Q. I am wondering about standards for fixing potholes. Is there a minimum height for the pile of repair tar and gravel (knowing that it will compress over time)? Are some holes deemed too large for filling (requiring a different repair method)? Does water in a hole cause a problem for repair?
A. The city uses two pothole-repair mixes:”cold patch” and “hot patch.” Both consist of asphalt, adhesives, and gravel. Hot patch is superior but because it is installed at very high temperatures (about 300*F), it can’t be used in the winter.
Cold patch is generally considered a temporary fix, although improved formulations are continually developed. It is piled above the road surface to allow for compression over time; while there is no minimum height, too thick an application can slow curing and hardening. The ideal thickness is about two inches.
Some cold-patch recipes have trouble with dilution from water in the hole, but other cold-patch products are made with polymer adhesives that can handle water. Ann Arbor reports that its cold-patch mix can handle water. However, cold patch can suffer from the same freezing and thawing cycles that created the pothole, so reapplications may be required.
Sometimes the hole is too big for cold patching to be effective. It may be applied anyway to make the road usable until the weather warms enough to make a permanent repair with hot patch.
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