Chip Spreader: How Chip Seal Stone Is Spread and Rolled

A chip spreader is the machine that puts the "chip" in chip seal. Behind an asphalt distributor that sprays a hot film of binder, the spreader lays a single, even layer of small, clean stone. Rollers follow close behind to press that stone into the binder. Timing is everything: the chips have to land while the binder is still fluid enough to grab them. This guide covers the main types of spreaders, typical rates, how crews calibrate them and the mistakes that leave a road shedding stone.

Crushed stone calculator →

Quick facts

Job: spread cover aggregate evenly onto fresh chip seal binder.
Typical chip rate: about 15 to 50 lb per square yard, per FHWA.
Typical binder rate under it: about 0.35 to 0.50 gallons per square yard.
Target embedment after rolling: about 50 to 70 percent of chip height.
Main types: self-propelled, tailgate (truck-mounted) and small hopper or bucket spreaders.

Where the chip spreader fits in a chip seal train

The road is swept and patched.
An asphalt distributor truck sprays binder, often an emulsion such as CRS-2, across the lane.
The chip spreader follows close behind and drops the stone.
Pneumatic rubber tire rollers seat the chips.
After curing, sweepers remove the loose stone, and some agencies add a fog seal.

If the spreader falls too far behind, an emulsion can break and skin over before the stone lands, and the chips never bond properly.

Types of chip spreaders

Type	How it works	Typical use
Self-propelled	Dump trucks back up and feed a receiving hopper; conveyors move stone to a full-width spreading hopper with adjustable gates	Highways and county roads
Tailgate spreader	A spreading box with a feed roll mounted on the back of a dump truck that drives in reverse	Smaller agencies, short runs, private roads
Hopper or bucket spreader	A small box on a skid steer or a wheeled cart	Patches, driveways, narrow areas

Modern self-propelled machines often have computer-controlled gates that hold the rate steady as ground speed changes, and individual gates can be shut so the spread width matches the binder shot.

Calibrating the spread rate

Design starts with the chip size and shape. Then the spreader has to hit that rate in the field. A common check: lay a canvas or pan of known area on the road, run the spreader over it at working speed, then weigh the stone caught and divide by the area. Do this across the width, since gates can wear unevenly. Too little stone leaves bare binder that sticks to tires; too much leaves loose chips that roll and get thrown by traffic. A single layer, about one stone deep, is the goal.

Rolling right behind the spreader

FHWA describes chips being rolled immediately after spreading. Rubber tire rollers knead the stones down into the binder without crushing them, and they reach into small dips that a steel drum would bridge. Several passes are normal. The target is about half to two-thirds embedment; less and the stone pops out, more and the surface can bleed in hot weather. Keep traffic slow until the binder cures, often with a pilot car.

Common problems traced to the spreader

Streaks: a sticking gate or worn roll leaves thin lines with exposed binder.
Heavy loose stone: over-application; see loss of cover stone for the other causes.
Poor stick: dusty or wet chips. Many agencies require washed or precoated chips.
Long gap behind the distributor: binder sets before stone lands.

Estimating chip tons

A made-up example: one mile of road, 20 feet wide. That is 5,280 × 20 = 105,600 square feet, or about 11,733 square yards. At an assumed design rate of 25 lb per square yard, the job needs about 293,000 lb of chips, roughly 147 tons, plus some extra for waste and stockpile loss. A double chip seal needs two layers, usually of different sizes. For a private road or driveway, the crushed stone calculator and gravel calculator help with base stone, and the driveway asphalt calculator shows what paving the same area with hot mix would take. For what to expect once the work is done, read chip seal roads.

Questions people ask

What is a chip spreader?

It is the machine on a chip seal job that spreads the cover stone. A distributor truck sprays hot binder or emulsion on the road, and the chip spreader follows right behind, dropping an even layer of small aggregate onto the wet binder before it sets.

What types of chip spreaders are there?

Self-propelled spreaders that back into dump trucks and carry the stone forward on conveyors, tailgate spreaders that hang off the back of a dump truck, and small hopper or bucket spreaders for skid steers and patch work.

How much stone does a chip spreader put down?

It depends on the chip size and design. FHWA's pavement preservation guide gives typical chip rates of about 15 to 50 pounds per square yard, over binder at roughly 0.35 to 0.50 gallons per square yard.

How is a chip spreader calibrated?

Crews set the gates for the design rate, then check it by laying a tarp or pan of known area, running the spreader over it and weighing the stone caught. They adjust until the measured rate matches the design.

How soon after the spreader do rollers run?

Right away. FHWA describes chips being rolled immediately to press them into the binder, aiming for about 50 to 70 percent embedment. Pneumatic tire rollers are the usual choice because they press chips in without crushing them.

Why are there loose chips after a chip seal?

Some extra stone is normal, and it is swept up after the binder cures. Lots of loose stone can mean the spreader put down too much, the binder rate was low, or the chips were dusty or wet and did not stick.

As an Amazon Associate, AsphaltTons.com earns from qualifying purchases. Product links below are sponsored.