Surface dressing binders are specified under the framework specification BS EN 13808. For the design of the dressing itself, TRL Road Note 39 is the guidance to use, and the finished work is referenced against BS EN 12271.
Road Emulsion Association, Technical Data Sheet No.4
What surface dressing is for
Surface dressing with bitumen emulsion is a well established road surface treatment. It is designed as a repair and maintenance process, and it is critical that the system is used at the appropriate stage in a road’s life rather than as a substitute for reconstruction.
Performance has moved on considerably. Recent years have seen a marked increase in the technical performance of emulsion binders and in on-site application techniques, which has in turn improved the performance and durability of the finished dressing. That is mostly down to two things: wider use of polymer modified emulsion binders, and the use of encapsulation treatments.
The systems available
There is no single surface dressing. Several processes exist and choosing the right one for the road matters.
Single binder application
- Single surface dressing. A layer of binder followed by a layer of single sized aggregate chippings.
- Racked-in. A layer of binder followed by a double layer of chippings: larger single sized chippings first, then smaller single sized chippings.
Double binder application
- Double surface dressing. A layer of binder, then larger single sized chippings, then a second layer of binder and a final application of smaller single sized chippings.
- Inverted double surface dressing, the pad coat technique. A layer of binder, then small single sized chippings, then another layer of binder and a final application of larger chippings.
Binders and aggregates
Surface dressing emulsions in the UK are designed around BS EN 13808 and TRL Road Note 39. For guidance on the most applicable design process, Road Note 39 should be used.
Aggregate quality is not a detail. The cleanliness, dust content and physical and chemical properties of the chippings are critical to the success of the process. Excess dust on the aggregate interferes with the bond between binder and chipping, which is the whole mechanism the treatment depends on.
Encapsulation
Encapsulation locks surface dressing chippings into the surface. The result is a safer drive, particularly for cyclists and motorcyclists, a better looking road surface, and a carriageway that can be trafficked quickly after application.
Application and marking
Surface dressing requirements should be referenced against BS EN 12271, with critical controls on even and accurate application.
Products covered by a harmonised European standard carry a legal marking requirement. Since the UK left the European Union, UKCA marking applies alongside the earlier CE regime.
Related
All REA technical datasheets — twelve datasheets covering emulsion types, handling, surface dressing, bond coating and more.
The REA collects national data on surface dressing use in the UK and publishes these datasheets through its Technical Committee.