A polyurethane finish brings out the natural beauty of wood grain and protects the wood from moisture and scarring. Although not as durable as lacquer or shellac finishes, polyurethane is the most common choice for individuals who refinish wood themselves. That is because polyurethane doesn't require specialized spray equipment, a spray booth or the exceptional brush skills of an experienced finisher. Polyurethane is made in oil-based and water-based formulas, and both formulas are available in a spray or brush-on form. Every option has pros and cons. Brushing skill, patience level and use of the tables will help you decide which kind of clear polyurethane will work for your tabletops.
Water-based polyurethanes tend to cost a bit more than oil-based polyurethanes, but the difference is minor if you need only a small amount. The cost difference becomes more apparent in large projects because more coats of water-based polyurethanes are necessary to provide the same level of protection as fewer coats of oil-based polyurethanes. A small end table could be finished with one can of water-based polyurethane that would cost only a few dollars more than oil-based polyurethane. If you want to finish a large, multileaf dining room table, however, you would need multiple cans, making water-based polyurethane the more expensive of the two kinds by a moderate margin.
Both water-based and oil-based polyurethanes can be brushed or sprayed. The water-based formulas are thinner than the oil-based formulas, and so they are more prone to drips and runs. They also may show more brush marks. Oil-based formulas may bubble more often than the water-based formulas if proper technique isn't practiced. If your brush skills aren't up to par, the spray can varieties give you a better chance at a flawless coat, but the finish is more likely to come out uneven across large areas such as tabletops due to overlapping spray strokes. The best option may be to use a spray for tables' legs to avoid drips along turned areas and to use a brush-on formula on tabletops for a smoother finish. Oil-based formulas produce a very noxious odor, which is a consideration if your project area has inadequate ventilation.
Despite the fact that both finishes are clear, the color of the finished product is very different depending on which product you use. An oil-based product adds a warm amber tint to wood and accentuates its grain, and a water-based formula dries crystal-clear with no color enhancement. Warm-colored wood such as maple looks better with the oil-based amber tint. Very pale wood, including pine and aspen, may look cleaner with the colorless water-based finish. See the wood swatches in the stain aisle at your home-improvement store to assess the difference.
Oil-based polyurethane provides a stronger, more protective finish than water-based polyurethane, but applying extra coats of the water-based polyurethane can result in equal protection. Although a table may require two or three coats of an oil-based polyurethane, the same table may need four or more coats of a water-based polyurethane. The hardness of the final cured finish is about the same between the two kinds of polyurethane, but the hardness may vary slightly among brands. A very hard finish scratches more easily than a softer finish; a finish that is too soft, however, gouges easily. Follow the curing instructions on the polyurethane can to reduce the chance of marring the finish.
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