Popular Woodworking 2008-06 № 169, страница 65
Sanding. The most efficient sandpaper grits to use vary with the situation. It's inefficient, for example, to begin sanding withtt 80 or #1 00 grit on this pre-sanded veneered plywood. The # 120-grit sandpaper I'm using here is coarse enough to be efficient and doesn 'I create more work.
The only thing you can do in finishing that can't be fixed fairly easily is to blotch the wood with a stain.
The purpose of this rule is to encourage you to relax about finishing; you can't "ruin" your project unless you're staining a blotchy wood, such as pine, cherry or birch. All problems other than blotching can be fixed, with the worst case being you have to strip off the finish and begin again. Professional finishers know from sad experience that having to strip and start over is not that uncommon. It's equivalent to the woodworker's distress over having to make a new part because of cutting a board too short.
To fix blotching, you have to sand, scrape or plane the wood to below the depth the stain has penetrated.
To avoid blotching, the stain has to be kept from penetrating. Do this using a gel stain or by partially sealing the wood with a thinned finish called a" washcoat." An example is wood conditioner, which is varnish thinned with two parts mineral spirits. Be sure to let whichever washcoat you use dry thoroughly (six or eight hours for wood conditioner) or it won't eliminate the blotching.
The first coat of any finish seals the wood; all additional coats are topcoats.
This rule is important for understanding that products labeled or promoted as "sealers" don't seal the wood any better than the finish itself. They are used to solve a problem.
Sanding sealers contain a soap-like lubricant that reduces sandpaper clogging, making the sanding of varnishes and lacquers easier
and faster. Sanding sealers are great for production situations but offer little advantage for most home or small-shop projects, especially when you can get similar easy sanding by thinning the first coat by half with the appropriate thinner. In fact, sanding sealers weaken water resistance (because ofthe soap) and the bonding of the topcoat, so it's better not to use them unless you have a big project.
Shellac is effective as a barrier against silicone and odors (refinishing problems), and pine resin and the oil in oily woods such as teak and rosewood. These substances can interfere with the (low and dry ing of finishes. But there's no reason to use shellac as the first coat if the wood you're finishing doesn't have one of these problems.
Of course, shellac is an excellent finish in its own right and can be used effectively for all the coats.
Apply a wet coat of stain and wipe off the excess before it dries.
This is the basic instruction for applying
all stains. As long as the wood is not naturally blotchy, and as long as it has been prepared well (all the milling marks and other flaws are sanded out), this method of stain application will produce an even coloring.
Confusion has been introduced by the Minwax ad on television, which shows brushing thick coats of stain and not wiping off the excess. This procedure cannot produce an even coloring.
To get a darker coloring, you can leave a stain on the wood for a while to allow some of the thinner to evaporate, essentially increasing the colorant-to-binder ratio. Then wipe off the excess. You can also leave a little of the excess, called a "dirty wipe," or apply a second coat of stain after the first has dried.
But in all cases, unless you're spraying the stain, you have to wipe off most or all the excess to get an even coloring. PW
Adams School of Woodworking near Indianapolis, Ind., lune 21-22. Visit marcadams.com or call317-535-4013 to register, or for more information.
Blotching. Some woods, such as the pine shown here, blotch when stained. Blotching is the only situation in finishing that can't be fixed fairly easily, with stripping and starting over being the
Sealing. Sanding sealers contain a soap-like lubricant that causes the finish to powder so it doesn't clog the sandpaper. But sanding sealers don't seal the wood any better than the finish itself and, in fact, weaken water resistance and the bond ofthe finish.
Staining. As long as you wipe off excess stain, the coloring will always be even unless the wood is naturally blotchy or, as with this oak, the grain is highlighted.
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