Ending With a Good Finish
Polyurethane is the most popular finish for floors. It's tough enough to handle constant traffic and is resistant to almost everything. There are two types of polyurethane finish: oil-based (solvent borne) and water-based (waterborne).
Oil-based or water-based? Each type has its strengths, and neither is a poor choice. Oil-based polyurethane will turn a light amber color with age whereas water-based stays clear. If you want to preserve the creamy-white look of maple, for instance, use waterborne polyurethane. (For a red-oak floor or a stained floor, use either type of finish.) Another advantage of waterborne polyurethane is how quickly it dries — you can apply two coats in three hours and walk on the floor in your socks after seven hours. However, because it dries quickly, you must work fast to maintain a "wet edge" during application or you'll end up with visible lap marks where wet polyurethane was applied over dried or partially dried finish. And you can't go back and work waterborne polyurethane, even when it's wet, or you'll leave marks in the finish.
Oil-based polyurethane dries slowly, which means you can't walk on the finished area for 24 hours or more after coating. It also emits noxious fumes. But it can be worked when wet, which means you can go back and correct mistakes — a crucial advantage for the beginner.
As for durability, Lance Hemsarth, technical director for Minwax, a leading maker of polyurethane, maintains that oil-based polyurethane is still the standard for performance, especially for high-traffic areas.
Water-based polyurethane runs about $40 per gallon, enough to cover 600 square feet of floor space. A gallon of oil-based poly costs around $25, enough for 400 square feet. In either case, follow the manufacturer's application instructions carefully.
Finish pointers. Before applying any finish, vacuum twice and use a tack rag on the entire floor.
For edges and corners, use a painting pad to apply a water-based finish; on open floor, use a synthetic-wool applicator.
With an oil-based finish, use a china-bristle brush for edges and corners and a lamb's-wool applicator for open floor.
As you apply the finish, move the applicator with the grain of the wood from wall to wall, angling it slightly.
For a truly smooth finish, sand lightly between coats with a pole sander using 100-grit sandpaper. Then use the vacuum and tack rag again with care before adding another coat of finish. Don't sand the final coat — just appreciate how it reflects the light and know that you have a finish that will last for years. 
