No matter how frequently you wash your vehicle or what brand of soap you use over time your vehicle will become contaminated with all kinds of different particles such as..
Rail Dust (little yellow dots all over your paint that look like rust spots)
General Air Pollution (exhaust fumes etc.)
Tree Sap Mist
Over time these contaminants build up and become embedded on the paint surface making it look dull & feel rough. Even worse, if neglected for a long time metallic particles such as rail dust & brake dust can work their way deep into the paint. If these particles come in contact with the bare metal of the vehicle it is an access point for moisture which will lead to rust. Because contaminant build up is a gradual process many people don't even realize or notice it is occurring. You may just think you are due for a waxing when the paint loses it luster. However if your car is contaminated waxing over it means you are just waxing over dirt and the results will not be what they should be.
As a matter of fact many waxes sold in "big box" retail outlets contain detergents & cleaners that will remove some contaminants while you wax. Have you ever been applying a wax to your car and looked at the foam applicator pad and it was black? That is because you are removing dirt as much as you are applying wax. The wax manufacturers know that most consumers are not knowledgeable enough to decontaminate first so they include cleaners in the wax. A lot of the shine you see when the job is done is not the wax itself, it is because you were removing contaminants and cleaning the paint while you waxed. There is nothing wrong with cleaner waxes but there is a trade off. You will not remove as many contaminants as you will decontaminating separately, and the wax may be as high quality as one that contains no detergents.
There is very simple way to tell if your vehicle is contaminated. Take a plastic bag (a grocery bags work great) and run your fingers over the paint with the bag in between. If the paint feels rough or bumpy, it is contaminated.
Regardless of the contaminates you are trying to remove you should clay bar every 6 months to keep your paint nice and smooth. However if there are specific problem areas you need to tackle you may want to supplement your clay barring with a chemical solution specific to that problem. For example if your car is covered in rail dust using an iron & fallout remover specifically designed for that issue before you clay bar will speed up the process a lot and will remove the contaminants in tight areas (around emblems, license plates etc.) that are tough to get at with clay. If you have a lot of tree sap on your paint use a dedicated tap sap remover, or a tar remover for tar etc. then clay bar to remove the remaining contaminants.
There are 2 type of clay bar...
Traditional clay comes in a malleable bar (almost like "silly putty") To use it you break a piece off the bar, flatten it with your fingers and rub it over the paint surface. In order for the clay to slide over the surface you need a lubricant spray. There are complete clay bar kits available that include the clay & the lubricant or you can purchase each individually.
As you rub the clay over the paint the contaminants are trapped in the clay. As an area of the clay surface gets dirty you can simply fold the clay to a clean section and continue on. Once you cannot find a clean section of clay its time to get a new piece. If you drop the clay DO NOT use that piece again. It will pick up particles of dirt from the ground that will scratch your paint.
If you have purchased clay on its own or the lubricant in your kit runs out before the clay does (many kits come with multiple bars of clay) you can purchase a dedicated clay lube separately or most detail sprays work quite well as a clay lubricant. Note: If you are purchasing a detail spray just to use as a clay lube there is no point in getting one with added polymers etc. They generally cost more and you don't need those gloss enhancers if you are just using the product as a clay lube. Some of our favorite clay lubes are..
Synthetic clay contains a polymerized rubber surface. They are available in several formats (mitts, towels etc). Unlike conventional clay as you rub this rubber surface on the paint it breaks away the contaminants as opposed to trapping them.
There are several advantages of synthetic clay over bar clay...
Synthetic clay lasts about 4 X as long as regular clay. You will get enough clay in a $30 - $35.00 clay bar kit to clay approx. 4 - 5 cars. A $35.00 clay towel is good for about 20 uses.
Synthetic clay works very well with standard car wash soap as a lubricant (no special lubricant needed)
If you drop synthetic clay on the ground you can rinse it off and reuse it.
There is no right or wrong regarding which type of clay to use. Because traditional clay is very sticky you may find it grabs (removes) more deeply embedded contaminants than synthetic. Which one you pick may depend on the goal you want to achieve. If you are clay barring before applying a long life ceramic coating you might want to use a traditional clay to make sure that your paint is as clean as possible. If you frequently wax your car having a synthetic clay handy allows you to quickly decontaminate the paint after your pre-wax wash before each wax job.
One final product worth mentioning that is very inexpensive, handy and easy to use is SM Arnold's Sure Scrub 2. Although not as deep cleaning as a clay solution this product can be used periodically after your car wash (use it with car wash soap) to help remove contaminants. It also works great on bugs and if used along with a chemical iron remover helps to remove rail & brake dust quicker (you use less product).
No matter which option you choose, regular decontamination of your vehicle will greatly enhance your paint's appearance and help your wax, sealant or coating bond better and last longer!