Wood Finishing 101, Revised Edition

Understanding Stains

Stains & Staining

DEFINITION

A stain is a colorant (pigment or dye) and a binder (some sort of finish) with a lot of thinner added so the excess stain is easy to wipe off. This leaves some color in or on the wood.

A stain can also be just dye and thinner with no binder added.

PIGMENT

Pigment is ground earth or colored synthetic particles, so pigment requires a binder to glue it to the wood. Pigment settles to the bottom of the can and has to be stirred into suspension before use.

DYE

Dye is a colorant dissolved in a liquid, so dye penetrates well and doesn’t need a binder. Coffee and tea are examples of weak dyes.

Pigment settles to the bottom of the can and has to be stirred.

PURPOSE OF A STAIN

There are three good reasons to use a stain:

1. To make a cheaper, less interesting (usually lighter) wood look like a more expensive (usually darker) wood such as walnut, cherry or mahogany.

2. To match the color of an existing object.

3. To create a décor you or someone else has in mind.

TYPES OF STAIN

Common categories of wood stain include:

•Oil stain (thins and cleans up with mineral spirits).

•Water-based stain (thins and cleans up with water).

One of the principal reasons to stain wood, especially lighter woods, is to make them resemble more desirable darker woods, in this case walnut (on the right).

There are five common types of stain. From left to right are examples of oil stain, water-based stain, gel stain, two types of dye stain (concentrated and thinned liquid, and powder), and combination stain and varnish.

•Gel stain (thick in the can like mayonnaise but spreads and wipes off easily).

•Dye stain (a colorant dissolved in a liquid).

•Combination stain and finish (doesn’t color effectively if wiped off and is streaky with brush marks if brushed and left thick).

The primary differences in stains are as follows:

•Ease of application. Oil stains are the easiest to apply because you have plenty of time to wipe off the excess. All the other stains dry quickly so you have to work fast or on smaller areas at a time.

•Drying time. Dye stains dissolved in solvent (not water), can be coated over within minutes. Water-based stains can be coated over after about an hour. Gel stains, and dyes dissolved in water, require 4 to 6 hours before coating over. Oil stains should be allowed overnight drying.

•Grain definition. All stains provide good grain definition if the excess is wiped off, because more colorant is left in the grain. Dye stains produce slightly less definition than pigment stains.

•Color control. Dye stains provide the best control of color — that is, getting the color darker without obscuring the figure of the wood. Dye is see-through; you can apply as many coats as you want and still see the wood’s figure. Pigment hides the wood’s figure if built up.

The basic rule for applying all stains is to apply a wet coat and wipe off the excess before it dries. It’s much faster to apply stain with a cloth than a brush.

STAIN APPLICATION

The basic rule for applying all stains is to apply a wet coat and wipe off the excess before the stain dries. Unless the wood is naturally blotch-prone or you haven’t sanded the wood well enough to remove all gouges and scratches, you will always get an even coloring.

You may need to divide your project into smaller sections, or have a second person wipe as you apply, to get good results using one of the faster drying stains. It’s much faster to wipe the stain onto the wood with a cloth, wearing gloves of course, than to brush it. (I can’t remember ever brushing a stain.)

A washcoat, which is any finish thinned to about 10% solids, can be used to reduce blotching, but it also reduces the intensity of the stain’s color. On this sample, I applied a varnish washcoat (wood conditioner) to the left side of the pine panel and let it dry overnight. Then I applied a stain to the entire panel.

APPLICATION PROBLEMS

Common problems and ways to avoid them:

•The stain dries in spots before you get it all wiped off, leaving an uneven coloring. If you are quick enough, you can wipe more stain on smaller sections at a time to reliquify the stain so you can then wipe it off evenly. Otherwise, strip with lacquer thinner, acetone or paint stripper and restain smaller parts at a time (or get a second person to help).

•The color of the stain doesn’t match what you expected from the name on the label. Names are simply manufacturer’s interpretations. There are no industry standards. One manufacturer’s mahogany may differ from another manufacturer’s mahogany, for example.

•The color of the stain on your project isn’t the same as on the color sample in the store. Woods color differently. Always try the stain on scrap from your project, sanded to the same grit sandpaper, and make adjustments (add pigment, thinner or mix with another color stain) if necessary to get what you want.

•Glue from squeeze-out or fingerprints seals the wood preventing stain penetration. Sand or scrape off the glue through the stain and restain that area, or leave the splotch and disguise it by painting in the correct coloring after you have applied a coat of finish.

Stain problems such as blotching and getting the color wrong can be extremely difficult to fix. You can usually remove some of the color by wiping with the thinner for the stain. If the stain contains a binder (it isn’t simply dye), you can use a paint stripper. But nothing short of sanding will remove all the color.

CONDITIONING THE WOOD

The purpose of conditioning or washcoating wood before applying a stain is to reduce blotching, which is uneven coloring caused by varying densities in the wood. A wood conditioner (also called stain controller) or washcoat is any finish thinned to about 10% solids so it doesn’t fully seal the wood. Some of the stain can still penetrate.

