Wood finishing tips. Most woodworkers and woodturners will apply some type of finish to their pieces. Applying a finish can enhance the appearance of the wood and help to protect the wood. Part of the protection comes from stabilizing the moisture content in the wood. The moisture content of a finished piece will vary less throughout the year. This will help reduce cracking in the wood because of the stresses from the wood shrinking and swelling.
The first step in creating a good finish is to prepare the surface. Most finishes will highlight torn grain, tool marks, and sanding scratches making these flaws even more obvious. Today, woodworkers will find there is a wide selection of finishing products available. These products include (waxes, oils, stains, dyes, polyurethane, shellac, and paint). All finishes have their strengths and weaknesses. The goal is to find a finish that 1) applies easily, 2) enhances the appearance, 3) provides a durable protection, and 4) cleans up easily. Below are some helpful tips on wood finishing.
1. Avoid applying one heavy coat of a finish.
To speed up the drying process and improve the final appearance, manufactures of clear finishes recommend applying multiple light coats. Furthermore, most experts recommend that you apply finishes on a dry day. Preferably when temperatures are above 70°F (21°C), with adequate ventilation.
2. Wait until the finish has cured before using.
Do not confuse “Dry to Touch Time”, “Dry Time” and “Recoat Time”. The “Cure Time” means the coat is in a fully finished state. On the other hand, “Dry to Touch Time” is the time it takes the finish to become tack-free. “Dry Time” (also called “Recoat Time”) is the recommended length of time between coats of the product.
3. Avoid applying a clear finish on top of wax.
Most finishes will not properly adhere to wax (e.g., lacquer, polyurethane, shellac, varnish). The wax seals the pores of the wood so the clear finish cannot penetrate and bond. If after applying wax, you decide you would rather have a clear finish, you first need to strip the wax. After removing the wax, lightly sand the piece and then apply the clear finish.
4. Make sure to wait until walnut oil has completely dried before applying a clear finish.
Walnut oil is a very slow drying oil. It can often take weeks or months before for the oil to cure. If you apply a finish within 12-24 hours after applying walnut oil, the finish will seal off the oxygen. At which point, the walnut oil might never dry.
5. Avoid mineral oil if you are looking for an oil which will dry.
Mineral oil is a non-drying oil and will not change to a solid film. Even after months of drying, the oil will slowly seep out of the wood and into a paper towel. If looking for an oil that will dry, consider nut oils (including linseed oil, tung oil, and walnut oil). These oils will change from a liquid to a solid film when exposed to air for a period of time.
6. Feel free to apply wax over other finishes.
A wax will give finishes like varnish, polyurethane, lacquer, and shellac a soft luster and a smooth feel. A wax will add shine to the surface by filling in small voids and scratches.
7. Stain pieces before you apply polyurethane or sanding sealer.
Polyurethane and sanding sealer completely seal the wood. This prevents the wood from absorbing stain.
8. Avoid shaking a can of polyurethane.
“Shaking” a can of polyurethane to rotate the product will create bubbles. Instead, “stir” the polyurethane to rotate the product from the bottom to the top of the can. If bubbles do appear, you can typically remove them by brushing lightly over the finish – shortly after applying the product.
9. Consider stopping with 240-grits sandpaper.
Sanding beyond 240-grit results in a surface with poorer adhesion. Most finishes grab on to the “tooth” of a surface. Sanding beyond 240 grit can create a surface that is so smooth that the wood has no “tooth”. This makes it difficult for the wood to hold a clear finish like polyurethane.
10. Experiment on sample pieces
– when applying an oil-based finishes to exotic woods. Some exotic woods contain compounds that can leach into an applied oil-based finish. These compounds or antioxidants prevent the necessary chemical reaction from occurring. Without this reaction, the finish may remain tacky forever.
