MY FINISHING SCHEDULE
Often we hear or read about different steps, or approaches, to use in the finishing process, but are left with more questions than answers. “Should I do this before that, or after?” “When do I need to use this step, and what determines if I use it or not?” I certainly don’t have all the answers, but I can share the sequence of steps I follow in finishing. Not all steps are necessary for every finish, and I often skip one or more. But if a step is to be used, I try to do it in this order.
PREPARATION: Depending on wood species and final finish to be applied, sanding through at least 220 grit is a must for me. For high gloss finishes (lacquer, shellac, varnish, etc.) I sand through at least 320. Between the final two sandings, I use a sponge or wet cloth to wet the surface with water and raise the grain, then sand again. I use a “raking” light to view the surface and ensure all scratches have been removed. Small dents, gouges, or depressions in the wood can be raised by placing a wet cloth over the area and applying heat with a clothes iron.
BLEACHING: Used to lighten wood prior to applying a stain. There may be several reasons to lighten wood. You may prefer a light (or blond) look for the piece you are making. Scandinavian (aka Swedish or Norwegian) furniture is often very light in color. Also, if the piece you’re finishing has a blemish, or dark spot that distracts from the overall appearance, you may want to lighten it for a better match to the surrounding areas.
PRE-STAINING or SAP-STAINING: When both heart (dark) and sap (light) wood are present and a uniform color is desired in the finished piece. Only the sapwood is stained to make it match the heart wood. This step is done prior to actually staining or coloring the entire piece so that you start with a uniform color throughout.
STAINING or COLORING: To change the color, tone, or shade of the wood. Aesthetically, I prefer the natural look and color of most woods, and would rather not do anything to alter that. There are, however, times when a color change is called for, and that’s when this step comes into play. My preferred method of coloring wood is water-soluble dye. I start with a powder, mix it in warm water, usually apply it with a soft rag (spraying and brushing are also acceptable), and then reapply to achieve the desired color. There are a number of other dye formulations (e.g. alcohol and oil based) available, and all are equally effective. The “best” one is the one you are most comfortable using. (A note about water-soluble dyes: after the water evaporates from the wood, the color you see IS NOT the color you will end up with. A clear top-coat will change the color, sometimes significantly, so experiment on a scrap piece and complete the entire finishing process before settling on a color. Also, water in the dye raises the grain, so you will need to lightly re-sand to smooth it back out.)
Occasionally I use a stain to alter the color of wood. When I do, I prefer an oil based Non-Grain Raising (NGR) stain, with no sealer or topcoat included. Apply liberally, let it sit for a few minutes, then wipe off any excess. If a darker color is desired, reapply. If you use a product with a sealer or topcoat (e.g. polyurethane) included, a second coat is less effective as the topcoat in the first application blocks the pigment in the second application from getting into the wood.
WASHCOAT: A very thin coat of shellac (sometimes lacquer sealer) applied over a stain to keep the stain from bleeding into a filler or the next coat in the finishing process. A washcoat can also be used on woods prone to blotching (e.g. cherry or pine) prior to staining to give the finish a uniform appearance. In this case, it is sometimes referred to as a “sizing coat”. I prefer shellac in a 1 lb. cut, or less. Sand very lightly with 320-grit paper / 0000 steel wool or finer after washcoating.
FILLING: Use a liquid or paste filler to fill the pores of open grain woods, providing a smooth surface for later topcoats. A liquid filler (e.g. shellac or lacquer) can be used on species with moderately open grain (e.g. birch, gum, cherry, maple, etc.). For species with a more open grain (e.g. oak, walnut, mahogany) use a paste filler. Fillers can be tinted with stain.
SEALING: Same as washcoating above, but when applied over a filler it is referred to as a “sealer”. If no filler is used, this step may be skipped.
GLAZING: Applying a separate finish to add highlights to specific areas of a piece. Often used to simulate age and wear, or “antiquing”.
TOPCOAT: A film like finish applied after all staining, coloring, filling, and sealing has been completed. Good topcoat materials include varnish, polyurethane, lacquer, and even shellac, and can be applied by brushing, wiping, or spraying. Most topcoats do not penetrate into the pores of the wood, but rather lay on the surface like a film. When the carriers/solvents evaporate, or cure by polymerization, a hard surface coating remains which protects the wood. Different topcoat materials offer different levels of protection.
