Sandpaper Tech

Getting A Handle On Sandpaper

If you think the sandpaper on your garage shelf looks dated, consider the origins of sandpaper way back in at least the 13th century, when it is believed to have been invented by the Chinese. Sandpaper was created to rework and improve irregular surfaces, but it has done so much more. Sandpaper has taken on many forms over the past one thousand years, based on availability of raw materials, and how advanced a given society has been.

The word "sandpaper" tends to be a misconception because it isn't always paper. Abrasives are applied to all kinds of medium depending upon intended use. It can be fabric, paper, fiberglass, and more. When you look at sandpaper for what it is, it is rather crude with a bunch of grit applied to a glue-clad piece of paper. Grit is designed to remove material; be it paint, metal, body filler, lead, rust, and the rest of it. Huge teams of gritty particles go after the stuff we want to remove. Sandpaper is designated by how gritty it is or how much grit exists in a square inch. In other words, the grit number is a measure of grit population. The higher the number, the more grit we have in a square inch. A piece of 40 grit sandpaper has fewer grit particles per square inch than a sample of 600 grit paper. The 40 is coarse - real coarse when compared with 600 or 1000 grit.

If you want to remove paint or rust, you want a sheet of 40 or 80 grit paper, which will get you right down to the surface in short order. By the same token, if you'd like to rough up a surface for good paint adhesion, you want 320 or 400 grit paper. And for someone color-sanding paint, for a dipped-in paint look before final rubout, you want something super fine like 2000 grit. Use water as a lubricant, which is nearly like copy paper. It dulls the surface before a rubout with compound.

As important as the grit number is the coating - open coated or closed coated. Open coated sandpaper allows debris to collect between the grains of grit where closed coated does not. Another important issue is the type of grit. There are at least four basic types - Aluminum Oxide, which works on everything; Silicon Carbide for everything but wood; Ceramic, for wood only; and Garnet, for wood only. Grit used is on the back of your sandpaper.

Aluminum Oxide's advantage is it works with everything and is renewable as you work with it. It outlasts every other type of abrasive. Silicon Carbide is a harder abrasive than Aluminum Oxide yet doesn't last as long in heavy use. Ceramic is the hardest abrasive used most often to remove the toughest material. It is generally very coarse. Garnet is the softest abrasive and works quite well for finish work. It wears out quicker.

Choosing the right sandpaper is a matter of knowing intended use going in. You have two basic grades of sandpaper to choose from: commercial or industrial grade. Of course, industrial grade is more expensive than commercial because it is more durable and worth every penny because you get better materials. This is why you want to source your industrial grade sandpaper from a professional auto body supply store. Your sanding efforts should generally begin coarse and progressively get finer as you go along to achieve an acceptable finish. For paint and rust removal, we begin with 40 to 80 grit, yet it is best to stop the minute metal appears. Prep work calls for 240 to 320 grit. Final finish work once primer and filler are down is 400 grit wet.

Simi Automotive Paint & Supply (805) 526-3882 - Eastwood Company (800) 343-9353

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