Open rafters and trusses are an endless source of falling dust. So if you’re working under an open ceiling, hang plastic sheeting above. Keep the plastic at least 12 in. from light fixtures or remove the bulbs. Sometimes, adding plastic “walls” is a lot easier than cleaning up the entire area. If you’re using oil-based finishes, hang the sheets about a foot from the floor to allow for ventilation.
Wet the floor
A floor dampened with a mop or spray bottle has two benefits: It prevents you from kicking up dust as you walk around. And it raised the humidity, so polyurethane dries slower and remains workable longer.
Declare war on dust
Airborne dust is the wood finisher’s nemesis. It settles on wet coatings and creates ugly pimples in the dried finish. You can sand them out, but it’s better to minimize that labor by minimizing dust sources. Clean up the work area and change out of the dusty clothes you wore while sanding.
Limit air movement
If you’re using water-based finishes, control airborne dust by turning off forced-air heating or cooling, and by closing windows and doors. This doesn’t apply to oil-based finishes; ventilation is required to remove harmful fumes.
Remove the legs
A disassembled table is much easier to move and the legs are easier to finish. On a typical table, removing each leg is as simple as unscrewing a nut.
A vacuum with a brush attachment will remove 99 percent of the sanding dust. But that’s not enough. This photo shows how much dust is left over. After vacuuming, wipe with a tack cloth (available at home centers) if you plan to use oil-based stain or coatings. If you’re using water-based finishes, use a lint-free rag dampened with mineral spirits.
Do a final sanding by hand
A random orbital sander is perfect for most of the sanding. But do a five-minute final sanding by hand using the same grit. Hand-sanding with the grain removes swirls and torn wood fibers left by the orbital action of the sander.
Sand every square inch the same
Any variation in sanding steps can show up in the final finish. If, for example, you run out of 80-grit sanding discs halfway through the initial sanding, you might be tempted to switch to 100-grit. But don’t. Even after sanding with higher grits, stain may look different in differently treated areas.
Most professionals we talked to stop at 150-grit on coarse-grain woods like oak or walnut and 180-grit on fine-grain woods like cherry or maple. But that doesn't apply to end grain. End grain shows sanding scratches more than face grain, so you may have to sand to 220- or even 320-grit.
Skip grits when sanding
You don’t have to use every available grit as you progress from coarse to fine. Instead, you can jump from 80-grit to 120- to 180-, skipping 100-and 150-grit.
Most common wood species— pine, birch, maple and cherry— absorb stain unevenly. For a more consistent finish, apply a pre-stain conditioner.
Inspect your sanding work
Stain will highlight any flaws in your sanding job (swirls or cross-grain scratches). Then you’ll have to resand— and sanding stained wood is a real pain. To find flaws before you stain, use low-angle light. Wiping on mineral spirits also helps to reveal problems.
There are lots of clear finishes. But for a combination of usability and durability, you can’t beat polyurethane. Oil-based poly, which dries slower than water-based, is best for beginners because it allows more working time. The other important difference is clarity: Water-based poly is absolutely colorless, while oil-based has an amber tone, which can be good or bad depending on the look you want.
Depending on the conditions, oil-based poly may become too sticky to work with after just five to ten minutes. Water-based poly dries even faster. So have all your supplies lined up and ready to go before you start. And once you’ve started, there’s no time for coffee or bathroom breaks.
Roll on oil-based poly
Coating a big surface with a brush—before the poly becomes gooey—requires speed and skill. Rolling, on the other hand, is faster, easier and almost goof-proof.
Rolled-on poly looks terrible at first, but the bubbles disappear in minutes, leaving a smoother surface than most of us can achieve with a brush. Beware of ridges formed by the edges of the roller and humps where you start and stop. You can minimize both of those flaws by applying lighter coats. We experimented with several kinds of rollers and got the best results with microfiber mini rollers. We also tried rolling on water-based poly; don’t do it.
Sand between coats
A quick hand-sanding between coats flattens our flaws before the next coat. Polyurethane tends to gum up sandpaper, so use paper or pads that resists clogging (320-grit). On shaped edges, use synthetic steel wool, such as Scotch-Brite pads, labeled "very fine."
Clean off the white stuff
As the table dries after wet-sanding, a white residue will appear. Be sure to clean it off completely. Residue left in the grain lines of coarse-grain wood will be trapped under the final coat and haunt you forever.
Don’t sand through
If you sand through the polyurethane and remove some stain, you can touch up with more stain. But the repair won't be perfect, so take pains to avoid that mistake. Sand very lightly after the first coat, just enough to remove the dust whiskers. After the second coat, you can sand a little harder to flatten larger flaws. Always be careful around the edges of the table; that's where it's easiest to sand through.
The deep grain lines in woods like oak or walnut will telegraph through the clear finish, no matter how many coats you apply. And that’s fine; it’s part of the character of coarse-grain woods. But if a perfectly smooth surface is the look you want, use a grain filler. You’ll find several products online or at woodworking stores. With most, you wipe on the filler, squeegee off the excess with a plastic putty knife and then sand after it’s dry for a smooth-as-glass surface.
Coat the underside
Wood absorbs moisture from the air, shrinking and swelling with changes in humidity. Polyurethane (or any coating) slows that absorption. So if you coat only the topside, the unfinished underside will shrink or swell at a different rate. That means a warped table. But one coat on the underside will stabilize the tabletop.
Apply at least three coats
With a thicker layer of protection, damage to the underlying wood is less likely—so your tabletop will look better longer, and reviving the finish will be easier. Some finishers apply four or even five coats.
Never use wax or polish
All you need for routine cleaning and care of your table is a damp cloth. When normal wear eventually dulls the finish, you can renew it in just a few minutes with another coat of wipe-on poly. But if you've ever used furniture wax or polish, a fresh coat of poly may not stick.
Seal end grain
The end grain of wood soaks up finishes and often turns much darker than the face grain. Check for this on your test block. If you get an ugly result, pretreat the end grain with a dose of finish that will limit absorption (wood conditioner, sanding sealer, shellac or polyurethane thinned 50 percent). Apply the treatment with an artist’s brush and be careful not to slop onto the face grain.