High friction surfacing relies on a precise combination of materials working together to improve skid resistance and keep road users safe. Understanding these materials (calcined bauxite aggregate, resin binders, and how they interact) is essential for anyone specifying or procuring HFS for highways, junctions, or commercial sites.
We break down each of the core materials used in high friction surfacing, compare the different resin binder types available, and explain how hot and cold applied systems differ in practice. Whether you're a highways engineer, facilities manager, or local authority decision-maker, this is what you need to know about the materials that make HFS work.
What Is High Friction Surfacing and How Does It Work?
High friction surfacing is a specialist road treatment that increases the skid resistance of a surface. Rather than leaving a smooth, polished finish, HFS creates thousands of tiny contact points across the treated area – known as a micro-texture. These contact points give vehicle tyres more contact with the road, allowing them to better grip the surface and come to a safer stop.
The way this is achieved is through combining a resin binder with a hard-wearing aggregate, typically calcined bauxite. The binder adheres to the road surface and locks the aggregate in place, producing a durable, high-friction finish that withstands heavy traffic and adverse weather conditions.
Since its first UK trials in 1967, HFS has delivered proven results. Those early installations showed an immediate 50% reduction in skid-related accidents and casualties. More recent data from the MOLASSES monitoring programme, which monitored a total of 2,309 road safety schemes between 1991 and 2001, recorded an accident reduction rate of 35.1% based on a site balance of 10% rural and 90% urban roads.
Why Is Calcined Bauxite the Preferred Aggregate?
Calcined bauxite is the only aggregate type with a proven long-term track record in high friction surfacing. It's a manufactured material, produced by heating raw bauxite clay in a kiln at extremely high temperatures. This calcination process transforms the clay into an exceptionally hard aggregate with outstanding anti-skid properties.
What Makes Calcined Bauxite So Effective?
Two properties set calcined bauxite apart from other aggregates. First, its resistance to abrasion – vehicle tyres grinding over the surface day after day don't wear the aggregate down quickly. Second, and equally important, is its resistance to polishing. Many aggregates lose their grip over time as traffic smooths their surface.
Calcined bauxite retains its rough micro-texture far longer, which means the anti-skid properties have the longest possible lifespan. A SCRIM survey conducted on London roads in 2015 concluded that on sites requiring an Investigatory Level of 0.55 or above, calcined bauxite outperformed other aggregate types over time.
Technical Specifications for Calcined Bauxite
For Type 1 high friction surfacing applications calcined bauxite must meet demanding specifications. These include a Polished Stone Value (PSV) of 70 or above, an Aggregate Abrasion Value (AAV) of 4 or less, a particle density of at least 2.8, and moisture content no greater than 0.5%.
This level of specification exists for good reason. The aggregate is the component that makes direct contact with vehicle tyres, and any compromise in quality directly affects skid resistance and service life.
What Types of Resin Binder Are Used in HFS?
The binder is the material that bonds the calcined bauxite aggregate to the road surface. Different binder types suit different applications, and they fall into two broad categories: cold applied resins and hot applied thermoplastics.
Cold Applied Resin Binders
Cold applied systems use a liquid resin adhesive that's blended mechanically and applied directly to the prepared road surface, typically using a serrated squeegee and/or roller at the prescribed coverage rate. Once the resin is spread, an excess of calcined bauxite aggregate is broadcast over the top. After the binder has sufficiently cured, excess aggregate is removed by vacuum sweeper or by hand sweeping, leaving a firmly bonded, high-friction finish.
The following types of cold applied resin have been assessed and approved for use in HFS:
- Epoxy resin
- Bitumen-extended epoxy resin
- Polyurethane (PU) and polyurea
- Methyl methacrylate (MMA)
- Polyurethane-modified MMA
Cold applied systems don't require heavy-duty heating equipment, which can make them a safer and more practical option in certain environments. They also offer a smoother finish compared to hot applied systems and reduced energy consumption during application, making them well suited to pedestrian areas, cycle lanes, and bus lanes.
