Tips and tricks can turn out a better finish - Woodshop News

Tips and tricks can turn out a better finish

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The following are some random tips to speed and improve your finishing. They are arranged roughly in the order of the steps.

Soften sharp edges

Machining wood leaves edges sharp. Always soften them with several light passes of medium-grit sandpaper before applying a finish. Film-building finishes will peel away from sharp edges if they aren’t rounded over a little and sharp edges damage easier than softened edges.

Applying stain

The most efficient methods of applying stain are by wiping or spraying. Brushing is very slow — often too slow with lacquer and water-based stains that dry rapidly.

When you have thoroughly wetted a surface with the stain, quickly wipe off the excess. With fast-drying stains, try dividing large projects into smaller sections to give yourself enough time or get someone else to apply or wipe off.

Bury raised grain

Water-based stains and finishes raise wood fibers and lock them in place, making the surface feel rough. You can pre-raise the grain by wetting the wood and sanding it smooth after it has dried. But it’s much more efficient to “bury” the raised grain with another coat of finish. Then sand it smooth after it has dried.

Color confirmation

Stains lighten as they dry, then return to their damp color when a finish is applied. So the quick method of seeing the color you’ll get with the finish applied is to look at the stain while it is still damp.

If you’re using a satin or flat finish, however, you need to factor in the impact of the flatting agent. It will dull the brightness of the color a little.

Avoiding runs and sags

You should never have runs or sags in your dried finish. The way to achieve this level of perfection is to watch the surface you’re brushing or spraying in a reflected light. You might need to arrange some lights or move your body and your head often to see what’s happening.

With a reflection, you can see easily when a finish begins sagging or running. Then it’s a simple matter of using a brush (even if you’re spraying) to remove the problem. Lift the excess finish off the surface with the brush and spread it to another part, drag it over the lip of a jar or can or wipe it on a clean cloth.

Best bar-top finish

The best finish to use for bar tops, restaurant tables or kitchen tables depends largely on how you intend to apply it.

For a pour-on finish, epoxy resin is best. Just like epoxy adhesive, it comes in two parts, which you mix before pouring onto the surface and spreading evenly using a plastic spreader.

If you’re using a spray gun, the best finish is catalyzed (“conversion”) varnish, which also comes in two parts for you to mix before spraying. Close behind in durability are one- and two-part catalyzed lacquers.

If you’re brushing the finish, oil-based polyurethane is best. It is significantly more durable than water-based polyurethane because alcohol spills and the chemicals used for cleaning will soften water-based polyurethane over time.

Avoid rough surfaces in confined spaces

When spraying in enclosed areas, such as the insides of cabinets or drawers, with a fast-drying finish, it’s common to get a rough-feeling finish. The bounce-back and turbulence created by the force of the spray — even HVLP spray — keeps the finish particles in the air long enough to dry. Then they settle and stick to the surface.

To prevent this from happening, slow the drying of the finish with a retarder. In some situations, you can remove the back of the cabinet or the drawer bottom so the bounce-back can be exhausted.

Lacquer over stain or glaze

As long as you are using a spray gun for application and solvent lacquer for your finish, you don’t have to let an oil-based stain or glaze dry overnight before applying the finish.

The trick is to mist (or “dust”) some lacquer onto the stain or glaze after the thinner has evaporated (the stain or glaze dulls) but before the oil binder begins oxidizing and becomes tacky. Unless the stain or glaze is thick, in which case this trick might not work, the lacquer incorporates the uncured stain or glaze and bonds to the wood or finish coat underneath.

After the mist coat dries, continue with your finish coats. It would be a good idea to practice on scrap wood first to be sure you have the timing right. If the timing is wrong, the finish could wrinkle or turn white.

Matching colors

Matching colors is one of the most difficult tasks in wood finishing. It’s rare that a stain alone accomplishes a match. The best procedure is to get the color close, but a little on the light side with a stain. Then tweak the color by applying a glaze or spraying a toner.

To get a preview of what the glaze or toner will do, apply some to a clean glass plate and place it on the stained wood to which you have applied a coat of finish to show the true color. You’ll know right away if you have a match or what you need to do to get closer.

Removing dust nibs

There’s almost always a little dust that settles onto the last coat of finish before it dries, even with fast-drying lacquer. As long as the dust isn’t excessive or the particles large, you can make the surface feel smooth by rubbing with a folded brown paper bag after the finish has fully dried.

Smoothness is important because people like to touch the finish. Smoothness says quality.

Use a plastic spreader when rubbing a finish

When leveling a finish with sandpaper and a lubricant, you can get a quick view of where you are in the process by using a plastic spreader to remove the sludge from an area. As long as the finish you applied has a gloss sheen, dips and pores where you haven’t sanded enough show up well.

The plastic-spreader trick is a lot quicker than washing off all the sludge with a rag and solvent — or a rag and water — and you don’t have to let the solvent or water dry to see what’s happening. The shiny areas show up immediately.

Rough up surface before stripping

High-performance coatings are often difficult to strip because they are designed to resist damage from solvents. To give your solvent stripper a better chance of working, rough up the surface with coarse sandpaper first. This radically increases the surface area for the stripping solvent to attack.

Then give the stripper a longer time to work, if necessary, by keeping it wet on the surface.

Bob Flexner is author of “Understanding Wood Finishing” and “Flexner on Finishing.”

This article originally appeared in the May 2015 issue.

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