How to keep dust down on a gravel or dirt road

Why gravel roads dust

The gravel roads manual starts from a plain fact. "All gravel roads will give off dust under traffic."¹ That dust is the fine material that binds your gravel together, and every car or truck that goes by loosens a little more of it.

Losing those fines costs you more than dirty windows. The manual says the loss leads to washboarding and poorer skid resistance. It also points to studies that put the loss as high as one ton of gravel per mile each year for every vehicle that uses the road daily.¹ By that figure, a road carrying 200 vehicles a day loses 200 tons of gravel per mile each year.

How much fine material your gravel has matters too. The FHWA handbook uses the share passing a No. 200 sieve as its yardstick.²

What crews spray on dirt roads

Dust treatments fall into a few families. The USDA Forest Service lists water, water-absorbing products such as calcium and magnesium chloride, petroleum-based products, organic non-petroleum products such as lignin sulfonate, and synthetic polymers, among others.³ Each holds dust a different way. The full comparison, with what federal guides say about each, is in dust control products compared.

What we spray is lignin sulfonate, a plant-derived binder from wood pulping. A pass of water goes down first to pre-wet the road, then the truck sprays the lignin. You can drive on it right away, and on a hot summer day it's fully dry in about two hours. I drive the truck myself, out of Medford.

What you can do yourself

• Water, little and often. In the Forest Service's words, "Regular, light watering is more effective than less frequent, heavy watering."³
• Keep the crown and the ditches. The gravel roads manual says to give the driving surface a good crown and keep the shoulders draining, because standing water anywhere on the road softens the surface until it fails.¹
• Follow the label. If you buy a product, the Forest Service says to follow the manufacturer's minimum application rate, compaction and curing time, and to spread liquid products with a pressure distributor so they go down evenly.³
• Try a short stretch first. The manual suggests a test section of no more than 1000 feet to see how a product works with your gravel.¹
• Never waste oil. The manual says drain oil from engines harms the environment and breaks EPA rules.¹ Please leave it off your road.

Why treatments fail

The guides name the same handful of causes again and again.

1. Poor gravel. The manual says the money spent on a chloride treatment has been close to wasted on some roads where the gravel was poor.¹ The Forest Service calls for more product, more often, when fines are low or the surface is poorly bladed.³
2. No crown. Water that sits on the road softens it, and the treatment goes with it.
3. Rain on a fresh treatment. "If applied just before a rain, the material may wash away," the Forest Service warns.³ The manual puts it shorter and tells you to watch the weather.¹
4. A dry surface. The Forest Service advises dampening a dry surface before liquid treatments.³ That's why we always pre-wet with water before we spray.
5. Heavy, fast traffic. The Forest Service says higher rates or more frequent treatment are generally needed when a road carries a lot of fast traffic and a bigger share of trucks.³

When hiring a truck makes sense

I'd say hiring makes sense once the job is bigger than a hose. Think of a long drive or a shared road, heavy or truck traffic, several households who all want the same result, or a lot where customers park. The Forest Service recommends a pressure distributor so a liquid treatment goes down evenly, and that's what a spray truck is.³

We treat everything from a short driveway to miles of roadway and multi-acre lots, and we quote a shared road as one job. See gravel driveway dust control, or read what sets the cost before you call.

Southern Oregon specifics

The Rogue Valley dries out hard. NOAA's 1991–2020 normals for Medford give 0.68 inches of rain in June, 0.24 in July, 0.33 in August and 0.48 in September. June through August together bring 1.25 inches of a yearly 18.43, and the normal high in July is 91.6°F.⁴

Dry weather is when roads dust, and it's also when a treatment has the best chance of staying put. The timing guide covers when to book, or just give me a call.