What Is Chip Sealing? How Is It Done?

What Is Chip Sealing?

Chip sealing is a surface treatment in which a bituminous binder is sprayed onto the road and immediately covered with a layer of single-sized aggregate chips. The chips are rolled into the binder, creating a waterproof, textured and skid-resistant wearing course. It is also known as surface dressing, seal coat or bituminous surface treatment.

Chip sealing is used for two purposes. On new roads, it is applied as the final surface over a prepared granular base. On existing roads, it is a maintenance treatment that renews an aged, cracked or polished surface, keeps water out and extends the life of the pavement.

Road authorities and municipalities around the world use chip sealing widely on rural, inter-city and low- to medium-traffic roads.

Single and Double Chip Seal

A single chip seal consists of one layer of binder and one layer of chips. It is the most common maintenance application for renewing an existing surface and restoring waterproofing.

A double chip seal repeats the process twice. The first layer is laid with larger chips and the second with smaller chips. The smaller chips fill the gaps between the larger ones, creating a denser and more durable surface. Double chip seals are preferred for the initial surfacing of new roads and on sections with heavier traffic.

Chip sizes, binder type and application rates are set by the project specification.

How Is Chip Sealing Done?

1. Surface preparation

On existing roads, potholes are repaired, cracks are sealed and damaged sections are corrected. The surface is cleaned of dust and loose material, as dirt prevents the binder from bonding. On new roads, a prime coat is first applied to the compacted granular base. The prime penetrates the top of the base, binds the dust and helps the surfacing bond to the base.

2. Spraying the binder

An asphalt distributor sprays the binder onto the road at a set rate and with even coverage. Depending on the specification, hot bitumen or bitumen emulsion is used. This step directly determines the quality of the chip seal. Too little binder and the chips do not hold and are lost under traffic. Too much and the binder bleeds to the surface, making the road slippery and soft in hot weather. This is why proportional asphalt distributors, which keep the rate per square metre constant regardless of vehicle speed, are preferred.

3. Spreading the chips

The chips are spread immediately after the binder is sprayed. They must reach the surface before hot bitumen cools or before emulsion breaks. The chip spreader distributes the chips in a single, uniform layer without gaps. The chips should be clean, dust-free and cubical; dusty or wet chips do not bond well to the binder.

4. Rolling

The chips are pressed into the binder by rolling. Pneumatic-tyred rollers are generally used for chip sealing, as the tyres embed the chips without crushing them. Vibratory rollers are avoided because they can break the chips. Rolling should start immediately after the chips are spread.

5. Sweeping and opening to traffic

Once the binder has set sufficiently, loose chips that have not bonded are removed with a road sweeper. Loose chips can damage vehicle windscreens and paintwork. The road is opened to traffic with a speed limit during the first days; slow-moving traffic helps the chips settle into place. Finally, road markings are applied.

Conditions for Chip Sealing

Chip sealing is sensitive to weather conditions and is therefore carried out during the warm, dry season.

• Air temperature: At low temperatures the binder cools quickly and the chips do not bond. The minimum temperature for application is given in the specification.
• Rain: Chip sealing is not carried out in rain or on wet surfaces. Rain shortly after application can also delay the breaking of emulsion and cause chip loss.
• Surface: The surface must be dry, clean and free of dust.
• Coordination of crew and equipment: The distributor, chip spreader and rollers must follow each other closely. The longer the gap between them, the poorer the chip retention.

Advantages and Limitations of Chip Sealing

Advantages: Chip sealing costs much less than hot mix asphalt and uses less material. It is quick to apply, and the road can be reopened to traffic in a short time. It waterproofs the surface and protects the underlying layers. Its textured surface provides good skid resistance, especially in wet weather. It is one of the most effective ways to keep an existing road in service for many years without straining the budget.

Limitations: Chip seals have a shorter service life than hot mix asphalt and need to be renewed at intervals. Because of their texture, they do not match hot mix asphalt in ride comfort and tyre noise. They are not suitable for heavy, high-traffic roads or junctions with frequent braking and turning. Chip sealing also does not add structural strength; it protects the surface but does not repair a failed base.

Chip Seal vs. Hot Mix Asphalt

The two methods are less alternatives than answers to different needs. Traffic volume, budget, the current condition of the road and the expected service life determine which one is chosen. For other surface treatments such as crack sealing and micro-surfacing, see our guide to road maintenance methods.

Chip Sealing Equipment

Asphalt distributor: Heats, transports and sprays the binder onto the road at a set rate. It is the machine with the greatest influence on chip seal quality. Vimpo VAD Series asphalt distributors are available with spray widths of 3,000 - 5,400 mm and fully automatic proportional control.

Chip spreader: Spreads the chips evenly over the binder in a single layer. The self-propelled chip spreader receives chips from trucks and distributes them at a constant rate across a wide spreading width. For smaller-scale work, a dump truck chip spreader mounted on the truck's tipper can be used.

Combi chip spreader: Combines binder spraying and chip spreading in a single vehicle. Because the time between binder and chips is minimised, chip retention improves, and the work requires fewer vehicles and operators. The Vimpo combi chip spreader is designed for exactly this job.

Roller: Embeds the chips into the binder. Pneumatic-tyred rollers are preferred for chip sealing.

Road sweeper: Cleans the surface before application and removes loose chips afterwards. See road sweeper.

Crack sealing equipment: On existing roads, sealing cracks before chip sealing extends the life of the treatment. See asphalt crack router and asphalt crack filling machine.

Bitumen storage and transport:Mobile bitumen tanks deliver the binder to site hot and without interruption. Authorities and contractors working with emulsion can produce their own with a bitumen emulsion plant.

Factors Affecting Chip Seal Cost

The cost of chip sealing per square metre cannot be expressed as a single figure; it varies from project to project and from year to year. The main cost factors are: single or double application, the type of binder and current bitumen prices, the distance from the quarry to the site, the extent of repairs needed before sealing, the size of the job and the equipment used. A correctly calibrated distributor directly reduces total cost by preventing binder waste.

Frequently Asked Questions

Is chip seal the same as asphalt?

No. Both use bitumen as the binder, but they are applied differently. In chip sealing, the binder is sprayed onto the road and covered with chips. In hot mix asphalt, bitumen and aggregate are mixed at a plant and laid on the road as a mixture.

Why do chips fly off a new chip seal road?

On a newly chip-sealed road, some chips that have not fully bonded remain on the surface for a while. These are removed by sweeping, but fast traffic in the first days can throw them up. That is why speed limits on newly sealed roads are important, both to protect vehicles and to let the seal settle. Continuous chip loss is usually caused by insufficient binder, dusty chips or application in cold weather.

How long does a chip seal last?

Service life depends on traffic load, climate, application quality and whether a single or double seal is applied. Chip seals have a shorter life than hot mix asphalt and are renewed at intervals to extend the service life of the road. A correctly dosed binder and clean chips are the most important factors in how long a chip seal lasts.

When is chip sealing carried out?

Because it requires warm, dry weather, chip sealing is carried out during the warm season. The exact application conditions are set out in the project specification.

Vimpo Chip Sealing Equipment

Since 1997, Vimpo has been manufacturing chip sealing equipment including asphalt distributors, self-propelled chip spreaders, combi chip spreaders and road sweepers. Contact our team to choose the right equipment for your project.