Highways Agency

4. Application and Removal

4.1 Application and Removal Issues

This section deals with the issues relating to the application and removal of temporary road marking materials. Section 4.2 gives more information on the methods available for removing the markings and a summary of removal methods is given in Table 4.

4.1.1 Hot Applied Thermoplastic

Hot applied thermoplastic adheres to the surface and, once applied, the bond cannot be penetrated by moisture. However, this bond cannot be created in the presence of moisture and debris and, therefore, the surface must be dried and cleaned prior to application. Nevertheless, thermoplastic can be applied in low temperatures and to all surfaces. It can be applied in a wider range of weather and temperature conditions compared with self adhesive studs and temporary tape.

Thermoplastic can be applied more thinly than in the permanent situation and this can lead to benefits in terms of quicker removal and possible less damage to the road surface.

4.1.2 Temporary Tape

Temporary tape adheres to the road surface by a waterproof seal with the carriageway. If this seal is penetrated by water, the adhesion fails. For good adhesion, the road surface must be dry, clean, free from salt, and the ambient temperature needs to be above 4^oC. The surface is sprayed with a solvent-based primer which must then be left to dry. Tape is then applied onto the dry primer. Temporary tape does not perform well on open textured or rugous surfaces in wet conditions when water can flow through the surface and a pumping action causes the tape to lift.

At low temperatures, tape is less flexible and is less able to take the shape of the contours of the surface. The solvent based primers will not cure at low temperatures and cannot be applied in wet conditions.

There are situations when temporary tape can be removed easily and quickly from the road surface without leaving permanent residues, for example, when it is used as an edge line. However, if it has been constantly overrun for long periods, the polymer matrix can break up such that it can only be removed in small pieces. Under no circumstances should heat be employed to remove temporary tape as toxic fumes are given off.

4.1.3 Temporary Studs

Hot-melt temporary studs can be applied in all conditions, though this is dependent on the surface having been dried. Problems with adhesion can occur when steam pockets are created by the hot bitumen coming into contact with moisture that is resident in the voids of open textured surfaces.

Self adhesive temporary studs can be applied in most conditions, but the bitumen pad adheres less well at low temperatures. Drying of the surface prior to application is required. The stud adheres to the surface by the bitumen pad creating a waterproof seal with the surface. If this seal is penetrated by water the bond fails. Temporary self adhesive studs do not perform well on open textured or rugous surfaces. The application of a thixotropic glue prior to the installation of the self adhesive stud creates a waterproof seal between the bitumen pad and the surface and improves adhesion. This is particularly useful on thin surfaces.

Temporary studs can be removed from the road surface by sliding a shovel or "chipping bar" under the base of the stud. The most effective method of removal is by using a skid steer loader or tractor fitted with a bucket.

4.1.4 Road Marking Paint

Paint adheres to the surface by a chemical bond and its curing time is adversely affected by low ambient air temperatures, moisture and debris. The curing time prohibits its use during rain. Black paint requires a surface application of anti-skid material to aid abrasion and lessen highlight glare. White paint requires the application of glass beads to provide retroreflectivity.

Because paint is absorbed into the binder of the road, only the surface layer can be removed without damage to the surface. Masking with black paint is the only effective method. However, paint can be removed successfully from concrete carriageways because it is not absorbed.

4.2 Removal methods

Unless traffic is to be confined to a single lane delineated by closely spaced cones on each side (see Chapter 8, paragraph 3.1.3), where existing road markings conflict with temporary traffic management arrangements they must be removed or masked to avoid confusion in the interest of safety. Masking of the markings can be undertaken using temporary tape, thermoplastic or paint (see Section 2.3). The removal of road markings provides a permanent solution and avoids the possible failure of masking materials and consequent exposure of conflicting markings.

The main removal methods are as follows:

4.2.1 Hot Compressed Air (H.C.A.) Lance

This equipment works by using hot compressed air to vaporise the road marking. Because of the nature of the equipment used, it is regarded as a mechanical method of removal. The temperatures involved are likely to cause damage to the road surface and, for this reason, the equipment is inappropriate for use on thin surfaces. Noise, smoke and fumes are also important issues that need consideration. The H.C.A. lance operates at a relatively high noise level (120 dB(A)) and its appropriateness close to other site operations and urban areas must therefore be assessed. The vaporised thermoplastic can cause clouds of smoke which will affect drivers' visibility and, although not toxic, may be a health and safety issue.

4.2.2 Mechanical Scabbling

Mechanical scabbling grinds the marking from the surface, but total removal is not possible without damaging the surface. Small amounts of marking are left in the voids of the surface and this residue has to be masked or removed by other methods. The main use of mechanical scabbling is for removing the bulk of markings and the removal of raised ribline markings which are exceptionally thick. This method produces large amounts of debris that must be cleaned up quickly to avoid the thermoplastic particles re-adhering to the surface. The equipment is also relatively noisy and operates at 90 dB(A), but can peak to 104 dB(A).

4.2.3 Forced Air Abrasive (Shot Blasting)

Abrasive particles are projected by high pressure air at the road marking. The particles abrade the road marking from the road surface. This method leaves very little scarring because heat is not generated during the process but some polishing of the aggregate is likely. Total removal of road markings from porous/thin layer surfaces can only be undertaken with this process. The equipment is relatively noisy and operates at 105 dB(A). If this method is specified, the time factor must be considered because removal of road markings by shot blasting is very slow.

Consideration must be given to the environmental effects of the discarded abrasive material used during the removal process, especially in water courses. Captive shot blasting can be considered but the binder that is recycled with the abrasive material tends to clog the machinery.

4.2.4 Mechanical/hand chipping

This method is only suitable for removing temporary studs and tape.

4.2.5 New developments

New methods of removing markings are being developed. One that is commercially available is a method of forced air particle removal that employs dry ice as an abrasive particle. The dry ice vaporises during the removal process leaving very little debris. Another new system uses a heated mixture of sand and water applied at low pressure to remove markings. The developer claims that the removal process yields a relatively small amount of damp residue that can be swept up for later disposal.