Why potholes come back every winter
A pothole is what is left when water and traffic carry a small, badly distressed piece of surface away. Caltrans' guidance on patching describes exactly that, and adds the part that makes them a winter problem: formation speeds up in wet weather, so they usually have to be filled while the hole itself is wet. What opens up is the visible end of an area that had already lost its strength.
The Valley gives them a season to work in. The NOAA normals for the Modesto airport put 1.07 to 2.57 inches of rain in each month from November to March, on 2.7 to 5.7 days a month that bring a tenth of an inch or more. Between storms the lot dries just enough for traffic to break the edges wider, and the next storm fills it again.
Filling the hole and repairing the pavement are two different jobs. A cold mix dropped into standing water deals with the immediate hazard and nothing else, and Caltrans is explicit that a patch placed in poor winter weather is likely to be of poor durability and should be treated as temporary. The lasting repair takes out the whole distressed area around the hole and replaces it with hot mix in the dry season. Both belong in the record, so a temporary fill is not later mistaken for a repair.
Holes open where the water sits and the wheels turn. Cracks that were never treated let water down into the base, and the crack treatment guidance follows that through to the weakening that produces them. On a lot with little fall, the water simply stays, which is why the same entrance and the same low corner come back on the list each year.
What pothole repair includes
The open hole is coned or barricaded and traffic routed around it on arrival, with any loose material lifted out, so the lot can keep trading while the area waits for its repair. Holes in a marked stall or an access aisle come first.
Every hole is located on the lot plan, measured and photographed, which gives the estimate an area rather than a number of holes and shows the pattern across the lot.
Where the weather rules a proper repair out, the hole is cleaned as far as it can be and filled with cold mix, compacted and marked as temporary.
In the dry months the area around the hole is saw cut square, taken out full depth, and any softened material below it removed before the new asphalt goes in.
Hot mix is placed in lifts against tacked faces and rolled flush while it is still hot.
Temporary fills stay on the plan as open items, so the next dry season starts with a list rather than another walk of the lot.
A winter fill buys time and nothing else. The repair that lasts is the whole distressed area cut out and rebuilt in dry weather, and every temporary fill is written down so it is not mistaken for one.
Where potholes open up first
Retail parking fields
Holes start at the aisle ends and the entry radius, where cars turn under power steering over pavement that already carries cracking.
Drive-thru and queue lanes
A lane where vehicles creep and brake in the same track all day wears a rut, the rut holds water, and the hole follows the next wet month.
Apartment entrances
The entry off the street takes every resident twice a day over a section that is usually the oldest pavement on the property.
School and church lots
Heavy use in short bursts over a long life, and a repair window limited to term breaks or the days between services.
Flat lots that pond
Where there is little fall, rain stands for days over the same low corner and finds every crack in it before it drains.
Packing and yard aprons
Field soil tracked onto the apron holds moisture against the surface, and heavy trucks on a light section punch through where it has softened.
Questions about pothole repair
Because the fill replaced the asphalt and not the reason it failed. Water reaching the material under the surface keeps taking support away, and each round of traffic lifts the new fill out again. Cutting the area out and rebuilding what is underneath is what stops the cycle.
It can, and in winter it often has to be, because a hole in a drive aisle cannot wait for a dry month. Caltrans treats a patch placed in those conditions as temporary, and so should the record of it. The permanent repair is booked for the dry season.
No. It addresses the immediate hazard. It is useful, it is quick and it keeps a lot open, but it is not a substitute for taking out the distressed area and replacing it with hot mix.
That depends on how much of it is failing. Scattered holes in sound pavement are individual digouts; holes appearing all along the wheel paths usually mean a larger area, and the survey says which of the two a lot has.
Cone the hole, keep vehicles off it, and photograph it. If it sits in an accessible stall or on the route between the stalls and the doors, mark it and keep that space out of use.
Pothole repair by city
Pothole work is requested through the asphalt paving page for your city, which covers the lots and rain months behind it.
Related asphalt paving services
