As a raw material for cabinets and furniture, plywood has a lot going for it. It’s constructed in layers, that makes it resistant to warping, and it comes in 4-by-8-foot sheets, letting you make broad tabletops and cabinet faces without having to laminate boards. Since plywood has a veneered surface, it is harmful to oversand this, and you must do something about the advantages. Apart from that, it is as easy to finish as wood.
Whether you are using plywood having a center made of fiberboard or softwood, the layers are visible to the borders. A frequent strategy is to cut strips from timber which matches the plywood facing and glue or nail them. An even simpler approach is to cover them with vinyl or metal beading. Should you choose to prevent the excess function that installing beading entails, however, you can round the edges with sandpaper. You’ll likely find voids — small gaps in the plywood layers — which need filling, and when there are a huge number, the filler may may be apparent. In cases like this, try painting the borders after sanding and filling using a color that blends with the face veneer.
When sanding plywood, it is important to treat the surface as the veneered layer it is and prevent bearing down with a orbital sander, or you may mud straight through it. This is especially easy to do when sanding borders. Use the machine to smooth the grain, then quit using it and complete the sanding by hand, going with the grain using 120- or even 150-grit sandpaper. This is also the best method to remove the swirl marks left by the orbital sander, which may only appear when you apply the finish. To avoid surprises, then check for them with a rag dampened with mineral spirits before you stain and complete.
Overcoming the Blotches
Plywood comes with a variety of wood facings, and a number of them have a grain which accepts stain unevenly — a few examples are birch, fir and pine. You should treat those with wood conditioner before applying a pigment-based stain. The conditioner is similar to a very dilute end — it soaks to the seals and grain it so the stain spreads out evenly without blotching. An alternative is to use a thin coat of shellac. Shellac is a surface layer, and it wo not penetrate deeply enough to cause blotching or other hurdles.
Painting and Finishing
Just as you should precede a crystal clear finish using a sealer, you need to prime plywood before painting it. If your job involves knotty plywood, use a solvent-based, stain-blocking primer to stop tannins in the knots from bleeding through the paint. Water-based primers and sealers raise the grain of the surface layer, and that’s easy to knock down by using a light hand sanding, using 220- or even 300-grit sandpaper. You’ll probably need two or more coats of paint or complete, and you’ll get the smoothest surface by sanding every coat lightly after it dries and before you apply the next one.