Polyurethane is tough, durable and ideal for high-traffic areas or furniture that receives lots of wear and tear. You have two types of polyurethane to choose from; water and oil-based -- and both are good choices.
Oil-based polyurethane is a traditional finish, imparting a softer appearance, almost like a glow. Water-based is more contemporary, harder and leaves a glassy, hard appearance.
Water-Based or Waterborne
Finishes that clean up with water are often referred to as water-based -- but it's a bit misleading. If the finish were actually water-based, it would wash off when cleaned with water.
**_Waterborne finishes_ provides a more accurate description**. Water-based or waterborne finishes are composed of resin suspended in water and solvent.
The water evaporates from the resins as it dries, changing the finish from a liquid into a film.
Honey or Clear
Oil-based polyurethane cures when solvents evaporate from the mixture, allowing the resins and oil to harden. The hardening process can turn oils and resins a light honey color as it ages.
**Use an oil-based finish to add character to oak to give it a warm glow**. Water-based finishes remain clear as they age.
Preserve the pale, off-white appearance of maple -- or any natural finish -- by using water-based finishes instead.
**Water-based polyurethane dries quicker than oil-based products**. You can apply two water-based coats in three hours compared with oil-based finishes that require between 12 and 24 hours before applying a new coat.
Because water-based finishes dry quickly, you must work faster to avoid visible lap marks where wet polyurethane is applied over newly dried. After it's dry, you can't go back over it until it fully cures, or you'll leave marks in the finish.
Oil-based is more forgiving, allowing more time for correcting mistakes -- and that's important if you're a novice.
The debate over durability is contentious. **Oil-based offers more flexibility to withstand the natural expansion and contraction of wood, but it scratches easier than acyclic polyurethanes do**.
Water-based acrylic polyurethane won't flex as much, and it resists scratches. But if scratches do appear, they're more visible because of its glassy finish.
Cost and Coverage
Water-based polyurethane will cost you about $40 to $60 per gallon -- at the time of publication -- and covers about 600 square feet. A gallon of oil-based sells for about $25 and covers about 400 square feet.
Water-based products go on thinner than oil-based ones. Typical water-based products contain about 30 to 35 percent solids.
Oil-based products contain about 45 to 50 percent solids. **Solids create the tough protective finish, so you need to apply four coats of water-based to get the same protection as two or three oil-based coats**.
Handling and Application
Because water-based finishes dry fast, it's possible to apply several thin coats in a day and walk on the floor that evening. With the thicker composition of oil-based, you can only apply one coat, and then need to wait at least 24 hours before adding another coat.
**Sanding between coats of oil-based finish is typically required for the smoothest finish**. Higher-grit sandpaper, 220 to 400 grit, is best for sanding between coats.
Sand the dried finish only enough to smooth it, and don't sand after the last coat. Sanding sponges offer another option for sanding between coats.
VOCs or volatile organic compounds are fumes. The amount can differ by manufacturer, but as a general rule, **oil-based emits VOC fumes at a higher level than water-based** products do.
Look for warnings or check with the dealer to purchase low-VOC products. High-dollar, low-VOC finishes don't flow as easily and require more expertise to apply.