From Flawless Staining
A fine finish is the crowning touch that brings out the beauty of wood, but finishing wood is tricky business. Even master woodworkers get a little nervous when the time comes to finish their projects. That’s why they don’t rush the job. Bitter experience has taught them that extra attention to the key steps in the process saves time and trouble. This article will describe those key steps, warn you about some common pitfalls and offer tips for a smooth, successful finish.Sand With The Grain
Sand with the grain when hand-sanding or using a belt sander. Scratches are hard to see when they run parallel to the grain. But even the lightest scratches across the grain are obvious, especially after staining.
Hand-Sand the Curves
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Sand curved surfaces—and other areas an electric sander
can’t reach—by hand. Treat all areas equally, using the same progression of
sandpaper grits for both hand and power sanding.
Progress from coarse to finer and finer sandpaper. Whether you’re sanding by hand or using a power tool, start with 80-grit to sand away blemishes, then use 120-grit and finally 180-grit. Using these exact grits isn’t vital (100-150-180 works too), but it’s important to progress in steps, removing deeper scratches and leaving finer scratches each time.
Don’t Sand Through the Stain
When sanding between coats, it’s easy to rub right
through the clear coat, removing the stain below. So sand super lightly after
the first coat, just enough to cut down any dust whiskers on the surface. If
there are bigger problems—such as runs—deal with them after the second coat
when you can sand a bit harder. To repair rubbed-through spots, just apply new
stain. Immediately wipe away any stain that gets on the surrounding
polyurethane.
Sand Without Leaving Scratches
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A random orbital sander leaves scratches that are
practically invisible, so you can sand across joints where grain changes
direction. But move slowly (about 1 inch per second) and apply light pressure.
Otherwise, you’ll get swirly scratches (above).
Watch for Blotchy Wood
Some woods absorb stain unevenly, which causes dark
blotches to appear. Birch, maple, pine and cherry can all play this ugly trick
on you. It’s hard to eliminate this effect, but you can limit it by applying a
wood conditioner before staining. Conditioner also prevents wood’s end grain
from absorbing more stain than the face grain. Get a quart at a home center for
about $8.
Sand Curves With Pad
When sanding between coats, smooth curves with a steel wool substitute such as 3M’s Scotchbrite pads. Steel wool leaves fibers behind, which can cause stains in the finish.
Better Brushes Are the Key
Usually, a brush is the best tool for applying
polyurethane. For water-based poly, a synthetic brush (such as nylon or
polyester) is best. For oil-based poly, use a natural-bristle brush. In either
case, plan to spend at least $10 for a good-quality brush. Quality brushes hold
more finish, lay it on smoothly and are less likely to leave lost bristles in
your clear coat. If you clean your brush immediately after use, it’ll serve you
well far into the future.
Dust settling on wet polyurethane will give your finish the look and feel of razor stubble. So clean the area you’re working in and let the dust settle. Then dust the workpiece with a soft, lint-free cloth. Don’t use tack cloth—it can leave a residue that interferes with adhesion.
Leave Mistakes Alone (Usually)
When you notice a run, missed spot or other problem in
the polyurethane you applied minutes earlier, you’ll be tempted to brush it
out. Don’t. The finish may look wet, but chances are it’s already sticky, and
brushing will only make a mess. There are a couple of exceptions to this rule:
You can pop tiny air bubbles with a pin, and you can pluck out a hair, a lost
bristle or unfortunate fly using sharp tweezers and a steady
hand.
Sand Between Coats
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Lightly sand between coats with 400-grit wet/dry
sandpaper, which won’t fall apart when it gets wet. A little water provides
lubrication and keeps the finish from clogging the paper. Sanding after each
coat (except the last) rubs out imperfections and roughens the surface for
better adhesion of the next coat. In most cases, this is a quick job, more like
wiping the surface than sanding it. When the sanding is done, wipe away the
residue with a damp rag.
Inspect Before You Stain
Turn out the lights and shine light at a low angle across the wood to reveal imperfections. Flag the problem areas with masking tape and sand them out.
Wipe Instead Of Brush
Wipe oil-based polyurethane onto hard-to-brush surfaces
using a soft, lint-free cloth. Wiping leaves a thinner coat than brushing, so
you’ll have to apply more coats. Water-based poly becomes sticky too fast for
wiping.
Test Stains, Thoroughly!
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You can’t rely on those stain samples on display in stores. Actual color varies a lot, depending on the type of wood and how you prepared it for finishing. So save scraps from your project, run them through the same sanding process and use them to test finishes. If you didn’t build the item you’re finishing, run tests on an inconspicuous area—the underside of a table, for example. Test stain on scraps to get the color you want. Leaving excess stain on the wood for longer or shorter periods won’t affect the color much. If it’s a custom color you’re after, you can mix stains of the same brand.
Test Clear Finishes, Too
Water-based polyurethane affects the color only slightly.
Oil-based poly has an amber tone that can dramatically change the color of
stained or unstained wood. The same stain was used on the samples
shown.
Use a Pad on Large Areas
Apply water-based polyurethane to large surfaces fast by
using a paint pad. Water-based poly dries quickly and may not allow enough
“wet” time for brushing out big areas.