Preparing Wood for Stain or Varnish

This story covers the procedures and tools available to prepare wood for painting.

Preparing Wood

Make the wood as smooth and perfect as possible to ensure a great finish. Find and fill defects, conceal unsightly edges in plywood, and sand thoroughly.

Detecting defects
Natural defects in wood include tiny, solid knots; thin splits or cracks; and minuscule pest holes. Inspect your wood carefully for these and note them. If you find them on hardwood that will be stained and clear finished, wait until after you've completed the finishing to take care of them. Then apply a putty that matches the final finish. If you repair blemishes before staining and finishing, the repair will finish differently than the wood and will be more obvious.

One way to fill small gaps and minor imperfections before applying the clear finish is to mix some of the wood's own sawdust with a bit of the finish and fill with that. Fine dust from sanding is best; the dust-collecting bag or cup of a finishing sander is a great source. You can also purchase a commercially prepared stainable filler in a matching color.

Use a commercial filler or exterior patching compound to smooth the rough edges of softwood plywood you plan to paint. Then sand the repair. For hardwood plywood, use iron-on veneer tape of the same wood species. In some cases moldings can both conceal the edge and add style.

Sand smooth
Do all final sanding with orange-color, open-coat garnet sandpaper. Dust won't clog it as easily as closed-coat papers, and the garnet particles fracture as you use them, producing an increasingly finer grit. For hand-sanding, "A" weight paper works best. Wrap it around a sanding block so the surface you're working on remains flat as you smooth it.

The higher the grit number, the finer the grit. For most work, start with 100-grit, then use 150-grit, and end with 220-grit. Clean the surface of the wood between sandings with a vacuum, a tack cloth, or a paper towel lightly dampened with a solvent such as mineral spirits.

Filling Nail Holes

Use a nail set and a hammer to drive the head of finishing nails below the surface. Press wood filler into the hole, let it dry, then sand flush.

Covering Blemishes

Softwood and softwood plywood often have blemishes that will show through a finish. To prevent this, apply wood filler with a putty knife, then sand when dry.

Edges: Wood Filler

Softwood plywood edges usually look rough. Before painting plywood edges, spread wood filler in the voids and sand smooth when dry. Exterior patching compound also works well.

Edges: Veneer Tape

Easily applied, heat-activated veneer tape neatly covers hardwood plywood edges. Simply trim it with a utility knife, and use an iron set on medium-low heat to adhere the tape.

Sanding: Belt Sander

A belt sander quickly smooths large surfaces, such as plywood sheets. It is aggressive, however, so keep it moving. If held too long in one place, it can dig into the wood and cause a low spot.

Sanding: Orbital Finishing Sander

Orbital finishing sanders do a fine job on hardwoods. They are lightweight and maneuverable and are handy for small areas and narrow parts. With a random-orbit sander, you can sand in all directions across the grain and not leave swirl marks.

Sanding: Sanding Block

A sanding block produces the best results when hand-sanding. Purchase one or make one from a piece of scrap wood. Change paper frequently.

Comments (5)
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