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HOW TO


CHOOSING WOOD FINISHES
STAINS, WOOD FINISHES, AND PAINTS are made up of three main components: colorant, binder, and thinner. Stains and paints often contain a colorant, usually a pigment, in a binder that is thinned with solvent or thinner. The key difference is the ratio of colorant to thinner; stain has a greater percentage of thinner, paint has just enough thinner to make it brushable. You want a stain to highlight the grain of the wood, not cover it. Comparatively, you can think of a clear finish as paint without the colorant. Finishes protect the wood, like paint, but they don't color it significantly. Paints containing colorant and binder generally offer the best overall protection.
Finishing is a simple craft that anyone can learn. There are only three tools to choose from: rags, brushes or spray guns, and five common types of finishes
• Oil
• Varnish and Polyurethane
• Shellac
• Lacquer
• Water-based Finish


CHOOSING A CLEAR WOOD FINISH
When you look at all the finishes on paint-store shelves, it's easy to feel overwhelmed by the number of choices. You should look for the following qualities when choosing a finish:
• Protection of the Wood
• Durability
• Ease of Application.

If you want your project to have a long life, choose a finish that offers maximum resistance to moisture vapor exchange. Within each finish type, the thicker the finish, the better it slows down this exchange.
Be careful, too much can be as bad as too little. Film thicknesses greater than about .006 inchabout 4 or 5 coats of polyurethane-have a tendency to crack, especially if the weather goes through sudden changes.

Durability
Durability is the degree to which a film finish itself resists damage. Some finishes are more resistant to scratches, water, and heat than others. Finish durability is not all that important, for a decorative object that will sit on a fireplace mantle. But for a table top or set of kitchen cabinets, finish durability is very important. In these cases, the finish will probably be subjected to a great deal of abuse. Thicker films are more durable, but thickness is not as important as the type of finish. For example, polyurethanes are much more durable than waterbased finishes.

Ease of Application
Assuming you have access to all three finish application tools�rags, brushes, and a spray gun � the quality that is most important for making finishes easy to apply is drying time. This may surprise you until you recall the problems you have had in the past with dust settling on slow-drying finishes, like polyurethanes.
The problem with a fast drying finish is that it is very difficult to apply without a spray gun. If you don't have spray equipment, you'll have to choose slower drying finishes and deal with the dust. Oil finishes are an exception to the rule. With oils, you wipe off the excess finish after each coat. Fast drying isn't important since there isn't enough finish left on the surface for the dust to stick to.

TYPES OF WOOD FINISHES
There are many types of finishes, but only a few are used for wood. It's more helpful to concentrate on types than on brands, since the brand differences within each type are small.
Oil finishes are the easiest to differentiate because they don't cure hard, and as a result, cannot be built up into a hard film finish. Varnish, shellac, lacquer and water-based finishes do cure hard and can be built up as you add coats. Oil finishes are generally easier to apply than film finishes, while film finishes offer more protection.

Oil
There are two types of oils: those that cure, and those that don't. Oils that cure can be used as finishes since they seal the wood and can produce a fairly permanent sheen. Oils that don't cure don't perform well because they continue to sink deeper in the wood leaving the surface unprotected, or they remain sticky on the surface. There are two common oils that cure and perform well as finishes: linseed oil and tung oil.

Linseed Oil. Pressed from the seed of the flax plant, in its raw form, linseed oil takes a week or longer to cure. Some manufacturers add metallic driers which make the oil cure in about a day. Linseed oil with added driers is referred to as "boiled."

Tung Oil. Pressed from the nuts of the tung tree, pure tung oil does not have driers added and requires several days to cure.
Neither oil is particularly protective or durable. The main reason for their popularity is that oils are easy to apply.

