Basic Color Sanding
Posted by Jay Schneider. Filed under Paint.
December 19, 2011
In searching for the best information on color sanding, it is fascinating to me just how many sources of information there are really out there. Much of it is good and others are not. I found an article written by Chris Baylor from the Woodworking Guide that does a great job explaining the basics. I would like to credit him and interject where I may when it pertains to automotive color sanding.
The first step to finishing any automotive paint project is called color sanding. Whether you choose to power sand or to sand by hand you need to select the right type and grit of sandpaper. Sanding with the wrong sandpaper could irreparably damage your handiwork.
Choose the Right Grit:
Abrasive paper is graded based upon the number of abrasive particles per square inch that make up the sandpaper. The lower the number, the more coarse the grit. Sandpapers are commonly graded as coarse (40-60 grit), Medium (80-120), Fine (150-180), Very Fine (220-240), Extra Fine (280-320) and Super Fine (360 and above). Sanding with progressively finer grits removes the scratches left by the previous paper and eventually leaves a smooth finish. Typical color sanding in the automotive industry starts somewhere in the 1200-1500 grit area, and can go as high as 4000 grit or higher!
You might be asking, "Why can't I just sand the entire project with Super Fine sandpaper?" Well, there's nothing saying that you can't. However, coarse grit papers will remove material fast, and when followed by finer grit papers, makes for much easier and quicker sanding.
There are two primary types of sandpaper: commercial grade and industrial grade. The differences lie in a few areas, namely the material used as the grit, the backing material (paper or Mylar) and the adhesive used to hold the grit onto the paper. Industrial grades use higher quality materials for all three components.
Additionally, you may see sandpapers that are rated as either "open-coat" or "closed-coat". The difference is that closed-coat sandpaper has the grit particles grouped more closely together, where open-coat sandpapers have larger gaps between the particles. As a general rule, open-coat is typically better for woodworking, as it clogs less often, particularly when working with softwoods that contain more resin.
Types of Abrasives:
There are five main types of sandpaper available, but not all are conducive for color sanding. Glasspaper, also known as flint paper, is very lightweight, typically a pale yellow color. Glasspaper disintegrates easily, and is rarely used for color sanding.
Garnet paper is usually a brownish-red color, which is commonly used in woodworking. It will not sand wood as quickly as other sandpapers, but leaves a better finish. Garnet is an excellent choice for finish sanding.
Aluminum Oxide is another common type of sandpaper for woodworking and automotive projects. It is the type of paper most often used in power sanders. Aluminum Oxide is more durable than Garnet paper, but doesn't leave as nice of a finish.
Silicon Carbide paper is typically a dark gray or even black. This type of paper is used primarily for finishing metals or for "wet-sanding", using water as a lubricant. . The term wet sanding, is a reference to sanding whereby water is used help flush away surface contaminants which would eventually scratch the surface and plug the papers surface.
Finally, Ceramic sandpaper is made of some of the most durable abrasives available, and can remove considerable amounts of material in a hurry. I like to use it where body fillers must be used. Ceramic paper is often used for sand paper belts and drum sanders. It will usually leave a very rough finish, so exercise care when using Ceramic sandpaper because it can quickly sand through the finish layer.
Next up? Sand Paper dissected.
Keep the blue skies up and Happy Motoring!
Scott S. Mc Lain
Lake Country Mfg.