Does auto insurance cover sand damage?

Assuming that you are referring to physical damage to the vehicle, the analysis will depend upon the dynamics that caused the sand to damage the car.

For example, while it is unlikely that the collision coverage will come into play, the comprehensive coverage may. An example of comprehensive coverage being triggered to compensate you for property damage for a sand-related occurrence is if the car were left outside and a windstorm or similar occurrence blew a quantity of sand against or into the car resulting in sheet metal/exterior finish damage.

Without more information as to the dynamics of the occurrence, a more complete analysis of potential coverage cannot be given.