Applying oil wood finishes
All that is required to apply an oil finish is to wipe or brush the oil onto the wood, let the oil soak in for five to ten minutes during which time you should rewet any places that dry out, and then wipe off all the excess. Allow the boiled linseed oil to cure overnight; tung oil requires about three days. Sand the surface lightly before applying a second coat. Two to three coats of boiled linseed oil will produce an attractive "rubbed" sheen. Tung oil may require as many as five or six coats to build an equivalent looking finish. Tung oil also tends to cure rough for the first several coats. Continue to sand lightly between coats until the top coats cure smoothly.

Repairing and restoring oil finishes
Though oil finishes are not very protective, they are by far the easiest to repair in the event that they become scratched or dull. Simply wipe on another coat of oil (you can mix oils without any ill effects), and wipe off the excess.

Varnish
Varnishes are produced by cooking an oil, with a resin. The resins used today are synthetic alkyds, phenolics, and polyurethanes. In fact, "polyurethane" is technically a varnish made with polyurethane resins. The polyurethane resins make this type of varnish a little more protective and durable than other types of varnish.
When more oil and less resin is used in the manufacture, the resulting varnish is softer and more flexible. This type of varnish, called "spar" varnish, is best for outdoor use because it flexes better with outdoor wood movement.
Varnish is one of the most protective and durable of all finishes. In addition, three or four coats offers more protection than one or two. The downside is that varnish is slow drying. As dust settles and sticks to the surface, it will ruin the finish.

Applying varnish
Varnish is usually applied with a brush, just like paint. The only major difference is that cleanliness and the right technique are more important because dust and paint strokes are clearer in a finish than they are in paint.
Make an extra effort to make your work room as dust-free as possible. Dust all surfaces and damp mop the work area before beginning. To remove dust from the wood, use a tack cloth. Use a clean brush to transfer the varnish to a separate container. Strain out the particles in the varnish, using a paint strainer or cheese cloth.
Begin spreading the varnish onto the wood in any direction. As you move from section to section, tip off the varnish in the direction of the wood grain. To tip off, hold the brush almost vertical, and use a light touch. Line up the brush strokes with the wood grain so that they are less noticeable. On horizontal surfaces begin at the far edge and brush from left to right. Brush your body so that dust doesn't fall off your arm onto the already applied varnish.
To remove runs and sags, drag your brush over a clean jar edge to remove any excess varnish. Then lightly rebrush the problem area.
There is no way to totally eliminate dust settling on your fresh varnish finish. If the dust nibs are very noticeable, you can sand them out. Sand between coats with 220- or finer-grit paper. After the last coat, follow up with 600-grit wet-or-dry sandpaper. With this paper, you can use water or mineral oil as a lubricant. Rub the surface with #0000 steel wool to produce an even sheen.

Wiping Varnish
When varnish is thinned about half with paint thinner it is easy to wipe on the wood, and so it's called "wiping varnish." (Many manufacturers refer to their
wiping varnishes as "tung oil"-read the label carefully.) Realize that a wiping varnish is entirely different from tung oil finishes. Varnish, whether thinned or full-strength, cures to a hard, smooth film. Tung oil takes months to cure, and cures to a soft and wrinkled film.
Because of the confused naming, you may need to test your finish in order to determine what you're working with. To test, pour some finish onto a nonporous surface like glass or plastic laminate and allow it to dry. If the puddle cures hard and smooth, the product is a varnish. If the puddle cures soft and wrinkled, or doesn't cure at all, then it is tung oil, or some oil/varnish blend.
You can apply wiping varnish just like full strength varnish by brushing it on the wood and leaving it to cure. Or you can apply it like an oil finish and wipe it onto the wood, and then wipe off any excess. You can also leave a little of the varnish on the wood to achieve a thicker build-up for more protection. This is not possible with an oil finish.

