In response to your query,The following is from the
www.zainostore.com web site. Under the tips & tricks tab. I tried it and it works!!
Cleaning with Clay
Every car finish shares a common enemy: pollution. It relentlessly pursues your car from the second it leaves the factory until your car meets its ultimate demise. It's in the air we breathe, it's on the roads we drive, and it attaches to your car's paint, where it bonds and begins a process of oxidation.
When contaminants get a solid grip on your car's paint, washing alone may not be enough to remove them. Pre-wax cleaners also may not be able to exfoliate large particles. In this case, you have two choices: use a polishing compound, which removes a lot of paint material, or use Z-18 ClayBar. Clay isn't a polish or a compound, it is a surface preparation bar that smoothes the paint and exfoliates contaminants.
USES FOR CLAY
Clay is not a cure-all or a replacement for polishing. It's a tool for removing surface contamination. One of the many reasons for using clay is the removal of brake dust. Brake dust contamination, which attaches to painted rear bumpers and adjoining surfaces, is a metallic surface contaminant that can be removed safely and effectively by using clay.
Clay is also very effective on paint over-spray. If the over-spray is particularly heavy, you may want to seek the assistance of a professional. Tree sap and tar specks can also be safely removed with a clay bar.
Recently, I have also started using clay on my windows (exterior) to remove heavy road film, bug deposits and water spots. It works very well, and seems to outperform even the best window cleaners.