Smooth Talk Page 2
Open and closed
The backing should also say whether the paper is open or closed coat. Closed coat is more common and this means that the entire paper surface is covered with abrasive. Open-coat paper has about 40 percent of the paper covered with grit, so even though the grit is the same size, there is less of it on the sheet. The extra space between the grit provides room for sanding dust, which makes open-coat paper less prone to loading, where sanding particles become trapped in the paper. Open-coat paper is a good choice when you’re sanding soft wood, stripping paint or varnish, or using a high-speed power sander.
Closed-coat paper cuts faster and more smoothly, which makes it the best choice for most other sanding projects. In most cases it makes sense to start with closed-coat paper and switch to an open-coat paper if loading becomes a problem.
One important note: The backing for regular aluminum-oxide sandpaper is not waterproof, which means moisture can ruin the paper. Silicon-carbide paper does have waterproof adhesive and backing, so it’s good for wet or dry applications.
Whenever possible, buy sandpaper by the sleeve (25, 50 or 100 sheets, depending on the grit), because it is much cheaper; the per-sheet price can be half of what you pay for an individual sheet. However, a sleeve of sandpaper can last a long time, so it’s best to store it a moisture-proof box.
To get a uniform finish when hand sanding, back the paper with some type of block, not the irregular tips of your fingers. For flat surfaces use a wooden block; for curved surfaces, use a rubber block or a flexible float. Wrap the paper around the block or attach it with disk adhesive.
If you do need to use your fingers when sanding on a surface—and occasionally you will—put on a good pair of cloth garden gloves, then fold a quarter sheet of paper into thirds. This ensures that the paper will not sand itself and that you get three fresh faces out of each piece.
Always sand with the grain; sanding across the grain introduces scratches that almost certainly will be accentuated by any finish you apply.
Always sand “through the grits.” Begin with a grit that is coarse enough to remove the worst defects, then sand the same surface with progressively finer grit paper until you get the smooth surface you want. In most cases you might start with an 80-grit paper and work up. If you are sanding a wood surface with planer marks, you might begin with a 60-grit paper, or even a 36.
When sanding teak, use 100-grit paper for the exterior woods. For interior work continue up to 120-grit. Other woods might need up to a 220-grit to create a good surface for varnishing.
Never skip a grit size when you are working through the grits. It doesn’t save time and often leaves sandpaper marks.
Sanding sponges are basically grit mounted on a thin sponge backing. They are easy on the fingers, amazingly long-lived and terrific for wet-sanding a bottom before applying a fresh coat of antifouling paint (assuming local regulations allow this). Wet sanding doesn’t create toxic dust, and because a sanding sponge follows the contour of the hull it can cut old paint quickly.
The basic rules for what sandpaper to use, and when, are not complicated. Dry sand with aluminum oxide. Wet sand with silicon carbide. Bottom sand with a sanding sponge.
If only everything else in life were so simple.