Listed in Road Maintenance
Overlaying an existing road with a fresh layer of asphalt is a common and cost-effective maintenance technique. However, there comes a point when adding yet another layer without milling (grinding) the surface first can lead to more harm than good. Milling is the process of removing a portion, or all, of the existing pavement before laying new asphalt. This article explains how to recognize when it’s time to mill and why milling may be necessary before repaving.
Why Milling May Be Necessary
1. Avoiding Height Buildup
Each time a layer of asphalt is added, the road surface gets higher. Over time, this can:
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Create drainage problems, causing water to pool on the road surface.
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Reduce curb reveal, especially important for ADA compliance and effective stormwater control.
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Cause transitions at driveways, intersections, or bridge decks to become uneven or hazardous.
2. Improving Surface Bond and Longevity
New asphalt adheres best to a clean, uniform surface. If the old surface is oxidized, cracked, or uneven:
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Milling removes the top layer of damaged or brittle pavement.
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It improves the bond between old and new layers, preventing slippage or delamination.
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Milling also eliminates reflective cracking (when existing cracks quickly reappear in the new surface).
3. Correcting Surface Irregularities
Milling is essential when:
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The road has rutting (wheel path depressions) that would carry through to a new surface.
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There's a need to restore proper cross slope and elevation.
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The surface has settled or heaved in ways that can’t be corrected with overlays alone.
Signs It’s Time to Mill Before Repaving
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Pavement Has Been Overlaid Multiple Times: If your records show two or more prior overlays, milling should strongly be considered before the next round.
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Poor Drainage or Standing Water: Water pooling along curbs or at low points indicates the surface is too high or uneven.
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Cracking That Keeps Coming Back: Recurrent block, alligator, or longitudinal cracks mean the damage lies deeper than the surface and must be removed.
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Height Conflicts with Structures: If the road surface is nearly level with curbs, manholes, or bridge joints, milling will help reset proper height differentials.
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Localized Distress or Raveling: Patches of loose aggregate, potholes, or raveled areas signal that the surface is too degraded to support a new overlay.
How Deep Should You Mill?
That depends on the objective:
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Surface Milling (1" - 2"): Used when minor surface issues exist or to improve smoothness and bonding.
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Intermediate Milling (2" - 3"): Removes surface and some base issues; good for moderate rutting and cracking.
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Full-Depth Milling (more than 3"): Required for severe structural damage or to reset road grade entirely.
Milling isn’t always necessary—but skipping it when it is needed can shorten the life of your overlay, increase drainage issues, and raise long-term maintenance costs. A proper road assessment, including visual inspection, grade measurements, and a review of past maintenance history, will help you determine whether milling should precede your next repaving effort.
Need Help Managing Road Maintenance History?
With Roadwurx, you can track paving dates, overlay history, and surface conditions for every road segment in your town. Visit https://roadwurx.com to learn more.