Asphalt: A mix of graded stone, sand and filler bound with bitumen. In the UK 'tarmac' is the everyday word for it.
Asphalt concrete (AC): The family of continuously graded asphalt mixes in BS EN 13108-1, including what used to be called dense bitumen macadam.
AC 6 dense surface: A fine surface course mix with a 6 mm maximum stone, commonly laid 20–30 mm thick on drives and paths.
AC 10 close surface: A slightly coarser surface course with a 10 mm maximum stone, commonly laid 30–40 mm thick.
AC 20 dense binder: A coarser binder course mix with a 20 mm maximum stone, commonly laid 50–60 mm thick under the surface course.
Binder course: The asphalt layer between the sub-base and the surface course. It carries and spreads the load.
Bitumen: The black, sticky binder refined from crude oil that holds asphalt together. Not the same as coal tar.
Bond coat: Another name for tack coat: a sprayed bitumen emulsion that glues asphalt layers together.
BS 594987: The British Standard for transporting, laying and compacting asphalt. The 2024 edition is current.
BS EN 13108: The European standard series for asphalt mixes, used in the UK with the guidance document PD 6691.
Camber: A raised centre line so water runs to both sides, used on roads and long drives.
Channel drain: A linear drain set into the surface, often across a garage entrance or the bottom of a slope.
Close-graded: A mix with little air space between the stones, making it denser and less permeable.
Compaction: Rolling or vibrating each layer to remove air and make it dense and strong.
Crazing: A web of fine cracks across a surface, usually a sign of an ageing surface or a weak base.
Cross-fall: A slope across the width of a surface so water runs off to one side.
Dense bitumen macadam (DBM): The traditional UK name for dense asphalt concrete binder and base mixes.
Dropped kerb: A lowered section of kerb and strengthened footway that lets vehicles cross the pavement legally.
Edge restraint: Kerbs, blocks or setts bedded and haunched in concrete that stop tarmac spreading at the sides.
Falls: The slopes built into a surface to move water to a drain, channel or border, often 1 in 60 to 1 in 80.
Formation: The prepared ground at the bottom of the excavation, on which the sub-base is laid.
Fretting: Loss of stones from the surface as the binder ages, leaving a rough, ravelled finish.
Geotextile: A fabric membrane laid on the formation to stop soil mixing into the sub-base.
Gully: A pot with a grating that collects surface water and connects to a drain.
Haunch: The concrete wedge behind a kerb or edging block that holds it in place.
Hot rolled asphalt (HRA): A gap-graded mix with a mortar of sand, filler and bitumen, often with chippings rolled in. Common on main roads.
Inlay: Replacing a planed-off layer with new asphalt at the same level.
MOT Type 1: A graded crushed-stone sub-base material that compacts to a dense, strong layer.
Overlay: A new asphalt layer laid over an existing sound surface after repairs and a tack coat.
Planing: Milling off a layer of asphalt with a planer, before an inlay or to keep levels at kerbs and doors.
Porous asphalt: An open-graded asphalt with connected voids so water passes through to a permeable base.
Pothole: A hole where the surface and sometimes the base have broken away, usually after water and frost get in.
Rutting: Grooves along wheel tracks where the surface or base has deformed.
Setts: Small natural stone blocks, often granite, used for borders and edging.
SMA (stone mastic asphalt): A gap-graded, binder-rich surface mix designed for durability and rut resistance on busier surfaces.
Soakaway: An underground chamber or crate unit where surface water is stored and soaks into the ground.
Sub-base: The compacted stone layer beneath the asphalt that carries the load.
SuDS: Sustainable drainage systems: managing rainwater close to where it falls, for example with permeable surfaces and soakaways.
Surface course: The top asphalt layer that you drive on. Also called the wearing course.
Surface dressing: Bitumen sprayed onto a surface and covered with rolled chippings. Known as tar and chip on driveways.
Tack coat: A thin sprayed coat of bitumen emulsion that bonds a new asphalt layer to the one beneath.
Type 3 sub-base: An open-graded stone sub-base with voids that store water, used under permeable surfaces.

Tarmac and asphalt glossary

Get a written tarmac quote