Sanding vs. screening
When a wood floor loses its luster, the usual solution is to sand it down to raw wood and completely refinish it. But often, that’s the wrong solution.
All wood floors are protected by a clear coating that eventually becomes scratched, scuffed and dull. But as long as the damage is shallow—in the coating and not in the wood itself—you can renew the floor by adding a new coat of polyurethane right over the old finish.
This article will show you how to do just that. As with any wood-finishing project, 90 percent of this job is preparation. You have to thoroughly clean the floor, touch up any deep scratches and roughen the existing finish with sanding screens so the new finish will adhere well. Expect to spend at least one full day on this prep work. The recoating itself usually takes less than an hour.
Recoating takes a lot less time, skill and money than full-scale sanding and refinishing. And although roughing up the existing finish creates plenty of dust, it’s still much less messy than sanding down to bare wood. There’s another advantage: Every time you sand a floor down to bare wood, you remove some of the wood. A solid wood floor can be sanded several times before that’s a problem. But laminated floors (glue-down or floating floors) have only a thin layer of good-looking wood veneer over a plywood-like base. The veneer can be sanded once or twice—after that, sanding will expose the plywood core beneath.
Where recoating won’t work
The type of flooring you have doesn’t matter. Recoating works on solid wood, laminated wood and parquet floors alike. But a new coat of polyurethane may not stick to your existing finish.
If your floor’s finish was applied before the 1970s, it’s probably wax, old-fashioned varnish or shellac. No new finish will stick to a wax finish or any other finish that’s ever had wax applied to it. Polyurethane might adhere to an old, unwaxed varnish or shellac finish. But these finishes do wear out, and since they’re probably more than 30 years old, it’s best to sand them off and start over.
In fact, if you have an old finish from the days before polyurethane, your only alternative to sanding is wax. If the floor is in fair condition, wax can restore the shine. A wood flooring dealer can recommend a suitable product. Wax is easy to use, but not very durable. You’ll probably have to rewax every six months or so.
Even if the existing finish is polyurethane, good adhesion isn’t a sure thing. Residue from all kinds of household chemicals, such as furniture polish, glass cleaner, insecticide and wallpaper paste, can interfere with adhesion. Since you can’t know for certain all the potions that have landed on your floor, you must test for adhesion before you recoat your floor.
Step 1: Test for adhesion
Photo 1: Prepare test areas
Roughen up two test areas and then coat them with urethane.
Photo 2: Suitable for refinishing
Check the adhesion by scraping a coin across the finish.
Photo 3: Not suitable for refinishing
If the finish flakes easily or is cracked or has an orange-peel look, you’ll need to sand before refinishing the hardwood floor.
Pick at least two test areas on the floor: one in a high-traffic zone, the other along a wall or in a closet. Clean each area with a wood floor cleaner and roughen a 6 x 6-in. area with sanding screen. Then wipe away the sanding residue, mask around the test area, and give it a coat of polyurethane (Photo 1).
After 24 hours, take a look at the polyurethane. Aside from a few tiny “whiskers” caused by dust particles, it should be smooth. Then scrape the polyurethane with a coin. Press down firmly, but not too hard—even a sound finish might scrape off if you press as hard as you can (Photo 2).
If the polyurethane is smooth and doesn’t scrape off with moderate pressure, your test is a success and you can recoat the floor.
But if the polyurethane flakes off as you scrape, or if the surface has a crackled or orange-peel texture (Photo 3), there’s something on the old finish preventing the new finish from adhering properly. That “something” could be furniture polish, residue from window cleaner or a hundred other things. But whatever it is, there’s only one solution: You have to sand down to bare wood and completely refinish the floor.
Step 2: Money and materials
Recoating a typical floor (200 sq. ft. or so) is about half the cost of sanding and refinishing it. Most of the cost goes for tools and renting the buffer, so recoating floors in two rooms costs only a few bucks more than recoating one room.
All the tools and materials for this project are available at home centers. Wood flooring dealers also carry most of these products. Here’s what you’ll need:
- A liquid floor cleaner formulated specifically for wood floors.
- Scouring pads (a.k.a. “synthetic steel wool”) to remove marks on the floor. Scotchbrite is one common brand. Regular steel wool will also work, but don’t use steel wool if you plan to use a water-based finish; the tiny particles of steel left behind will cause rust stains.
- A 2- or 3-in. bristle brush made specifically for applying varnish and other clear coatings. Use natural bristle for oil or synthetic bristle for water-based.
- A finish applicator pad designed to apply floor finishes (Photo 12). You can buy a long handle that screws into the applicator, but any push broom handle will work. Some applicators are made for oil-based finishes; others are made for water-based products. Check the label.
- A respirator that has organic vapor cartridges to filter out harmful fumes (Photo 10) while you’re using mineral spirits and oil-based polyurethane. These respirators are pricey, but absolutely necessary.
- A gallon of mineral spirits, 100-grit sanding screen and a dust mask.
- A buffer (Photo 9), which you can find at a rental center or flooring store. You’ll also need a buffing pad (made from synthetic mesh) and sanding screen discs (the same material used to roughen the floor by hand). The screens are available in several grits. Use 150- or 120-grit if available. They’re less likely to cut through the finish into the wood than 100-grit. Get at least three screens for a typical room. You can return any you don’t use.
TIP: The buffer is a heavy, powerful machine. Learn to control it by practicing on a smooth concrete floor, using only the pad.
