Achieving a High Quality Wood Finish - Part II
Achieving a High Quality Wood Finish - Part II
Choosing a Finish
I use nitrocellulose lacquer for all my projects because I own spray equipment and lacquer was made to be sprayed. Even without spray equipment, however, there are several compelling reasons to use lacquer.
First, lacquer dries very fast, leaving almost no time for dust to settle onto the finish. This reduces the need for a perfectly clean finishing environment, though this is still desirable. For the spray finisher this has the added benefit of eliminating the need to mask everything in sight since any over-spray that reaches nearby objects is dry and can be simply dusted off. Because lacquer dries so fast, you can apply many coats in a very short time. I usually wait no more than 20-30 minutes between coats.
Second, lacquer cures by the evaporation of its solvent rather than by chemical reaction (like varnish or polyurethane) or not at all (like oil finishes). This means that a less than ideal temperature will not affect the ultimate hardness of the finish, though it may affect drying time. The fact that lacquer is solvent-based also means that each coat dissolves and bonds to the one beneath it, eliminating the need to sand between coats to get them to adhere.
Third, lacquer dries hard, making it very easy to polish to exactly the luster desired. Other finishes like varnish and polyurethane that cure by chemical reaction never completely harden; you may have to wait weeks or even months to do your final rubbing and even then you may not get the result you want. And because lacquer dries so fast you can rub a lacquer topcoat the same day it is applied, though ideally you should wait at least a full day. These properties also make lacquer very forgiving. If you botch a coat, simply wait for it to dry polish out the mistake.
Fourth, lacquer is very durable. Polyurethane exceeds lacquer in its ability to withstand abuse and water damage, and is therefore better suited to high-use surfaces, but damaged lacquer is much easier to repair.
Finally, lacquer in unparalleled in its depth and clarity. Nothing else even comes close.
Lacquer does have several disadvantages. Lacquer must be rubbed out to achieve the desired level of finish. This is one of the reasons for the appeal of mass market finishes such as varnish and poly that give reasonably good results right out of the can. However, once it is rubbed out, lacquer surpasses all other finishes in gloss, depth, and clarity. To get a truly high quality finish you must be willing to perform this extra step.
Because it dries so fast, lacquer does not brush well, another reason for the mass market preference for varnish and poly. There are, however, several ways around this. You can spray it, which is the ideal solution. A good HVLP (high volume, low pressure) spray outfit, which is what I own, can be had for just a few hundred dollars, and is well worth the investment if you do a lot of finishing. There are other alternatives, however, that make brushing feasible. First, you can add a little lacquer retarder to the mix to slow drying and allow the finish time to flow out. Second, you can purchase lacquers specifically designed for brushing (called "brushing lacquers"). Third, you can apply many, many coats, accepting the brush marks, and simply cut down through them when you rub out the finish.
Lacquer’s most significant disadvantage is that its fumes are very toxic. For this reason you should always wear a NIOSH-approved vapor respirator when you use lacquer. NIOSH-approved vapor respirators have special carbon filter elements that absorb organic fumes; read the package carefully..
The toxicity of lacquer, its solvent, and its fumes, have caused many finishers have stopped using them. Lacquer poses little threat to the environment, it is so volatile, it evaporates almost immediately if spilled, and because lacquer thinner is a naturally-derived organic compound, once airborne it is rapidly broken down by sunlight into benign compounds. The only significant danger lacquer poses is if you breathe its fumes directly because you failed to wear your respirator.
Many books have been written about finishes and their advantages and disadvantages and I’ve read most of them. My conclusion is that the advantages of using lacquer far outweigh its disadvantages. It is easier to use and repair, more forgiving, and more beautiful than any other finish. As I’ve said before, nothing else even comes close.
Applying sanding sealer
Bare or dyed wood should be sealed before applying your topcoat. Sealing fills the grain and any remaining sanding scratches and helps the finish adhere. Though you can use the topcoat itself to do this, I prefer to use a dedicated lacquer sanding sealer because it is specially formulated for this purpose and sands easily. Apply two to three coats and sand to a uniform sheen with 400 grit paper, being careful not to cut through to the dyed wood. Remember to use a sanding block on flat surfaces. Wipe away the dust.
Applying the topcoat
Each coat of lacquer is very thin. Therefore you will need to several coats to give you enough of a build to rub out the finish without cutting through it.
If you want to be able to feel the texture of the grain through the finish, apply only two to three coats, just enough to allow you to rub the finish to a satin sheen with steel wool without cutting through. Because brushed lacquer tends to be uneven and require a lot of rubbing, I would recommend spraying in this case.
If you want a high-style finish, apply eight to ten coats to give plenty of material to rub out. Wait a couple of days for it to dry completely.
Rubbing out the Finish
Now for the really satisfying part: you are ready to rub out the finish. To do this you will work your way up through successively finer grits until you achieve the desired level of luster. Start with 400 grit wet-or-dry paper lubricated liberally with mineral spirits. On flat areas remember to use your sanding block to ensure the surface is perfectly level. Sand through any brush marks, dirt, or other flaws in the finish. Sand in the direction of the grain until you acquire an even sheen. Wet lubricant may conceal flaws so dry the surface to check it. Repeat with 600 grit, 000 steel wool, and 0000 steel wool, wiping down the piece to remove all traces of the previous grit and re-lubricating with fresh mineral spirits each time.
Be careful not to cut through the finish, especially on edges. If you do cut through to bare wood you will have to stop and carefully reapply some dye and finish before continuing.
If a satin sheen is desired, 000 or 0000 steel wool is as far as you need to go. Clean off and wax your piece and congratulate yourself on a job well done (see below). If, however, you desire a high gloss, continue with a soft cloth and rottenstone lubricated with mineral spirits. Rottenstone, a very fine polishing powder designed for furniture finishing, is available at woodworking supply stores, but white automotive rubbing compound from your local auto supply store will work too. Finally, wipe down the piece and finish with a good automotive polishing wax, following the directions on the bottle.
You will want to clean and wax your piece periodically to maintain the finish. I use Murphy’s oil soap or a mild household cleaner to remove surface dirt and film, and then I wax with Johnson’s paste wax. Don’t use sprays they must stay wet to look good and tend to attract dust and emphasize streaks and fingerprints.
It is easy to see why one-third the price of a high-quality piece of furniture is in the finish. Professional shops can afford to be more automated, but they still follow this same procedure and must rely on elbow grease on all but flat surfaces. You can see, though, that there is no mystery to achieving a high-style finish. The process may seem somewhat arduous but it really goes rather quickly. And the final result is so immensely satisfying you’ll wonder why you ever bothered with mass-market finishes.
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