11. Consider using sanding sealer to speed up the finishing process.
Most sanding sealers will dry in one hour or less. So rather than waiting a day for the first coat of polyurethane to dry, by applying a sanding sealer, you can get a jump on the second and maybe final coat. Sanding sealer is also good for porous woods that tend to soak up the first few coats of a topcoat. Unlike other topcoats, sanding sealer builds up quickly and sands very easy. Sanding sealer can also provide a barrier so stain does not seep into the topcoat.
12. Mix only enough milk paint powder for the current project.
Once the milk paint powder has been mixed with water, it will slowly begin losing its bonding strength. Even if sealed in an airtight container, the mixed milk paint will begin to gel and harden in days. On the other hand, milk paint powder will last indefinitely.
13. Give water-based finishes a try.
One big advantage of water-based finishes is easier cleanup. Brushes, spills, hands, clean up with water! However, oil-based finishes must be cleaned with a solvent (mineral spirits, paint thinner, etc.) Some people feel the term “water-based” has been a hindrance to many finishing products. After all, how can a finish that cleans up with water provide adequate protection? A deeper look into water-based products and you will find that they contain a resin (e.g. polyurethane) that is suspended in water, along with a slow drying solvent. It is this solvent and not the water that performs the curing process. Today, many water-based products on the market provide as good as or better appearance and durability than their oil based counter products. I should mention the thinning and clean-up solvent for “water-based stains” and “water-based dyes” is water.
14. Use alcohol-based dyes, if looking for a quick drying option
. Water-based dyes typically take longer to dry than alcohol-based dyes. Expect to wait 4 to 12 hours for water-based dyes to dry. (Note: you can reduce the drying time for water-based dyes by applying the heat from a hair dryer). On the other hand, alcohol-based dyes might be dry in minutes. Some woodworkers will even use a lighted match to dry the dye/alcohol mixture. Be careful!
15. Experiment with dyes which can be mixed with either water, alcohol, or both.
One example, of a dye which can be mixed with either water, alcohol, or both is TransTint™. Some woodworkers like to mix these dyes with a 50/50 mixture of water and alcohol. This mixture raises the grain less than an all water mixture and dries quicker. Woodworkers also report it is more colorfast than an all alcohol mixture. You can also add TransTint™ to water-based stains to change the color.
16. Know what the term “organic solvents” means
The term “organic food” means food that is produced without manufactured fertilizers, pesticides, growth hormones, etc. However, the term “organic solvents” are a class of compounds which contain at least one carbon and hydrogen atom. Denatured alcohol, lacquer thinners, and mineral spirits are all examples of organic solvents.
17. Know when to use water-soluble dyes.
You might want to use water-soluble dyes if you anticipate you might later like a darken or lighten finish. Water-soluble dye stains contain no binder. This allows you to darken or lighten the color even after the dye has dried. To lighten the color, simply wipe a wet cloth over the dye. To darken the color, apply an additional coat. You can even apply a different colored dye to change the color.
18. Consider using stains that contain dyes.
If you wish to avoid stirring the product before use consider using stains which contain dyes. Pigments and dyes are the two most common coloring agents found in stains. Some stains contain only pigments, some contain only dyes, and some contain both pigments and dyes. Once mixed, dyes completely dissolve and you do not need to stir them again. However, pigments will separate or sink to the bottom of the container and will require stirring.
19. Realize the first application of stains will add the most color.
Oil stains contain a binder, which helps the pigments stay on the wood. This binder forms a thin film over top of the wood. This film partially seals the wood, resulting in the wood absorbing less and less stain on subsequent applications.
See Easy Approach to Wood Finishing for tips on how to simply your selection of finishes.
20. Avoid using a soft cloth when applying a finish on a lathe.
If an old T-shirt is caught on the rotating lathe, a finger might be what is torn away. If you insist on using a cloth, never wrap it around your hand or fingers. Instead, of using cloth rags, most experts recommend using paper towels or safety cloths (made from unwoven paper). If a paper towel catches on the chuck, faceplate, or piece being turned, it will just tear away. Note: look for “lint free” or “virtually lint free” paper towels. This will help keep short, fine fibers from showing in the finish.