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.
 

Surface contamination, as shown by this diagram, are difficult to clean or polish off, yet paint cleaning clay removes it with ease.

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 a clay bar.  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 quickly and easily 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.

These are the two most common retail kits available.  On the left is the Meguiar's Quik Clay kit, which includes a bottle of their popular Quik Detailer detailing spray and a fine grade clay.  On the right is the Clay Magic Perfect Finish kit, which includes a soap-based lubricant and fine grade 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.

EVALUATING YOUR PAINT
How do you know if you need to use a clay bar?  After thoroughly hand washing your car, feel the surface of your car's paint.  Do you feel bumps and rough spots?  These bumps are contaminants attacking the finish of your car.  Removing these surface contaminants (road tar, acid rain spots, bug residue, paint over-spray, brake pad dust, hard water spots, etc.) will improve both the look and health of your car's paint.  By the way, you can magnify your sense of touch by inserting your fingertips into a sandwich bag or a piece of cellophane.

No matter how well you hand-wash your car, many of the contaminants that have worked their way into your car's paint finish will remain.  Have you ever looked at your foam wax applicator pad after applying a coat of wax?  What do you think that black stuff is?  It's dirt, and you're waxing over it, sealing it in.

CLAY SAFETY
Detailing clay isn't new.  Paint and body shops have been using it for years to remove paint overspray.  Clay is fairly new to the car detailing market, and is very new to the consumer on retail shelves.  In the early days there was always a concern that paint damage might occur if improperly used.  

New technology detailing clay bars are made of fine polishing particles in a soft, malleable "clay" medium that allows the bar to be formed and kneaded.  Some clay makers add color to make the bar more attractive or to identify bars of differing strength (coarseness).

Many clay products claim to contain no abrasives.  This is stretching the truth.  The reason clay manufacturers claim their products don't contain an abrasive is because the general public thinks the word "abrasive" refers only to aggressive, paint removing materials.  The fact is that the abrasives in most automotive clay products are so fine that you will not see any reduction in paint gloss.  After several uses, paint luster may even improve.

Still, I have heard some horror stories about people ruining a Ferrari paint job using a clay bar.  I can see how this might be true if an inappropriate product was used or if the clay bar is used incorrectly.

USING CLAY
Using clay is very easy, but you must follow the instructions.  Use clay incorrectly and you will create a mess or scuff the surface of your paint.

Before using detailing clay, you must thoroughly clean and dry your car to remove any loose dirt.  Direct sunlight should not fall on your car's surface, and it's best if the work area is relatively cool to prevent rapid evaporation of the clay lubricant.

To use the clay bar, you spray a lubricant on a small area of your car and rub the clay back and forth with light to medium pressure.  If the lubricant begins to dry, you'll need to spray more.  Clay is fairly sticky and cannot be used dry.  Try using clay dry and you'll make a big mess and scuff your paint.

After a few passes with the clay, rub your hand over the area you cleaned to check for areas missed.  You should feel a distinct difference between the areas you have clayed and the areas you have not clayed.   Keep rubbing until all contamination bumps are gone.  Finally, wipe the clay residue off with a soft microfiber towel, and buff to a nice luster.   Just like waxing, work in small areas.

Check the clay bar frequently for hard particles.  When found, pick them off.  Make it a habit to occasionally knead and reform the bar so that a fresh portion of the bar contacts your car's paint.  If you drop your bar of clay on the ground, it's history.  Toss it out.  Don't take any chances, discard the clay bar if it becomes impregnated with grit.  Read the manufacturers' directions for the number of uses of their clay bar.  Do not overuse a clay bar.

When you're finished claying your car, you should wash it to remove the lubricant film, then go over it with a pre-wax cleaner to finish cleaning the paint.  Finally, seal your freshly cleaned paint with your choice of wax or sealant.

OTHER USES FOR CLAY
Clay isn't just for paint.  You can use detailing clay on any smooth, hard surface, including glass and chrome.  Do not use clay on clear plastic, such as headlight lenses.

When I can no longer remold clay to get a clean surface, I retire it for use on my windows.  The dirty clay will not harm glass, and it's amazing how much dirt film clay can remove from your exterior glass windows.

I also use my old clay to clean wheels.  Clay will safely remove stubborn, embedded brake dust, tar and road film from all factory wheels.  Clay is not recommended on wheels that do not have a factory clearcoat or powder coat finish. 

CLAY FACTS
Over the past four years I have received a lot of email questions regarding clay.  Here are some common questions and answers:

Q1. I dropped my clay on the ground.  Can I still use it?
A1. The safe answer is no.  Clay will pick up small particles of grit from the ground that will scratch your paint.

Q2. If I use clay do I still need to polish my paint?
A3. Yes.  Clay will not remove swirl marks, scratches or etching from acid rain or hard water spots.  Paint polish is still required to remove these paint defects.  If your paint is new or like-new, detailing clay will significantly reduce the amount of polishing required to keep your paint in good condition.

Q3. What is the best clay?
A3. What label do you like?  There are only a couple manufactures of clay, and the technology is protected by U.S. patents.  Clay is manufactured with different levels of abrasiveness and colors to suite different applications.  There are some subtle difference in technology (plastic vs. elastic material) and the firmness of the material.  In general, softer clays are safer and easier to use.  A firm clay cleans better with a little more risk of scuffing or scratching.

Q4. Is it better to use soapy water or a spray lubricant?
A4. Both work equally well.  If you want to do the job fast, use a bucket of soapy water.  If you want to work inside or do a thorough job, use a spray lubricant.  With a spray lubricant you can wipe down each panel as you go and feel for areas you missed.

Q5. How do I store my clay?
A5. If your clay did not come with a re-usable plastic container, store it in a plastic Ziploc bag.

Q6. Will clay remove my wax?
A6. In most cases, clay will "scrub off" wax protection.  Some paint sealants are hard enough to withstand being cleaned with clay, but most are not.

Q7. Is it safe to clay using my buffer?
A7. Detailing clay was not designed for machine application.  Even so, there are a couple foam buffing pads designed to hold a waffer of clay.  These systems work with the Porter Cable 7424 dual-action system.  The risk of paint damage is too high to be worth any potential time saving benefit. 

SUMMARY
Automotive paint cleaning clay offers many advantages in the removal of surface contamination from paint.  Even in the hands of a first-time user, clay is safe and easy to use.   Sure, if you use a dirty clay bar, scratches can result.  However, compared to machine buffing, compounding, or using harsh chemicals, clay is safer, faster and easier.