Wood Finishing Basics | Popular Woodworking

Understand the basics.

A wooden end is a transparent, clear coating utilized to wooden to guard it from moisture and to make it look richer and deeper. This differs from paint, which is a wooden end loaded with sufficient pigment to cover the wooden. And it differs from a stain, which is a wooden end and a colorant (pigment or dye) with a number of thinner added so the surplus stain is straightforward to wipe off. The the rest simply colours the wooden; it doesn’t cover the wooden.

Unfortunately, the time period “finish” additionally refers back to the complete built-up coating, which might encompass stain, a number of coats of end (a “coat” is one utility layer) and possibly some coloring steps – for instance, glazing or firming – in between these coats. For some cause, we’ve got just one phrase to discuss with each the clear coating used, and to all of the steps used.

Usually, the context makes clear to which is being referred.

Purpose of a Finish

A end serves two functions: safety and ornament.

Protection means resistance to moisture penetration. In all circumstances, the thicker the end, the extra moisture-resistant it’s. Three coats are extra protecting than two, for instance. Boiled linseed oil, 100 p.c tung oil and wax will dry comfortable and gummy, nevertheless, so all the surplus must be wiped off after every utility to realize a purposeful floor. Therefore, no vital thickness may be achieved. Protection is restricted with these finishes.

Finishes beautify by making wooden look richer and deeper. The influence is much less dramatic on unstained lighter woods reminiscent of maple and birch, and higher on stained and darker woods reminiscent of cherry and walnut.

Polyurethanes. The left part of this panel was completed with water-based polyurethane, which, like all water-based finishes, provides little colour to the wooden. The end simply makes the wooden a bit darker (in comparison with the lighter strip down the center, which was coated with tape). The proper part was completed with oil-based polyurethane, which, like most finishes besides water-based finishes, provides some extent of yellow/orange coloring to the wooden. Oil-based polyurethane continues to darken because it ages, whereas water-based polyurethane doesn’t darken.

Types of Wood Finish

Common classes of wooden end embrace the next:

• Oil (boiled linseed oil, 100 p.c tung oil and blends of those oils and polish).
• Oil-based varnish (together with alkyd, polyurethane, spar, wiping and gel varnish).
• Water-based end (a end that thins and cleans up with water).
• Shellac (an historic end derived from resin secretions of the lac bug).
• Lacquer (the end used on virtually all mass-manufactured family furnishings made because the 1920s).
• Numerous two-part, high-performance finishes utilized in business and by {many professional} cupboard outlets.

Wiping varnish is alkyd or polyurethane varnish thinned about half with mineral spirits so it’s simple to wipe on and wipe off. You could make your personal, or there are numerous manufacturers, which, sadly, are poorly labeled. (learn extra on wiping varnish right here)

The major variations within the finishes are as follows:

Finish on oak. On this oak panel, a transparent end was utilized to the left part, paint to the center part and a stain and clear end to the precise part.

■ Scratch, solvent and warmth resistance. Oil-based varnishes and high-performance finishes present the very best scratch, solvent and warmth resistance. Water-based finishes are subsequent. Shellac and lacquer are vulnerable to all three kinds of harm. Oil is just too skinny to be efficient.

■ Color. Water-based finishes add little colour to the wooden. All different finishes (besides probably CAB-Acrylic) add some extent of yellow-to-orange coloring.

■ Drying time. Shellac, lacquer and high-performance finishes dry the quickest. Water-based finishes are subsequent. Varnish and oil require in a single day drying in a heat room.

■ Solvent security. Boiled linseed oil and 100 p.c tung oil are the least poisonous finishes to breathe throughout utility as a result of they don’t include solvent. Water-based finishes (thinned with water and a bit solvent) and shellac (thinned with denatured alcohol) are subsequent. Oil-based varnish thins with mineral spirits (paint thinner), which some individuals discover objectionable however which isn’t particularly poisonous. Lacquer and high-performance finishes skinny with solvents which might be probably the most hazardous to be round.

Sealing Wood

The first coat of any end seals the wooden – that’s, stops up the pores within the wooden so the subsequent coat of end (or different liquids) doesn’t penetrate simply. This first coat raises the grain of the wooden, making it really feel tough. You ought to sand this primary coat (with simply your hand backing the sandpaper) to make it really feel easy. You don’t want a particular product for this primary coat except you could have one in every of two issues you need to overcome.

■ Alkyd varnish and lacquer can gum up sandpaper when sanded, so producers of every present a particular product referred to as “sanding sealer” with dry lubricants added to make sanding simpler and velocity your work. Sanding sealers weaken the end, nevertheless, so it’s best to use them solely while you’re ending a big venture or doing manufacturing work.

■ Sometimes, there are issues within the wooden that should be blocked off with a particular sealer in order that they don’t telegraph by way of all of the coats. These issues are resinous knots in softwoods reminiscent of pine, silicone oil from furnishings polishes that causes the end to bunch up into ridges or hole out into craters, and smoke and animal-urine odors. The end that blocks these issues (“seals them in”) is shellac, and it ought to be used for the primary coat. Notice that, aside from resinous knots, the issues are related to refinishing.

Sheen

Sheen. A end can have an infinite variety of sheens relying on how a lot flatting agent is added.

Oil-based varnishes, water-based finishes and lacquers can be found in a wide range of sheens, starting from gloss to flat. All sheens apart from gloss are created by the solid-particle “flatting agents” producers add to the end. The extra flatting agent added, the flatter the sheen. These flatting particles settle to the underside of the can, so you must stir them into suspension earlier than every use.

You can get any sheen you need by pouring off a number of the gloss from a can wherein the flatting agent has settled (don’t let the shop clerk shake the can) and mixing the 2 elements. Or you possibly can combine cans of gloss and satin to get one thing in between. You might want to apply the end to see the sheen you’ll get. It’s the final coat you apply that determines the sheen (there isn’t any cumulative impact), so you possibly can experiment with every coat.

Finish Application

Oil, wax, wiping varnish and gel varnish may be utilized with a material or brush, then wiped off. The different finishes are normally utilized with a brush or spray gun.

Brushing is easy – primarily no totally different than brushing paint. Spraying can be easy, however spray-gun care and tuning is extra sophisticated, and spray weapons and their sources of air (compressor or turbine) are significantly costlier than brushes.

Application Problems

Common issues and methods to keep away from them:

■ Brush marks and orange peel. Eliminate these by thinning the end 10 p.c to 30 p.c so it ranges higher.

■ Runs and sags. Watch what is occurring in a mirrored mild and brush out the runs and sags as they happen.

■ Dust nibs. Keep your instruments, the end and the air within the room as clear as attainable.

■ Bubbles. Brush again over to pop the bubbles, or skinny the end 10 p.c to 30 p.c so the bubbles have extra time to come out.

No matter what the issue, you possibly can all the time repair it by sanding the end degree and making use of one other coat.