But you may be surprised to learn that the best woodworkers still see a final hand-sanding as an indispensable step to prepare a woodworking project for the final stain and topcoat finish.
Why Hand Sanding Is Necessary
Considering that you can mount a portable power sander with the finest grit sandpapers, you might think that these tools can achieve perfect smoothness. However, virtually all power finish sanders work by moving the pad in some form of orbital or oscillating motion, and this motion has the effect of scraping the abrasives across the grain of the wood—not parallel to the grain, as hand sanding does. Although they may not be seen at first, tiny scratches are the inevitable result of sanding wood with power tools, and these scratches will trap stain and muddy the surface of the wood once the finish coats are applied. By contrast, a fine woodworking piece that receives a good final hand sanding will allow the wood grain to shine through in all its glory.
Types of Sandpaper
There are many types of sandpaper and abrasive materials available, but for finish sanding by hand, the most common choices are:
Aluminum oxide: This sandpaper uses manmade particles as the abrasive material bonded to the flexible paper or fabric backing. Aluminum oxide sandpaper has a familiar brown or yellow-brown color. The abrasives fracture during use, exposing fresh cutting surfaces as work progresses. Aluminum oxide paper is relatively long-lasting when compared to other sandpapers. Most woodworkers keep a good stock of 120-, 150-, 180-, and 220-grit aluminum oxide sandpaper on hand for final sanding of bare wood. For smoothing topcoat finishes between coats, 360- or 400-grit papers are used. Garnet: This is a natural sandpaper, using genuine mineral particles as the abrasives. Garnet sandpaper is typically reddish or reddish-brown in color. It is an effective sandpaper, since the aggregate particles break during use, exposing fresh cutting edges as work progresses. The particles do not adhere particularly well to the backing, however, and garnet sandpapers don’t last as long as aluminum oxide. Garnet sandpaper is, however, less expensive than aluminum oxide sandpaper. Garnet paper is commonly used for sanding bare wood, but it doesn’t work particularly well for sanding between coats of varnish or paint. Silicon carbide: This is another manmade abrasive, this one with a characteristic dark gray or blue-black color. It is often marketed as wet-dry sandpaper, since the backing is a waterproof fabric. Silicon carbide sandpaper is rarely used for sanding bare wood, but it is often used to dry-sand between coats of top finish, and it can be used to wet-sand the final top-coat for a very smooth high-gloss finish. Use 320- or 400-grit paper for this work.
Techniques for Hand Sanding
For today’s woodworker, hand-sanding begins at the point where power sanding has smoothed the project as much as possible. For large smooth surfaces, final hand-sanding may involve one or two passes with 180- and 220-grit paper, aiming mostly at removing the fine scratches left by the power sander. However, woodworking projects with intricate curves may have surfaces that are not adequately smoothed, even by the smallest detail sanders. Here, it may be necessary to sequentially hand sand with 120-, 150-, 180-, and 220-grit sandpaper to achieve complete smoothness. Hand sanding should always be done with a back-and-forth motion that is parallel to the grain of the wood, not across it. Between sanding passes, the surfaces should be wiped clean with a tack cloth or clean cloth moistened with mineral spirits. This will remove sanding dust and keep the wood pores clear so that the subsequent sanding action is effective.
Sanding Blocks
It is best to use sanding blocks when hand sanding, in order to keep the sandpaper in firm contact with the wood surfaces. A flat block will suffice for sanding flat expanses. You can wrap sandpaper around scraps of carpeting, dowels of different sizes, foam pipe insulators, or other makeshift objects to conform the sandpaper to various shapes matching the contours of your woodworking piece. You can also sand by folding the paper and pressing by hand. Try to avoid dulling or rounding over the edges of decorative contours when sanding. When sanding is complete, the wood should feel silky smooth to the touch. Before moving on to staining and top-coating, make sure to wipe the wood clean again.
Sanding Between Finish Coats
Most experienced woodworkers apply two or even three coats of varnish or oil finish to a woodworking project. Between coats, the surfaces should be lightly sanded with 320- or 400-grit silicon carbide sandpaper. Wipe the surfaces clean before applying the next coat. For the very best finishes, some woodworkers take a final step of wet-sanding the final dried topcoat with silicon-carbide wet-dry sandpaper. Use mineral spirits or water as a lubricant, and wipe the surface completely dry after finished. A final buffing with a non-woven synthetic pad will shine the surface to a uniform glossy finish.
Bottom Line
For a truly professional look to your woodworking projects, always hand sand before moving on to staining and finishing. The effort will clearly show in the quality of your finished work.
