Not many people enjoy sanding. Even with powered equipment it can be hard, repetitive work. But it’s very important to have a smooth level surface on your projects. Not only does it look better when you apply the finish, it feels better to the touch. Everyone knows that you start with a low grit and work your way up. But the starting grit you choose makes a big difference. Here’s a little secret; the lowest grit paper you pick to start sanding with is the one that does all the work of smoothing the surface. After that you’re just removing scratches from the last grit until eventually the scratches are too small to notice. It really helps to know about sandpaper and think about where to begin and end.
Curiously, the sandpaper you’re using doesn’t contain sand and may not even contain paper. The abrasive grains are made from a variety of minerals depending on the materials to be sanded. The ones most commonly used for woodworking are:
- Garnet —used in woodworking or to polish metal
- Aluminium Oxide — the most common abrasive. Used on wood or metal.
- Silicon Carbide — common in wet applications, available from coarse grits to microgrits
The mineral’s sharp edges are effectively cutting tools that remove material as they pass over it. The size of the grains determines how aggressively they cut and the space between the grains provides a place for the cut material to go, much like the kerf in a saw blade. Common sandpaper grits range from 36 to 5000 or more.
The backing or ‘paper’ can be anything from paper, to cloth, film, or rubber. A flexible backing allows sandpaper to follow irregular contours of a workpiece while a stiff holds up better. Generally speaking, the harder the backing material, the faster the sanding, the faster the wear of the paper and the rougher the sanded surface. Chose the right paper and always work your way up through each available grit level to be sure you are removing all the scratches from the previous level.
When you start sanding, first consider how low you need to go. You’ll save a lot of work if you can avoid using extra grits. The starting grit depends on how rough the surface is and how hard the material is that you are sanding. Instead of reaching for the 40 grit sandpaper, see if you can start at 100 or 120 grit. Worst case, you may need to drop down a few levels if it’s going too slowly. On wood, you’ll likely want to stop at 180 or 200 grit. You’ll still get a nice finish and if you polish the surface with grits above 220, it may be too smooth to absorb stain.
The first recorded use of sandpaper was in 1st-century China when crushed shells, seeds, and sand were bonded to parchment using natural gum. Sanding is still hard work but today’s modern materials make it a lot easier and more effective.