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This section answers some of the most common questions people ask about finishing. If you don't see your question here, try looking it up in the Dictionary of Finishing Terms, or check the introductions of the preceding chapters.
Most Common Finishing Mistakes
1) Not testing the finish on scrap FIRST.
Solution: ALWAYS test the stain and the topcoat over the satin before committing your whole project.
2) Inadequate preparation before finishing.
Solution: Sand thoroughly, never skip grits. Light pencil marks may help indicate when an area has been sanded sufficiently with a particular grit.
3) Failure to seal wood when necessary.
Solution: Always seal refinished pieces with dewaxed shellac, as they tend to contain silicone oil or waxes. Seal woods like cherry and pine before staining to prevent blotching. Seal aniline dyes in with dewaxed shellac before applying a waterborne topcoat. Seal end grain with wood size or shellac to prevent too much stain from being absorbed.
Babysafe and Foodsafe Finishes
Question: What finishes are safe for use on baby furniture or food utensils?
Almost all finishes made today are nontoxic when cured, however some oil finishes may contain Japan driers, which may contain heavy metals. Finishes labeled as safe for toys or food utensils are naturally safe for such applications. In addition, shellac, natural waxes, and pure linseed or tung oil are safe when cured.
Bar Top Finish
Question: What is the thick, clear finish used on bar tops?
There are finishes specially formulated to be applied by pouring them on in a thick coat. Epoxy comes as a two-part solution that is mixed and poured, then the epoxy (hopefully!) removes the bubbles formed by the mixing process on its own. Acrylic resin is also used as a bar top finish. As a rule, bar top finishes are expensive and it is difficult to get good results without practice.
Question: How do I bleach wood?
Wood can be bleached using a two-part wood bleach kit. The kit contains concentrated solutions of lye and peroxide. Household bleach is not strong enough to bleach wood unless it is left on the wood for a very, very long time. Follow the manufacturer's directions for the wood bleach and neutralize it as directed. For a less extreme bleaching effect, only leave the lye to work for 30 seconds, and repeat the bleaching process as necessary until the desired effect is reached.
Brush Care and Cleaning
Question: How do I care for my good brushes?
Brush care is simple: before use, dip the brush up to the ferrule (metal
band) in the solvent for whatever finish you're using, then shake the brush
(not too violently) to remove most of the solvent. Then dip no more than
1/3 the length of the bristles into the finish and begin finishing your project.
As you continue finishing, dip the brush in the solvent every 10 to 15 minutes
and shake again. This keeps finish from forming a crust high on the
After you have finished working with the brush, gently squeeze any excess finish from the bristles and soak it in solvent for a few minutes. The best way to soak brushes is in a tall jar or can, with the brush suspended so its bristles do not touch the bottom. A plastic lid with just a slit in it works well for this. Poke the brush handle through the slit; friction will hold it where you leave it. After soaking a minute or two, massage the brush bristles to clean out all the finish. It may take a few changes of solvent to clean the brush. Once the brush has been cleaned in whatever solvent you're using, wash it in warm, soapy water and spin it dry. This is accomplished by holding the handle between your palms and making the motion of vigorously rubbing your palms together. Finally, roll the brush in a paper towel or its original wrapper to keep the bristles neatly shaped as they dry.
Question: What brush is best for my finish?
There are three basic types of brush: disposable foam brushes, synthetic
bristle brushes, and natural bristle brushes. Foam brushes require no cleanup,
but may cause foaming in some finishes, and are dissolved by lacquers. Synthetic
bristle brushes work well with waterborne coatings such as latex paint and
waterborne polyurethane. Paint applicator pads also work well, especially
with waterborne acrylics. Natural bristle brushes work best on oil base
varnishes, lacquer, and shellac. Natural bristles do not work well on waterborne
coatings because the bristles absorb the water, become soft, and splay out
in all directions.
Bristle shape is also a factor in choosing the best brush for the job. Brushes may come with tipped, tapered, or flagged bristles. Tipped or square cut bristles are synthetic or natural bristles that have simply been trimmed to length. The blunt ends work well for spreading thick latexes. Tapered bristles are thicker near the handle and become thinner near the tip of the brush. These are found in natural bristles and synthetic Taklon brushes. The taper makes the bristle springier. Flagged bristles have "split ends", a feature that allows them to hold more finish and leave less prominent brush marks. Tapered and flagged bristles are preferred for wood finishing. Flagged bristles are also used for dusting brushes.