The woods that blotch are softwoods such as pine, and tight-grain hardwoods such as maple, birch and cherry. There’s no point in applying a wood conditioner/washcoat to medium- or coarse-grain woods such as walnut, mahogany or oak.

Varnish wood conditioners (the common ones found in home centers and paint stores) are varnish thinned with about two parts mineral spirits (paint thinner). You can make your own. The key to getting the wood conditioner to work is to let it dry fully before applying the stain — at least 6 hours, better overnight.

Understanding Finishes

Finishes & Finishing

DEFINITION

A wood finish is a clear, transparent coating applied to wood to protect it from moisture and to make it look richer and deeper. This differs from paint, which is a wood finish loaded with enough pigment to hide the wood. And it differs from a stain, which is a wood finish and a colorant (pigment or dye) with a lot of thinner added so the excess stain is easy to wipe off. The remainder just colors the wood; it doesn’t hide the wood.

A stain can also be a thinned dye with no wood finish added.

ANOTHER DEFINITION

The term finish can also refer to the entire built-up coating, which could consist of stain, several coats of finish (a coat is one application layer) and maybe some coloring steps in between these coats. For some reason, we have only one word to refer both to the clear coating used, and to all the steps used.

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

PURPOSE OF A FINISH

A finish serves two purposes: protection and decoration.

Protection means resistance to moisture penetration. In all cases, the thicker the finish the more moisture resistant it is. Three coats are more protective than two, for example. Boiled linseed oil, 100% tung oil and wax dry soft and gummy, so all the excess has to be wiped off after each application to achieve a functional surface. Therefore, no significant thickness or protection can be achieved.

Finishes decorate wood by making it look richer and deeper. The impact is less on unstained lighter woods such as maple and birch, and greater on stained and darker woods such as cherry and walnut.

TYPES OF WOOD FINISHES

•Oil (boiled linseed oil, 100% tung oil and blends of these oils and varnish).

•Oil-based varnish (including alkyd, polyurethane, spar, wiping and gel varnish).

•Water-based finish (a finish that thins and cleans up with water).

•Shellac (an ancient finish derived from resin secretions of the lac bug).

•Lacquer (the finish used on almost all household furniture made since the 1920s) and

•A large number of two-part, high-performance finishes used in industry and by many professional cabinet shops.

PRIMARY DIFFERENCES AMONG THE TYPES

Scratch, solvent and heat resistance.

•Oil-based varnishes and high-performance finishes provide the best scratch, solvent and heat resistance.

•Water-based finishes are next.

•Shellac and lacquer are susceptible to all three types of damage.

•Oil is too thin to be effective.

Color.

•Water-based finishes add no color to the wood and don’t darken as they age.

•All the other finishes add some degree of yellow-to-orange coloring and continue to darken a little as they age.

Three types of coatings: Top; just clear finish, middle; paint, bottom; stain. The bands separating the sections are left uncoated, for comparison.

The left section of this panel was finished with acrylic water-based polyurethane, which, like all these finishes, adds no color to the wood. The finish just makes the wood a little darker (compared to the lighter strip down the middle, which was covered with tape). The right section was finished with oil-based polyurethane, which, like all finishes except water-based finishes, adds some degree of yellow/orange coloring to the wood. Oil-based polyurethane continues to darken as it ages, while water-based polyurethane doesn’t darken anymore.

Drying time.

•Shellac, lacquer and high-performance finishes dry the fastest.

•Water-based finishes are next.

•Varnish and oil require overnight drying in a warm room.

Solvent safety.

•Boiled linseed oil and 100% tung oil are the least toxic finishes to breathe during application because they don’t contain solvent.

•Water-based finishes (thinned with water and a little solvent) and shellac (thinned with denatured alcohol) are next.

•Oil-based varnish thins with mineral spirits (paint thinner), which some people find objectionable but which isn’t especially toxic.

•Lacquer and high-performance finishes thin with solvents that are the most toxic to be around.

SEALING WOOD

The first coat of any finish seals the wood — that is, stops up the pores in the wood so the next coat of finish (or other liquids) don’t penetrate easily. This first coat raises the grain of the wood making it feel rough. You should sand this first coat (with just your hand backing the sandpaper) to make it feel smooth. You don’t need a special product for this first coat unless you have one of two problems you want to overcome.

•Alkyd varnish and lacquer gum up sandpaper when sanded, so manufacturers of each provide a special product called sanding sealer with dry lubricants added to make sanding easier and speed your work. Sanding sealers weaken the finish, however, so you should use them only when you’re finishing a large project or doing production work.

•Sometimes, there are problems in the wood that have to be blocked off with a special sealer so they don’t telegraph through all the coats. These problems are resinous knots in softwoods such as pine, silicone oil from furniture polishes that causes the finish to bunch up into ridges or hollow out into craters, and smoke and animal-urine odors. The finish that blocks these problems (seals them in) is shellac and should be used for the first coat. Notice that, except for resinous knots, the problems occur only in refinishing.

A finish can have an infinite