Road dust control products, compared without the sales pitch

No single best product

I'd be wary of anyone who says one product fixes every road. The FHWA's practitioner handbook on unpaved road dust is blunt about it, saying "contrary to some undocumented claims, there is no one chemical treatment that addresses all unpaved road problems."¹ Its way of choosing weighs the traffic (cars and trucks per day), the road's grades and curves, the climate, and the road material itself.

The products sort into a few families by how they hold the dust, and most of what matters to you as a landowner follows from that.

Side by side

Every line below comes from the FHWA handbook (2013), the FHWA/South Dakota LTAP gravel roads manual (2000) or the USDA Forest Service dust palliative guide (1999), put in plain words. None of it is my opinion.^1,2,3 The three ratings on each card come from the FHWA additive selection chart, for wet, damp-to-dry and dry climates.

• Water

  Not rated in the FHWA climate chart. Climate Not rated

  How it works

  Wets the surface. The Forest Service lists water as its own kind of dust suppressant.

  What the guides caution

  Light watering on a regular rhythm works better than heavy watering now and then. (USFS)

  Grading afterward

  Not covered by the guides.

• Calcium and magnesium chloride

  FHWA climate rating: Wet Poor, Damp–dry Good, Dry Poor. Wet Poor Damp–dry Good Dry Poor

  How it works

  Pull moisture from the air and keep the surface damp. They are not binders, so the gravel needs its own fines. (FHWA manual)

  What the guides caution

  Never apply to dry gravel. Rain on a fresh treatment can leach it out. Restrict use within 25 ft of low-salt-tolerant vegetation. (FHWA manual, USFS)

  Grading afterward

  Can be maintained with conventional unpaved road techniques. (FHWA)

  Ratings shown are for calcium chloride. The chart rates magnesium chloride fair in dry climates.

• Lignin sulfonate

  FHWA climate rating: Wet Poor, Damp–dry Good, Dry Good. Wet Poor Damp–dry Good Dry Good

  How it works

  Works like a glue that clumps the fines and the coarser particles together. (FHWA)

  What the guides caution

  Most are water soluble and can leach out in heavy rain. Check for drainage toward streams and ponds first. (FHWA, USFS)

  Grading afterward

  Can be maintained with conventional unpaved road techniques. (FHWA)

  The one product we apply

• Asphalt emulsions

  FHWA climate rating: Wet Fair, Damp–dry Good, Dry Good. Wet Fair Damp–dry Good Dry Good

  How it works

  A cementing action that adds strength and controls dust. They don't leach out in the rain. (FHWA)

  What the guides caution

  Cut-back asphalts have been banned in many places. (FHWA manual)

  Grading afterward

  Difficult to maintain with conventional equipment if a hard crust forms. (FHWA)

• Synthetic polymers

  FHWA climate rating: Wet Good, Damp–dry Good, Dry Good. Wet Good Damp–dry Good Dry Good

  How it works

  Glue the aggregate particles together as the water evaporates, and can add strength. (FHWA)

  What the guides caution

  Results depend on the formulation and application rate. (FHWA)

  Grading afterward

  Usually difficult to maintain with conventional techniques, because the surface crust gets damaged. (FHWA)

Water

Watering is the simplest thing to try, and it's the first category in the Forest Service's list of dust suppressants. Its advice on watering comes down to rhythm. "Regular, light watering is more effective than less frequent, heavy watering."³ The Forest Service also advises dampening a dry surface before you put down any liquid suppressant. That's why we pre-wet the road with water before the truck sprays.

Chlorides: calcium and magnesium

Calcium chloride and magnesium chloride are the most common products in the FHWA's water-absorbing family. The handbook says they have a long published record and a long history of use.¹ The gravel roads manual explains how they work. They pull moisture out of the air and keep the road surface damp all the time.²

The manual is just as plain about what they need.²

• Chlorides don't bind anything on their own, the manual says. The gravel itself needs a good share of fines to hold together.
• "Never apply the Chloride to dry gravel. It will not be evenly absorbed and may show failure in spots."
• Rain on a freshly treated surface can wash the chloride out, dilute it and run it off the road.
• It's best to keep traffic off the road for up to two hours after it goes down.

The Forest Service adds that dry air generally calls for higher rates, calcium chloride most of all, and it advises restricting chlorides where low-salt-tolerant plants grow within 25 feet of the treated area.³

Lignin sulfonate

This is the one we use, so I'll hold it to the same standard as the rest. Lignin sulfonate is a by-product of the pulp milling industry, "sometimes called 'tree sap' in the field."¹ The FHWA puts it with the organic non-petroleum products, which work like a glue that clumps the fines and the coarser gravel together. The same sources list its limits. Most are water soluble, and it can leach out in heavy rain.¹ The Forest Service advises checking whether drainage from the treated area could reach streams, ponds or lakes before you put it down.³ There's more in what lignin sulfonate is.

Asphalt emulsions, and why waste oil is off the table

The FHWA describes the organic petroleum treatments as mostly diluted asphalt emulsions. They add strength and hold dust by cementing the surface together, and rain doesn't wash them out. Upkeep is the hard part. Once a hard crust forms, the handbook says, they're difficult to maintain with the usual unpaved road equipment.¹ The gravel roads manual adds that cut-back asphalts have been banned in many places.²

I'll quote one caution from the manual in full, because people still ask me about it.²

"Do not use waste products such as crankcase drain oil from engines. This is harmful to the environment and is in violation of EPA rules."

Synthetic polymers and other binders

Synthetic polymer emulsions dry and leave behind ingredients that glue the gravel particles to each other. Depending on the formulation and the rate, the FHWA says they can work for both dust control and added strength. The trouble comes later, because roads treated with them are usually hard to maintain with ordinary unpaved road methods once the surface crust gets damaged.¹

The gravel roads manual also describes acidulated soybean oil soapstock. It's a by-product of refining soybean oil, biodegradable, and the manual says it behaves a lot like a light petroleum-based oil.²

Whatever you end up trying, I'd follow the manual's advice. If a treatment is new to your road, "try a test section" of no more than 1000 feet first, and see how it works with your gravel.²

What fits Southern Oregon's dry summers, and what we use

Climate is one of the FHWA's selection factors, and our summers here in Medford are dry. NOAA's 1991–2020 normals give 0.24 inches of rain in July and 1.25 inches across June, July and August.⁴ In the dry-climate column of the FHWA chart, lignin, asphalt emulsions and synthetic polymers all rate good, magnesium chloride rates fair and calcium chloride rates poor. In wet conditions, chlorides and lignin both rate poor.¹ Timing is covered in when to apply dust control, and getting the surface ready in how to keep dust down on a gravel road.