Finally, the shape of the brush affects its use. A flat cut brush has bristles cut square across the end, and usually features tipped bristles. It is used for heavy exterior paints. A chisel cut brush has bristles that are shaped to a more rounded profile from front to back across the brush. Chisel cut brushes are the type most commonly used for wood finishing and some interior painting. Oval chisel cut brushes are chisel cut brushes that are thicker at the center than at the edges. These are good for shellac and lacquers because the oval shape allows the brush to hold more finish, reducing the need to stop and reload the brush in mid stroke.
For more on bristle types, see Badger, Camel, China Bristle, Fitch, Nylon, Ox Hair, Polyester, Sable, Squirrel, and Taklon in the Dictionary of Finishing Terms.
Question: What is ebonizing?
Ebonizing is any process used to dye wood black. Wood can be colored black using paint, stain, black lacquer, black aniline dye, or iron acetate -- a homemade chemical dye. True ebonizing means using a dye rather than paint or black lacquer, so some of the wood grain shows through even though it is black. Ebonizing is done for several reasons, not least of which is the high cost of ebony and blackwood. Cherry ebonizes well, and is a good substitute for ebony. Ash is also popular, as it is inexpensive and its coarse grain adds texture to ebonized pieces.
Question: How do I ebonize wood?
Aniline dye is the easiest method; just use a concentrated black dye and let it soak in thoroughly before wiping off the excess. Another popular dye is iron acetate, or iron buff. This is made by shredding fine steel wool, then wetting it and allowing it to rust for a few days. The rusty steel wool is then soaked in about two cups of white vinegar for several days. Do not cover the vinegar solution, as gasses are produced that could cause a stopped bottle to explode. The resulting iron acetate solution is strained through a filter, then applied to the project the same day. Pre-treating the wood with tannin will produce the deep black desired when ebonizing; otherwise a weathered silvery gray tone is produced.
Question: What is a French polish?
French Polishing is mostly a technique for applying shellac in many thin coats, very similar to a padding technique. Usually, the first step is to apply one coat of linseed oil to the wood to bring out its full color. Next, 4F pumice and shellac are used to fill the pores of the wood. The pumice is clear when wet by the shellac, making it an ideal filler for any color of wood. After the filler coat or coats have dried, several bodying coats are applied. The first may be padded or brushed on, but later coats are applied using a polishing wad. This is made by wadding up a bit of cloth into a 1" ball, squirting in a bit of alcohol and a little 3lb cut shellac, then covering the ball with two layers of unwrinkled cloth, bringing all the corners to the top of the ball to make a handle. Several coats are padded on until the finish acquires a soft shine and has visible depth. The finish is allowed to cure for several days, then it is given a final buffing with a soft pad just barely dampened with alcohol. For more detailed information on how to apply a French polish, read any of the books in the recommended reading section.
"Popping" the Grain
Question: What is "popping the grain" and how do I do it?
Popping the grain is a technique used to highlight the figure of woods like
curly maple, mahogany, or cherry; or quilted or birdseye maple. The effect
looks best on light colored woods.
There are two ways to enhance figured woods. The simplest is to use linseed or tung oil. The oil is applied, then vigorously rubbed into the wood with a bare hand. This forces the oil deeper into the wood. Several coats of this treatment will produce a handsome effect and a soft, satiny sheen. The other technique uses dye. A first coat of very thin black dye gives the entire piece a medium gray tone. The wood is lightly sanded to remove most of the gray, and then a yellow to orange colored dye is used. The wood can then be topcoated with the finish of your choice.
Shelf Life of Finishes
Question: How long can I store finishes?
Most liquid finishing products have a shelf life, after which they may not cure properly. Shellac has the shortest, at about six months to a year at the most. Waterborne coatings have a shelf life of 1 ½ to 2 years, and most other finishes last several years. Dry shellac flakes have an indefinite shelf life, as does paste wax. Excessive heat, freezing, and allowing finishes to skin over in the can will greatly reduce their shelf life.
Question: I have a can of varnish that has sat on the shelf for several months. The varnish in the can has developed a skin over it. Is the varnish still good?
If the skin is thin, the varnish can probably be used, otherwise, leave the lid off and let it harden before throwing it out, to avoid any hazardous waste issues. If the skin is thin and flexible, remove it and stir the varnish thoroughly. Then brush a little onto a nonporous surface such as glass. If the finish hardens properly, check to see if the finish flowed out and covered the brush marks. If it didn't, a tablespoon or two of an appropriate solvent should fix this. Always strain varnish, new or old, into a separate container before using it. This removes any hard globs or foreign matter. Any paint store should carry paper strainer/funnels for this purpose.