Hot Applied Thermoplastic Binders
Hot applied systems take a fundamentally different approach. The resin and aggregate arrive on site pre-mixed in bags. This material is heated in a specialist pre-heater to a high temperature until it is mixed and workable, then discharged into buckets, transferred by hand to a screed box, and applied in adjoining strips across the road surface.
The two main hot applied binder types are:
- Rosin ester thermoplastic
- Hydrocarbon resin thermoplastic
Hot applied systems offer excellent bond strength to the road surface and are highly durable, making them suitable for high-traffic areas. They also cure faster than many cold applied alternatives, which means less disruption and quicker road reopening – an important consideration on busy routes.
The trade-off is that hot application requires specialist heating equipment and careful temperature monitoring throughout the process. Material temperatures must be periodically checked using calibrated probes accurate to ± 2°C to ensure the maximum and minimum application temperatures are maintained and the safe heating temperature is not exceeded, as overheated materials have the potential for premature failure.
How Do Hot and Cold Applied Systems Compare in Practice?
Both hot and cold applied systems can achieve Type 1 classification (the highest performance standard) when installed correctly with calcined bauxite aggregate. The choice between them depends on site conditions, traffic levels, and practical considerations.
A two-year study conducted by the BBA in 2013–14 concluded that the vast majority of HFS sites investigated gave a minimum service life of five years. On average, hot applied systems demonstrated eight years of life, while cold applied systems averaged twelve years. This difference is worth considering during specification, particularly when weighing up long-term maintenance costs.
Both system types must comply with Specification for Highway Works Clause 924, which requires HAPAS certification. Successful certification under the HAPAS scheme involves meeting demanding performance criteria and stringent quality assurance and quality control requirements on an ongoing basis. Only HAPAS-approved installers are permitted to carry out the work, and operatives should hold NVQ Level 2 qualifications along with CSCS cards.
Where Are These Materials Most Commonly Applied?
High friction surfacing is specified wherever vehicles need maximum tyre grip to brake safely or maintain control. The most common locations include approaches to major junctions, approaches to pedestrian crossings where pedestrians or other vulnerable road users may misjudge the speed of the traffic (for example near schools or where the approach speed is high), roundabout approaches, bends with a radius tighter than 500 metres on single carriageways where risk factors are present, and highway slip roads.
Beyond highways, HFS materials are also used in car parks, bus lanes, cycle lanes, and traffic calming schemes. Coloured surfacing options allow the material to serve a dual purpose – improving grip while visually reinforcing lane delineation or hazard warnings.
The economic case for HFS is well documented. According to The London Accident Analysis Unit, of the 1,700 roads treated with high friction surfacing in London alone, there were savings of £24 million from a total cost of £3 million. With one motorway fatality thought to result in costs of up to £1.4 million, the first-year return rate was calculated at 352%.
How Should You Choose the Right HFS Materials?
Selecting the right combination of binder and aggregate depends on several factors. Traffic volume and the proportion of commercial vehicles determine whether a Type 1, Type 2, or Type 3 system is required. Site geometry influences whether a hot or cold applied system is more appropriate. Surface condition matters too – HFS should only be applied to sound substrates free from cracks, rutting, or surface fatting.
Environmental conditions during installation also play a role. Both hot and cold systems have specified temperature ranges that must be met for a successful, durable application. Getting the specification wrong at any stage can compromise the entire installation, which is why working with experienced, HAPAS-approved contractors is essential.
Expert High Friction Surfacing from Northern Marking
Northern Marking delivers professional high friction surfacing across Manchester and Northern England. With over 20 years of specialist experience, Sector 7 scheme approval, and ISO 9001:2015 quality assurance, we're one of the region's most experienced independent contractors.
We offer both hot applied systems using Hitex Type 1 and cold applied solutions using EcoGrip Type 1, allowing us to match the right materials to your site's specific requirements. We're authorised to carry out Section 278 works on public highways and approved by local councils, so whether it's a junction approach on a trunk road or a private car park, the job gets done properly.
Every project starts with a site survey to assess surface condition, traffic levels, and the most suitable system. We then handle everything from traffic management through to final inspection, keeping the process straightforward from start to finish.
For advice on high friction surfacing materials or to discuss a project, contact our team today.
