Mill and fill, explained

Mill and fill is exactly what it sounds like. A profiling machine mills the existing asphalt surface off to a set depth, the millings are loaded out, the exposed surface is cleaned and tack coated, and a new layer of asphalt is placed and compacted in the space that was removed. The finished level matches what was there before, which is the point: kerbs, drainage, line marking and driveway crossings all stay where they were.

It is the workhorse of pavement rehabilitation because it treats the part that has failed without disturbing the part that has not. A surface that has rutted, cracked or ravelled can be replaced at 40 or 50 millimetres while the base underneath, which is usually still sound, stays in service. Compare that to a full reconstruction, which means closing the road, digging out the lot and rebuilding from the subgrade up.

The constraint is almost always the environment rather than the work. A carpark has to keep trading. An intersection has to keep moving. A resort road has six weeks between the last of the snow and the first of the guests. So mill and fill jobs tend to be staged, shifted, split across visits and run at night, and the planning is where the job is won or lost.

Where profiling is all that is needed, it can also stand alone: milling to correct levels or shape ahead of another contractor's surfacing, removing a failed section for patching, or taking off an old surface before a full overlay. We do it either way.