Topcoat materials can be classified in one of two categories: Solvent release or reactive. Solvent-release finishes form a hard film on the surface as the solvent or thinner evaporates. There is no chemical change in the make-up of the original material. Reactive finishes “cure” by chemical reaction. As the wet film absorbs oxygen, the liquid gradually changes to a solid. Solvent-release finishes can be repaired fairly easily. The solvent in each successive application tends to dissolve the previous layer, and blends in. Reactive finishes are much more difficult to repair. In most cases, the cured layer will have to be removed before another layer can blend in.
Solvent release finishes include:
Shellac: Good working and wearing characteristics. Serves well as an undercoating for varnish, polyurethane, and lacquer. Should not be used for table tops as it will dissolve if it comes in contact with any form of alcohol, and has a tendency to turn white and become soft if it comes in contact with water containing an alkali. Dries very quickly as the solvents evaporate, leaving only the resin.
Lacquer: A coating material containing various cellulose resins and plasticizers dispersed in a complex, volatile solvent. Dries very quickly after application due to evaporation of the solvents. Can be pigmented and used for toning. The pigment (stain) stays in the finish and lays on top of the surface much like paint. Pigmented lacquers can be used for exteriors.
Reactive finishes include:
Varnish / Polyurethane: Clear, transparent coating material. Consist of natural or synthetic resins (the solid portion of the finish), vehicles (oils), solvents, and driers. “Long Oil” varnishes (often sold as “Spar” Varnish) contain a large portion of oil. They are slow drying but produce a very tough, wear-resistant surface. Excellent for exterior uses. “Short Oil” varnishes contain a small portion of oil, dry quickly, are hard and brittle, and leave a higher luster. More often used for furniture and interior finishes. In general, varnishes provide excellent hardness and flexibility, while resisting abrasion, chemicals, harsh cleaners, oils, and moisture. Over time they tend to darken and leave a yellow or amber tone. (Note: water-based polyurethane does not yellow over time. It remains clear.)
Oil: Usually either Boiled Linseed Oil (BLO) or Tung Oil wiped onto the surface with a soft cloth. Can be either wiped on in a thin layer, or flooded on for a few minutes, then wiped off. For most woods, oil finishes provide a deeper, richer tone than other top coats used alone. To me, it seems to add a little “age” to a piece. Oils alone provide a low to moderate level of protection. Personally, I almost never use oil as my primary topcoat material. One thing to consider: if you plan to use oil, and then an additional topcoat (e.g. varnish, polyurethane, etc.) it’s usually easier to combine the two into one step. Read on!
Oil/Varnish: A wipe on finish consisting of some type of oil blended with varnish. Commercially available under several brand names. I prefer to mix my own with equal parts of varnish or polyurethane, boiled linseed oil or tung oil, and thinner or turpentine. (Note: thinner dries much quicker than turpentine.) Apply liberally to bare wood using either a brush or cloth. Watch for dry spots and reapply as needed to keep a wet surface. When dry spots no longer occur, usually after 10-15 minutes, wipe off with a soft cloth. Finish wiping in the direction of the grain. Reapply when completely dry, usually after 24 hours. At least three coats are necessary for a durable finish. If necessary or desirable, topcoat with shellac or varnish.
Wiping Varnish: Similar to Oil/Varnish, but without the oil. Mix equal parts of varnish or polyurethane with mineral spirits or paint thinner. It can be wiped on in multiple thin layers to build up a durable finish. Or it can be flooded on, then wiped off after a few minutes. This approach leaves more material on the surface with each application, and usually requires fewer coats than the “wipe on” method. Wiping varnishes can be premixed, but why pay a premium for something you can easily mix yourself.
My hybrid approach: I often use a hybrid of the two finishes discussed above. I’ll first apply a liberal coat of an oil/varnish, keeping the surface wet for about 10 minutes, then wipe it off. The oil (either BLO or Tung) gives the wood a deeper, richer tone than the varnish alone. But once the first coat has completely dried, or cured, I don’t feel that successive coats of oil are going to add that much to the final appearance. So I switch to a wiping varnish, without the oil. At this point, I’m just building up the protective coating and luster of the finish.
As I mentioned at the beginning, this is MY approach. That doesn’t mean it is the only way to do it, or even the right way to do it. I welcome comments from others, especially those who are much more knowledgeable about finishing than myself. In fact, each of the steps or procedures above could easily be expanded into a separate article. Hint! Hint!