OiI/Varnish Blend
Varnish can also be mixed with linseed or tung oil in any proportion. When this is done, the product is little more protective and durable than oil alone, but still cures to a soft, wrinkled film. Wipe off all the excess finish after each coat.
Apply oil/varnish-blend finishes just like boiled linseed oil. Let the first coat soak in for five to ten minutes, then wipe off any excess. Steel wool the surface the next day, then apply a second coat.
SHELLAC
Shellac is the only natural resin still widely used to make a finish. Although shellac may not be as water-resistant as varnish or lacquer, it is quite resistant. (For tabletops and kitchen cabinets, you should consider a more durable finish.) Imperfect drying occurs when the shellac has begun to deteriorate in the can. Shellac breaks down slowly, but over a period of a year or two you can tell that the shellac takes longer to dry and never gets as hard. For that reason, you should always buy the freshest shellac you can find. Most cans are stamped with the date of manufacture. Try to find a can that is no more than six months to a year old. Shellac varies in color between orange (amber) and clear. Orange shellac adds warmth to woods like walnut, pine, maple and oak. Clear shellac is best if you don't want to add color to the wood.
Shellac's fast drying property is a real advantage for reducing dust problems. Shellac dries quickly as its alcohol solvent evaporates. In most cases, this is fast enough so that dust doesn't have time to settle. The disadvantage to a fast-drying finish is that it is a little difficult to apply with a brush.

Applying Shellac
Shellac is difficult to brush straight out of the can. It's too thick, doesn't flow out well, and dries too quickly. Thin the shellac about 50/50 with denatured alcohol. The more you thin shellac the easier it is to brush out, but the thinner each coat becomes. Because shellac dries faster than varnish, you will have to follow a new brushing procedure. Begin brushing close to the way you want the brush strokes to line up. You won't have as much time to come back and line them up as you do with varnish. The trick is to move fast enough so that each new brush stroke overlaps the second that is still wet. If the previous stroke has begun to set up, your brush will drag, creating little ridges that will cure in the finish. To get ridges out, allow the finish to cure, sand the surface, then apply a second coat.

LACQUER
Lacquer is the primary finish used in factories and professional finishers and refinishers. This is because the lacquer dries very fast, reducing dust problems, and is easy to apply with a spray gun. The downside is that solvent fumes left by spraying lacquer are bad for your health. The residual dry lacquer dust can also be explosive. As a result, few homeowners use lacquer.
There are lacquers that cure slowly enough so that they can be brushed. Employ strong-smelling solvents, these "brushing lacquers" are no more difficult to apply than shellac.
Though it is more expensive, you can purchase lacquer in aerosol spray cans. You might find this convenient for finishing small projects.

WATER-BASED WOOD FINISHES
Due in part to stricter air-quality laws, a new market has been created for water-based finishes. These finishes are often marketed as "varnish," "polyurethane," and "lacquer," which confuses them with their solvent-based competition. Water-based finishes, however, are always identifiable by some mention of water clean-up on the can. Water-based finishes are essentially latex paint without the pigment. Like latex, water-based finishes are easy to clean up and don't smell that bad. Its limitations are pronounced brush markings and reduced durability. Compared to oil-based varnish, water-based finishes are much less resistant to heat, solvent, acid, and alkali damage. In addition, water based finishes tend to bubble.

Applying Water-Based Wood Finishes
Weather conditions are critical to achieving good results. Work in conditions as close as possible to 70 degrees Fahrenheit and 40 percent humidity. Use a synthetic bristle brush and don't overbrush the surface, otherwise you'll just make more bubbles. Lay down a level coat in as few passes as possible. Keep in mind that bubbles pop out of thin coats easier than thick coats. Try to brush only in the direction of the wood grain because you won't have much time to tip off your brush strokes after they've been applied. Apply each brush stroke rapidly enough so that the previous stroke is still wet when you overlap it.

FINISHING THE WOOD FINISH
All finishes can be improved in appearance and feel by rubbing them with an abrasive after they have cured. It is wise to practice this step on a scrap before doing it on a project because you don't want to cut through the finish.
The easiest way to rub a finish is with #0000 steel wool, or a synthetic abrasive pad. Rub in long strokes following the direction of the wood grain. Avoid making arcs with your strokes.



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Updated: 09/2017   copyright 2012 U-Repair.com