Step 3: Clean the floor
Photo 4: Clean the floor using a wood flooring cleaner
A dull putty knife is handy for scraping up petrified chewing gum and other gunk. For tough marks, use a scouring pad dampened with mineral spirits. If that fails, try sanding screen. As you clean, use pieces of masking tape to mark any deep scratches, ridges or areas where the finish has worn away. You’ll have to give these trouble spots special attention (see “Problems Areas” below).
Photo 5: Roughen corners by hand
Roughen the existing finish along walls and in corners where the buffer can’t reach. The purpose is only to scratch up the finish, not to wear it down—or worse, sand right through it. Three or four passes with the sanding screen are usually enough. Wear gloves to protect your hands from the abrasive screen.
Photo 6: Set the buffer on the sanding screen
The screen isn’t attached to the buffer at all, but stays put under the weight of the machine. The screen will wear out after 10 to 15 minutes of use. When it does, flip it over or start with a new screen. Check the screen for grit every few minutes and wipe away any large particles that might scratch the floor. Note: Be sure to lock the buffer’s adjustable handle in place before you begin buffing.
As you’re cleaning, you may find deep scratches that go through the finish and into the wood. You usually can’t make these scratches disappear completely, but you can make them a lot less noticeable. If your floor is as light or lighter than the floor shown here, first wet the scratch with mineral spirits. A wet coat of mineral spirits produces approximately the same look as a coat of polyurethane. And on a light-colored floor, it might darken the scratch just enough to
If that doesn’t work, apply some wood stain to the scratch using a cotton swab. Because the scratch is rough and porous, it will absorb a lot of stain. So begin experimenting with a stain that’s much lighter than the tone of your floor and wipe away the excess stain right after you apply it. For best results, use two stain colors to match the light and dark patterns in the wood grain (Photo 7).
If your floor has a high-traffic area where the clear finish is completely worn away, wet the area with mineral spirits to see what it will look like with a coat of polyurethane. If it looks good, clean the area thoroughly, apply a coat of polyurethane and give it at least two days to cure. Then you can buff and recoat the new polyurethane along with the rest of the floor.
Look out for ridges. The buffer will eat right through the finish down to bare wood at high spots. And if your floor is colored with wood stain, you’ll be left with light-colored strips where the stain has been rubbed off. Photo 8 shows how a solid-wood floor can buckle in high humidity. But smaller ridges, where the wood strips cup slightly or one plank sits a bit higher than the next, can cause just as much trouble.
If you can flatten a ridge by standing on it, fasten it down with a finishing nail or two. If you can’t flatten the ridge, you’ll have to roughen the area by hand using sanding screen. And remember to avoid that area
with the buffer.
Stains that have penetrated through the finish as well as the wood can only be removed by sanding. But there’s no harm in recoating over them—if you can live with them.
Step 4: Buff the floor
Photo 9: Swing the buffer back and forth
Buff the old finish with a fresh sanding screen.
Photo 10: Clean up the sawdust
Vacuum thoroughly, then wipe the floor with mineral spirits to remove all the sanding dust.
Buff the floor starting at one wall and moving backward across the room. Slowly swing the buffer left and right as you go. Pass over each area only once or twice so you don’t cut through the finish. To make the buffer swing to your right, gently lift the handle. To swing left, lower the handle. To control dust, place fans in open windows, close ducts, seal off the work area and wear a dust mask.
Clean the room thoroughly, beginning with windowsills, moldings and any other surface where dust might gather. Vacuum the floor, then wipe it with a rag dampened with mineral spirits. The rag should be lint-free and should not have been washed with a fabric softener, which can interfere with the polyurethane’s adhesion.
IMPORTANT: Make the room as dust-free as you possibly can. Dust that settles on the wet polyurethane will create tiny craters or bumps.
Step 5: Choose a finish
Photo 11: Start at the wall
Cut in along the first wall with a high-quality brush. Use a natural bristle brush for oil-based urethane or a synthetic brush for water-based urethane.
Photo 12: Use an applicator pad
Apply polyurethane using an applicator pad attached to a long handle. When spreading the finish, you can dip the applicator into a paint tray filled with polyurethane, but a cardboard box lined with a plastic bag is less likely to tip over. To smooth the finish, first “unload” the pad by pressing it hard against a dry part of the floor. Then drag the applicator lightly across the floor from one end of the room to the other.
The best floor finish for a do-it-yourselfer is polyurethane. Other floor finishes are either less durable or much more difficult to work with. You’ll find two types of polyurethane at home centers:
The oil-based polyurethanes (or “oil-modified urethanes”) are easier to apply because they dry slowly, giving you more time to spread and smooth the finish. They have a yellowish hue and slowly darken with time, which may be good or bad depending on the look you want. The big drawback to oil-based products is the nasty vapor they give off. You must open windows and wear a respirator.
Water-based polyurethanes (or “water-borne urethanes”) are generally a bit more durable than oil-based versions. They have a milky color when wet, but they dry crystal clear and remain clear. The milky color makes them easy to see, so you’re less likely to miss spots. Still, water-based products are harder to apply because they dry fast.
NOTE: With either type of polyurethane, be sure it’s recommended for wood floors before you buy.
Required Tools for this Project
Have the necessary tools for this DIY project lined up before you start—you’ll save time and frustration.
- Dust mask
- Knee pads
- Painters tape
- Putty knife
- Roller tray
- Shop vacuum
You’ll also need a floor buffer, buffing pad, sanding screens, finish applicator pad, a respirator for organic vapors, and a window fan.
Required Materials for this Project
Avoid last-minute shopping trips by having all your materials ready ahead of time. Here’s a list.
- Liquid floor cleaner
- Mineral spirits
- Polyurethane floor finish
- Sanding screen (for drywall)
- Synthetic steel wool pads