A Guide to Thermoplastic Road Markings
What is Thermoplastic?
Thermoplastic is a long life road marking material that was first used in the
USA in 1958, followed quickly by its introduction into many countries throughout
Europe. It is a mixture of glass beads, binder, pigment and filler material.
Thermoplastic as its name suggests has to do with heat. Dry thermoplastic
compound is generally heated in a thermostatically controlled pre-heater/boiler
to a temperature of 180-200 oC and agitated continuously until a homogenised
liquid is achieved, before transferring to an application vehicle. Applied at
this temperature, the thermoplastic melts into the upper surface of the asphalt
forming a thermal bond. When applying onto a concrete surface, the use of a tack
coat primer is recommended.
What is the purpose of each ingredient in the mixture?
Glass Beads - often called intermix beads in conjunction with the pigment, give
the material the retroreflectivity necessary for the bright night-time
Binder - is a mixture of plasticiser, waxes, anti-settling agents and resins
that hold all the other ingredients together;
- Plasticiser affects the flexibility and melt viscosity
- A blend of modified waxes is utilised to give the desired viscosity and
- Anti-settling agents help to keep aggregates and glass beads in
Pigment - supplies the colour - white or yellow to the thermoplastic.
Titanium dioxide pigment is used for the white thermoplastic and heat stable
yellow to make the yellow thermoplastic.
Filler Material - can consist of various grades of calcite (calcium
carbonate) quartz (silica) or calcined flint. Finer white grades are extender
added to assist the dispersion of pigment in the mixture, thereby providing
colour uniformity throughout.
What are the proportions of the Ingredients?
What thermoplastic is made of and how it is applied are the keys to its
durability and long lasting retroreflectivity. When properly formulated and
correctly applied, thermoplastic should last in excess of five years under
normal traffic conditions. The now superseded BS 3262 was a "recipe"
specification i.e. the proportions of each ingredient in the thermoplastic was
specified. However IS EN 1871: Road Marking materials - Physical Properties
deals with a range of performance tests on the mixture i.e. the manufacturer
must decide what proportions will yield the best results from the seven
performance tests outlined in IS EN 1871.
Consists of a heated hopper mounted on a pram, which feeds hot molten
thermoplastic under gravity to a rectangular screed with a gate at the base. The
gate opening is set to produce the thickness specified for the hot thermoplastic
as it flows onto the pavement. Where immediate reflectivity is required, a
manually operated glass beads dispenser should be attached to the screed
applicator. For letters, numerals and hatched areas, a hand-held mould box is
filled manually using a bucket. Glass beads are then applied by hand. Generally
used for Stop Lines, Pedestrian Crossings, Letters, Arrows and Double Yellow
This process employs a mechanically propelled vehicle. Extrusion utilises an
auger or pump from a thermostatically controlled tank to extrude the hot
thermoplastic through a gate opening set to produce a line of pre-selected
thickness of material onto the road surface. Glass beads are automatically
applied to the molten line. Generally used on new road construction projects and
The principle of spray is - hot material, stored in a mechanically agitated
and thermostatically heated vessel, is sprayed under pressure through a nozzle
onto the road surface. The height and pressure of the nozzle control the width
of the line, while the pressure at the nozzle and the application speed controls
the thickness of the line. Specially constructed spray equipment can travel and
apply thermoplastic lines at a faster speed than extrusion. Sprayed applied
markings are ideally suited for overlaying partially worn extrusion lines. Spray
thermoplastic provides a low cost alternative to extrusion where an improvement
is required in terms of the performance characteristics of a line, without an
excessive increase in the thickness of the line.
Profiled markings are applied using a specially developed shoe that can form
the base line and ribs in one continuous process. The thixotropic nature of the
material enables the molten thermoplastic to form neat raised ribs. Profiled
Markings can be laid as a profiled edge line marking to enhance wet night
visibility and which, when overrun, will provide a sensory and auditory impulse
to the motorist. An important feature of Profiled Markings is an improved retro
reflectivity in wet conditions. Profiled markings thus offer safety benefits in
poor weather and additional sensory perception at all times.
A specified quantity of drop-on glass beads must be applied onto the molten
thermoplastic during installation for immediate retroreflectivity. For
Extrusion, Spray and Profiled Markings, glass beads are applied onto the molten
line from a pressurised storage tank. In order to achieve good reflectivity, the
glass beads should be embedded, and not submerged in the hot material.
A number of grades of thermoplastic are used depending on the application