Stain Pre-treater and Wood Conditioner.
Question: How can I tell if I need to use a conditioner before staining?
The only sure way is to test on scraps first. If you will be staining end grain, you'll almost certainly need to pre-treat the end grain.
Question: I stained the wood and it came out all splotchy. Now what do I do?
The only fix here is to sand off the stain. Then pre-treat a test sample and stain. If the sample comes out blotchy after pre-treating, try using a glazing technique instead.
Question: I need to stain a new cabinet to match my old ones. How do I do this?
The first step is to make certain that the old cabinet was actually stained. If the wood's pores are not significantly darker than the rest of the wood, either the wood was not stained or a dye was used. If the wood was stained, then it is simply a matter of finding the nearest color at your local finishing supplier, and possibly mixing in a little of another color of the same brand of stain to get a perfect match. Be aware, however, that different brands of stain may not be compatible when mixed together, even if both are oil based or waterborne. If a dye was used, or you simply want to match the patina of the old wood, the color matching process is the same as for stains; you just use aniline dye or tint the finish with universal tinting colors.
Question: I applied a stain / dye to my project and now I don't like the color. How do I remove the color?
Dyes, such as aniline dyes, can often be removed with household chlorine bleach. Just wipe on the bleach and let it dry. Any crystalline residue can then be simply brushed off the wood. Stains, since they contain (relatively) big particles of colored pigment, are more difficult to bleach. Try two-part wood bleach first, but if that fails stripper and a stiff plastic bristle brush may be the only solution.
Question: I applied a coat of polyurethane to my project yesterday, and when I came back today, it was still tacky. What should I do?
Wait. High humidity will often keep polyurethane tacky for days. Try stirring
the finish more thoroughly before your next coat, and maybe move to a warmer
and drier area with better ventilation.
If you are finishing rosewood (including kingwood and cocobolo) or teak, strip off the poly and seal the wood before re-coating. The oils in these woods prevent varnishes and lacquers from curing properly.
Question: I'm using the finish according to the manufacturer's instructions, but when it dries, the brush marks still show. How do I get a smooth finish?
Thin it. If you are using an oil base varnish, regardless of the manufacturer's instructions, you can thin it with an appropriate thinner or solvent. Add a tablespoon or so per quart and test on a nonporous surface such as glass. Add thinner a tablespoon at a time until the finish levels itself properly. If you are using a waterborne coating, you can thin it with water, but DO NOT thin it more than 15%, or the dispersants that make the finish do the magical things it does will become ineffective. If further thinning is necessary, use a product such as Flowtrol, available from professional finishing stores.
Waterborne vs. Oil Based Varnish
Question: Isn't oil based varnish tougher and more resistant to chemicals than waterborne varnish?
The short answer is 'barely'. Waterborne finishes have come a long way since they were first introduced, and the level of protection they offer is comparable to many of their oil base counterparts. In fact, a few products are better than the originals. Another factor to consider is the difference in cleanup and dry time. Cleanup of waterborne coatings is a simple matter of washing in warm, soapy water. Oil based products require cleanup with the appropriate solvent, then that same wash in warm soapy water. Most waterborne coatings dry faster than oil base coatings, especially polyurethanes. On a good finishing day, you can put four coats of waterborne polyurethane on a floor, versus three coats of oil base poly.
Question: How do I weather new wood to look like boards from an old barn?
Weathering wood is a similar process to distressing antiques, and has three basic steps: large distress such as cracks and gouges, small distress such as wormholes and natural wear, and coloring or patina. The large distress must be done in a realistic fashion, with only occasional large cracks and a few nail holes. Next add the smaller distress marks such as small wormholes and dents. Dents are best made with an odd shaped tool or rock, turning it and varying the force and angle of each blow. The characteristic weathered texture of wood can be replicated by scorching with a propane torch, then brushing with the grain with a wire brush. Play the torch lightly over the surface and be careful not to overdo the brushing. Finally, the silvery gray color can be imitated with an iron acetate solution, described above under ebonizing.
Question: I've heard you can make your own wiping varnish. How?
Simple. Just thin your favorite oil base polyurethane or varnish to a light syrup consistency with mineral spirits. The label may say 'do not thin' to comply with E. P. A. VOC restrictions, but don't worry, the finish can still be thinned. Some thinned finishes may congeal after a few weeks into an odd paste, so only mix what you can use in a couple of days.
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