Urban fallout is full of nasty particles and chemicals that can attack a vehicle's paint, but some of the worst things that fall onto our cars and trucks have nothing to do with industrial or city pollution.
Tree sap is among the toughest contaminants to remove from a vehicle's finish--and among the most damaging.
I recently was asked by a reader in Palos Verdes, "How do I get the sap off my car?" It's actually a serious and hard-to-solve problem that can cause costly damage to a vehicle if left unattended.
Trees literally spray out sap. A lot of people like to park under trees to keep their vehicles in the shade, figuring it's good for the paint. But the damage caused by sap--particularly pine sap--is greater and longer lasting than the benefits provided by shade.
Once tree sap bakes onto a vehicle under a hot sun, it become like a resin, says Gary Silvers, vice president of research and development at Irvine-based Meguiar's Inc., the auto care and wax company. You can often see the sap as clear or reddish bumps that feel rough to the touch.
After baking into the finish, the sap eventually etches into the clearcoat and paint, causing webs of deterioration around every spot of sap.
Baked-on sap will not wash off, and even many solvents won't take it off. Hard sap shrugs off virtually all combination cleaner waxes, not to mention spray cleaners. The conventional way of dealing with sap is to use a polishing or rubbing compound. This takes off the sap but also a layer of the clearcoat or paint, causing swirl marks that are quite pronounced in darker colors. Among professionals, a rubbing compound is a last resort, something akin to dermabrasion of human skin.
About five years ago, the automotive wax industry began marketing to consumers a new system--clay bars--to remove tree sap and other contaminants that embed themselves into paint. Meguiar's and Huntington Beach-based Mothers are two leading manufacturers with clay bar systems on the market.
"Detailers have used clay bars for years," said Craig Burnett, a chemist at Mothers. "They are the secret of detailers."
But few consumers buy or even know about clay bars. To use the product, you spray on a cleaner--typically a detailing fluid--to provide lubrication for the bar of special clay. You then rub the bar lightly across the paint.
The clay adheres to the sap or other contaminant, pulling it away from the vehicle's surface, somewhat akin to pulling lint off a sweater with tape. Eventually, the clay bar itself becomes contaminated and must be discarded.
Clay bars can also remove metal particles, paint overspray, brake dust and other gunk that attaches itself to the paint. Burnett says paint overspray is a huge urban problem, because outdoor paint spraying can damage cars hundreds of feet away.
I've used a clay bar with impressive results. Afterward, the paint feels remarkably smooth and takes wax extremely well. The downside is that clay bars are not a quick fix. Sap and other contaminants often take repeated passes to remove.
It's probably best to do a hood or trunk lid in one session for 15 minutes and then come back to another section on another day. The good news is that contaminants such as sap usually attach only to horizontal surfaces.
In addition to clay bars, manufacturers still sell cleaners designed to remove sap, tar and bugs. Turtle Wax, the largest auto wax producer, sells such a product. I've tried it and it does work moderately well, though it's even slower than clay bars and in my test failed to remove particularly hard deposits.
Michael Schultz, director of product development at Turtle Wax and a former chemist, says the company's product contains the three key solvents for most grime: turpenes, glycol ethers and petroleum distillates. Turpenes are derived from pine trees, so it should theoretically dissolve pine sap, but only if it has recently fallen on the paint. Turtle Wax also makes a professional clay bar system for the detailing trade.
Other companies' clay kits cost $10 to $15 and include detailing spray, a small clay bar and, in some cases, a small amount of wax.
Ralph Vartabedian cannot answer mail personally but responds in this column to automotive questions of general interest. Please do not telephone. Write to Your Wheels, Business Section, Los Angeles Times, 202 W. 1st St., Los Angeles, CA 90012. E-mail: email@example.com.