White residue may be related to moisture movement. Ask for a moisture and substrate assessment before treating it as only a cleaning issue.
Document before covering
Photograph the affected area, note whether it changes after rain or vehicle use, and avoid applying a quick-fix product before an evaluation. A clear record helps a provider separate cosmetic cleanup from a preparation or repair requirement.
Ask for a written response
Request a plain-language explanation of the condition, the recommended preparation or repair, what will remain visible, and how the decision affects price and schedule. A coating should not be sold as a fix for a problem that has not been diagnosed.
Related guidance
Review concrete moisture, joints and cracks, and diamond grinding.