Our cars take a daily beating from bad roads, bad drivers and exposure to the elements (rain, sun, salt, bird droppings, pollen). Yet 52 percent of us wash our cars less than once a month, and 15 percent never wash their cars at all, according to a survey by the International Carwash Assn.

Regular (as in weekly) car washings are for more than appearance’s sake. Taking care of the exterior finish will prolong a car’s life and protect its resale value. Scott Martindill is owner of Mobile One Services, an auto-detailing service in suburban Maryland. He has tips for an at-home washing this weekend. Better yet, tonight.

¢ How often: “Generally speaking, a car needs to be washed every week to two,” says Martindill. “At the very least, washed and waxed every six to 12 months. Bare minimum.” If the car is exposed to lots of snow or pollen, if it’s parked outside or driven long distances, wash more often. “If you only wash your car once a year, you’re shortening the lifespan of the paint.”

¢ Cleaning basics: Car-washing detergent (available at auto stores, hardware stores and big-box chains such as Target), a thick lamb’s wool carwash mitt and plenty of water. Dish soap or household cleaners can dull paint and strip wax. A carwash mitt will catch and hold onto dirt instead of dragging it over the finish. “You’re much more likely to scratch the paint if you use a sponge,” he says.

¢ When and where: Early in the morning or late afternoon in a shaded area is best. If you wash in the midday sun, use lots of water and rinse often to avoid the soap drying on the paint, which will leave a film on top of the paint and make the car look dingy and splotchy.