“Mill and overlay” comes up in nearly every conversation about resurfacing a commercial parking lot, but property owners are not always sure what milling entails or why a contractor recommends it over a simpler overlay. This guide breaks down the process step by step and explains when it is the right call for a commercial property. Note that this guide is focused specifically on mill-and-overlay as a paving contractor’s resurfacing method, not on buying or selling recycled asphalt millings as a standalone material, which is a different topic entirely.
What Is Asphalt Milling?
Milling is the process of mechanically grinding off the top layer of existing, worn asphalt using a specialized milling machine equipped with a rotating drum lined with carbide teeth. Rather than applying a new layer directly over a damaged surface, milling first removes the deteriorated material, leaving a clean, textured, and level surface for the new asphalt to bond to.
The Mill-and-Overlay Process, Step by Step
- Site assessment. A contractor evaluates the existing pavement’s condition, drainage, and traffic patterns to confirm the base is structurally sound enough to support resurfacing rather than full reconstruction.
- Milling. The milling machine grinds off a set depth of the existing asphalt, commonly one to two inches for a standard commercial resurfacing project, though depth varies based on the specific pavement’s condition and design.
- Material removal and recycling. The ground-up material, known as reclaimed asphalt pavement, is collected and hauled away. This material is highly recyclable and is commonly reprocessed into new asphalt mix, which reduces both landfill waste and the amount of new raw material needed for the project.
- Surface preparation. The milled surface is cleaned of debris and dust, and a tack coat is applied to help the new asphalt layer bond securely to the underlying milled surface.
- Paving the new overlay. Fresh hot-mix asphalt is laid over the prepared surface and compacted with rollers to achieve proper density.
- Striping and cure time. Once the new surface has cooled and cured sufficiently, striping is applied, and the lot is reopened to traffic.
Why Milling Before Overlay Matters
- It preserves existing grades. Because milling removes material rather than adding it, curb lines, drainage slopes, and door thresholds stay close to their original elevation instead of rising with every overlay applied over the years. A parking lot that has been overlaid repeatedly without milling can eventually create drainage problems at curbs and building entrances.
- It removes surface defects at the source. Cracking, rutting, and oxidized, brittle asphalt are physically ground away rather than left in place to telegraph through the new surface as reflective cracking within a season or two.
- It recycles material responsibly. Milled asphalt is one of the most recycled materials in the construction industry. Reclaiming and reusing it reduces both project waste and the volume of new raw asphalt binder and aggregate required.
- It creates a stronger bond. A freshly milled surface, combined with a properly applied tack coat, bonds more securely with new asphalt than an old, weathered, and oxidized surface would on its own.
When Mill-and-Overlay Makes Sense
Mill-and-overlay is a strong option when:
- Surface distress is significant (widespread cracking, oxidation, moderate rutting), but the base and sub-base underneath remain structurally sound.
- Existing curb heights, drainage grades, or door thresholds cannot tolerate the elevation increase that would come from a non-milled overlay.
- The pavement has already been overlaid once and cannot support another layer without creating drainage or clearance issues.
When Mill-and-Overlay Is Not the Right Fix
Milling and overlaying a structurally failed pavement simply buries the problem under a new surface that will fail again, often within a year or two. Signs that a lot needs full reconstruction rather than resurfacing include:
- Deep, recurring potholes that return in the same locations after repeated patching.
- Large areas of alligator cracking that extend through the full pavement depth, indicating base failure rather than surface wear alone.
- Visible sub-base instability, such as pumping (water and fine material being forced up through cracks under traffic load).
- Significant, uneven settling across large sections of the lot.
Frequently Asked Questions
How deep is a typical milling pass?
Most commercial resurfacing projects mill between one and two inches of existing asphalt, though the exact depth depends on the pavement’s condition and the overlay thickness being applied. A contractor determines this during the site assessment, not with a one-size-fits-all number.
How long does a milling and overlay project take?
For a standard commercial parking lot, milling and paving can often be completed within a few days, though the exact timeline depends on lot size, weather, and whether the property needs to remain partially operational during the work.
What happens to the milled asphalt?
It is collected as reclaimed asphalt pavement and typically recycled into new asphalt mix, either for this project or a future one. This is one of the more sustainable aspects of commercial paving work.
Not sure whether your lot is a good candidate for mill-and-overlay or needs a different approach? Contact American Pavement Solutions for a free assessment, or learn more on our pavement resurfacing services page.