In a nutshell: improperly hand washing can damage your car more than mechanical washing.
Many people wash their cars by hand. Some do it to save money, some just enjoy the process, and some do it to make their car look better and last longer. Many people wash their cars properly, but it is easy to miss or perform certain steps incorrectly. Hence, an improper hand wash can cause more damage than a mechanical wash.
Most hand washers fall short with equipment and/or products.
The average hand wash is done with a hose, 1 bucket, a sponge, and some old rags or chamois.
While the hose is no problem, a pressure washer removes more dirt prior to contact washing and thereby reduces the likelihood of scratching your paint.
Washing your vehicle with only 1 bucket also increases scratching as dirt removed from the vehicle is re-applied when the sponge enters and exits the bucket. Also, washing with a single bucket allows for cross-contamination between the wheels and paint.
Even when combined with the proper chemicals, only the highest quality sponges keep your car safe from scratches. Most sponges, however, don’t absorb dirt and instead drag it across the paint leaving tiny scratches.
For drying cars, rags and leather chamois are similarly problematic in that they drag dirt across paint rather than lifting it away.
Average hand washes are typically done with the cheap chemicals found lining the shelves of most auto-parts stores.
Some of these chemicals are much like those used in mechanical washes in that they are too strong.
The over-strengthening of products is largely a result of consumers’ misunderstanding of what makes a “good” product. For example, some acidic wheel cleaners that can be sprayed on and hosed off to reveal a super shiny wheel are “good” because they reduce the consumer’s overall cleaning effort. However, such convenience will come at the cost weakened wheel finishes. Hence, most pros and enthusiasts prefer “weaker” soaps, cleaners, or iron dissolving cleaners that require one to manually agitate the dirt in some way.
Excessively aggressive products exist for all of your vehicle’s surfaces. It is best to buy products from a company that specializes in car care chemicals.
To significantly reduce the likelihood of scratching your car, click to learn the basics of a proper wash.