Q&A: Water-Based Urethane for Floors

A.Michael Purser responds: I am confident that water-based finishes will perform as well or better than oil-based products, if the installer takes the time to master some new application techniques. Waterborne finishes have been used for years in high-traffic areas, such as gyms and racquetball courts.

Waterborne floor finishes have a low viscosity — that is, they’re watery — so the finish penetrates deep into the wood. While this increases their durability it can also create some application problems that you’ve got to master.

For starters, the finish can really raise the grain on open-grained wood, such as oak. To combat this problem, I mist the floor very lightly with a two-gallon garden sprayer. I don’t allow the water to pool, and then I let the wood dry for about 12 hours (check with a moisture meter to be sure the moisture content has not been raised). This is sufficient to raise the grain, which I knock down with a worn screen back. If you do this before applying the first coat, you’ll avoid problems caused by excessive disking between coats.

Because you have less buildup, disk between coats with a light abrasive pad, instead of a screen back. These pads are color coded, and green seems to work best.

Also, coats of waterborne polyurethane are thin and dry quickly, so it’s important to keep a wet edge when laying them down. To make this happen, you may need to add a retarder (ask the coating manufacturer), and lower the heat and keep doors and windows closed to reduce air movement while applying the finish. Then allow the finish to dry as slowly as possible to cure it. Some finishes are marketed as quick-dry products, but ignore this marketing hype. The better the coat is cured, the stronger it will be.

Michael Purser is a second-generation floor finisher in Atlanta, Ga.