and into the lawn by a mower.
• 20 mm shingle: the default for driveways and larger areas. Big enough to stay put, small enough to walk on and rake level.
• Angular gravels such as granite and limestone chippings lock together and stay where they are put. Rounded pea shingle rolls underfoot and migrates on any slope.
• Slate chippings look sharp in modern schemes and suppress weeds well, but they break down under vehicle traffic, so keep them off driveways.
• Cobbles and larger stone, 40 to 75 mm, work as decorative mulch and dry stream beds, not as surfaces you walk on.
• Self-binding gravel such as Breedon type gives a firm, path-like surface for garden paths and is much easier to push a wheelbarrow or pram over than loose stone.
• For a driveway, a gravel stabilisation grid is the difference between a drive that stays level and one you rake every month. It also lets you drop the loose layer to 30 mm.
• MOT Type 1 is a sub-base, not a finish. It is a graded crushed stone with fines that compacts to a solid layer at roughly 2.0 tonnes per m3 compacted.

• Laying gravel too deep. Above about 50 mm it behaves like dry sand and is unpleasant to walk on and impossible to push a barrow through. 40 to 50 mm decorative, 30 mm over a grid.
• Membrane straight onto loose soil with no sub-base under a driveway. The membrane holds the stone out of the mud for one winter and then ruts.
• No edge restraint. Without a timber, steel or concrete edge, gravel spreads into borders and lawn within a season.
• Ordering by volume then paying by weight. Suppliers sell bulk aggregate in tonnes; convert with the bulk density before you order, or you get a third less than you planned.
• Assuming a bulk bag is exactly a tonne. It varies by around 10 percent, and damp stone weighs more per m3 than the price list assumes.
• Using rounded pea shingle on a sloping drive. It migrates downhill continuously, no matter how often it is raked back.

• Volume to tonnes: multiply area in m2 by depth in metres, then by the bulk density. Gravel is about 1.5 t per m3, MOT Type 1 about 2.0 t per m3 compacted, sharp sand about 1.6 t per m3.
• Worked example: a 20 m2 path at 50 mm is 1 m3, so about 1.5 tonnes of gravel, which is one and a half bulk bags.
• Decorative gravels: roughly £60 to £130 per bulk bag delivered, with slate and specialist colours at the top of the range.
• MOT Type 1: roughly £40 to £70 per tonne delivered loose, cheaper by the full load than in bags.
• Weed membrane: about £1 to £2 per m2 for a proper woven geotextile. Do not use damp-proof membrane; it holds water on the surface.
• Always add 5 to 10 percent to any bulk order for compaction, spillage and the low corners you will find as you level.