Can anyone explain what claybar is?
A clay bar is an elastic type of clay that is similar to modeling clay in how you can work it, but it's much more plasticky, and it doesn't come apart when it is wet. Most detailing clays come in medium to fine texture, which will need light polishing of the paint to remove the slight marring/dullness it leaves behind. There is also ultra fine clay, which does not require polishing after use. Finally, there is coarse or heavy duty clay, which has the coarsest texture, and is only used on paint that is in extremely bad shape, which also needs a lot of oxidation removal, which the coarser texture of the heavy duty clay facilitates.
Clay is used to grab embedded contaminants in the paint that cannot be removed by washing alone, and then pluck them out and absorb them into the clay, away from the paint. You also need a clay lubricant in order to use clay, because it allows the clay to slide across the paint surface. Some lubes work better than others. Lube should be used liberally and you should work small areas at a time, so that you don't waste lube by allowing it to dry out too fast on too big an area for you to work quickly enough. The clay lube also serves to prevent marring the paint with the contaminants you picked up during the claying process. Water alone is not an effective lube.
Detailing Clay was invented in the 1980's, by a Japanese company, I think.
Before clay, if there were any pieces of grit embedded in the paint that you couldn't wash off, then they would break loose during the polishing process, which would invariably cause harsh scratches in the paint, which would then require even more polishing of the paint in order to remove them.
I have found it best to use small pieces of clay at a time, and not the whole bar, because if you drop it, it's trash, unless you can carefully use a very sharp knife to slice off ALL of the area of the clay that touched the ground, to be sure to remove ALL grit that it picked up from the ground. Of course, you want to work in as clean an area as clean as possible, but there is almost always some dirt laying around.
As you use the clay and it gets dirty, you knead the clay so that you have a clean area to work with. Eventually, the clay will become so dirty that it should not be used on paint anymore, but could be ok to use on some wheels, so somewhat dirty clay can still be useful.
When you use clay, you want to glide it across the surface, and not actually rub with it, because that will increase chances of marring and streaking the clay. You can clay faster, but not rub harder, to make it go quicker. Just be careful not to fling the clay out of your hands working fast.l
If you do not use enough lube, then you will get smear clay on the paint, which has been mistaken as primer by some people. Often times, you can pick up some of this clay again by more claying, only with more lube this time. Otherwise, you will need to try some detail spray, waterless wash, polish, or solvent and a cloth to remove it.
Claying greatly increases the reflectivity of the paint if the paint has a lot of contaminants in it, because it makes the paint smoother and flatter, and a smoother and flatter area is always more reflective.
To test whether a car needs claying, you can feel it with your hands, or put your hand in a plastic sandwich bag, and see if it feels rough at all. If it feels rough, it needs clay. If not, no need to clay. Usually the horizontal surfaces of a car are the ones with the most embedded contaminants, and often only the horizontal surfaces need claying at all, because that is where the contaminants settle.
There is another use for clay, and that is overspray removal. Clay is the best stuff there is to remove overspray with, and the sooner you get to it, the better. If you get to it in a day or two, it's actually pretty easy to do, because the clay removes the overspray paint droplets which stick up from the otherwise smooth surface of the paint.
If the overspray is very severe, then perhaps the heavy duty clay is needed. Otherwise, if you remove the overspray in a day or two, (preferably immediately) the medium to fine grade will suffice, and perhaps even the ultra fine, although I have never used the ultra fine for that purpose.
Always start with the gentlest clay to see how it works, as you can always go coarser, but if you start out too coarse, you will make a lot more work for yourself.
Be careful with clay around rubber trim. It can leave a difficult to remove stain in just one swipe.
That is most of what you need to know about clay, other than actually doing it.
There is a lot to know about detailing before you have a full fledged business. Never do more than you are fully capable of doing on a client's car. Always practice on junk cars, junk parts from body shops, or your own cars until you PERFECT your technique.