What is a mill and overlay?

A mill and overlay consists of removing the top layer of pavement, usually 1 to 2," and replacing with new pavement. This process usually happens in 5 steps as follows:

  • Step 1: Remove the old pavement (milling)
    • During this step, the top layer of pavement (1-2") is ground off the road by a milling machine. The ground off pavement "millings" are trucked back to the pavement plant to be recycled and used in future pavement. It generally takes only an hour or two to complete the milling process unless the street is very wide and/or a long segment of the street is being milled.
    • Generally, the street will remain open to traffic during the milling process, but a flagging crew may be directing traffic around the construction operations. The street surface is safe to drive on when the milling process is complete, but you will probably notice that the pavement surface is much rougher than before.
  • Step 2: Replace curbs and drainage inlets that need replacement
    • After the milling process is complete, the city's Public Works Department crews will replace any curbs that have sunk over time and are collecting water and/or any drainage inlets that are damaged or disintegrating. Replacing a drainage inlet takes up to a day to complete, and any concrete curb replacement takes about a week to cure before new pavement can be put down next to it. The street will be open during this work, but parking may be limited to allow for work crews to access the replacement sites.
  • Step 3: Replace any affected pedestrian curb ramps with ADA-compliant ramps
    • Due to the Americans with Disabilities Act (ADA) and the City's ADA Transition Plan, all non-compliant pedestrian ramps that connect to a crosswalk that is affected by a Mill and Overlay project will be replaced with ramps that meet ADA requirements. Generally, pedestrian access to these ramps will be limited for a few days to remove the old ramp, regrade the ramp area, pour a new ramp, and let the concrete harden enough to walk on again. The streets will be open during this work, but flaggers or other traffic control may be present while the ramp construction is occurring.
  • Step 4: Adjust manhole covers
    • Manhole covers that are too far below the pavement surface will be adjusted higher to match the new pavement surface. We will also replace the adjustment rings on manhole structures if they are falling apart. You will probably notice that the manhole covers will be sticking out of the ground at this time. That is on purpose because the manhole covers need to match the final pavement surface, which is about 1-2" above the temporary (milled) surface. The streets are generally open to traffic during the adjusting operations, but flaggers or other traffic control may be needed during the adjustment construction activities.
  • Step 5: Replace the pavement (overlay)
    • The final step of a Mill and Overlay project is to actually pave the new street surface! Before the new pavement is put down, a layer of glue (called "tack") is applied to the street surface to stick the new pavement to the old pavement. It is ok to drive on the tacked street before paving, but please drive slowly to avoid any splatter of the tack on your car. It is really hard to remove tack from the outside of your car once it gets on there!
    • The paving machine follows a few minutes behind the tack truck and lays down a fresh batch of pavement. Rollers follow closely behind to compact the new pavement to provide a solid surface to drive on.
    • You won't be able to drive on the new pavement until the crews are done rolling the pavement, which can take a half-hour or so from the time the paver goes by. Flaggers will direct traffic around the paving operation until the rollers are finished working on the pavement.

Show All Answers

1. What is a mill and overlay?
2. When can I drive on the new pavement?
3. Can I get in and out of my driveway while they are milling or paving?
4. Why does the city do mill and overlay projects?
5. Why do some cracks show up again soon after a mill and overlay?
6. Can you mill and overlay any street?
7. How is parking affected by mill and overlay projects?
8. How are mill and overlay projects paid for, and am I assessed for them?
9. Where and when is the city panning