Bitumen, usually in the form of an emulsion, is sprayed onto the road surface at an appropriate rate from the spray bar at the rear of a large tanker containing the bitumen emulsion, or cutback bitumen.
Chippings of an appropriate size are immediately applied to the bitumen by a large spreader which usually tows behind it a lorry containing the chippings.
The lorry being backed onto the spreader hopper.

The bitumen part of the surface dressing as well as securing the chippings to the existing surface will seal the old road surface, thus preventing the ingress of water.
Water if allowed to enter the road fabric, will cause severe damage to the strength/load carrying ability of the road and cause early road failure.

The chippings will restore texture to road surfaces that have become smooth with traffic wear.
The correct texture on a road surface is one of the most important aspects in preventing skidding accidents.
Only premium quality aggregate should be used in surface dressing, i.e. aggregate that is known will not become smooth under trafficking.

Surface dressing will NOT add any strength to the road pavement, BUT it does keep an already strong road in a strong condition for longer by sealing water out .