Top it Off

While early American floors were left natural and occasionally cleaned with sand or lye and water, most of us today prefer some sort of topcoat on a wood floor. Finishes are usually blends of natural plant or nut-based resins or oils suspended in or mixed with oil, alcohol, solvents, or water that cure to a hardened finish.

The most popular finishes are polyurethanes. Easier to apply, they last for years before they need refreshing. Whether water based or oil based, polyurethanes require multiple coats (with sanding in between) for durability. Waterbased finishes dry quickly— hours between coats, ready for use in a couple of days—but they lack some of the depth of oil-based polys and such traditional treatments as tung oil (see “Oil vs. Water,” p. 41). Refinishing a water- or oilbased polyurethane requires sanding the old finish before applying new.

Oil-modified polyurethanes are compositionally similar to water-based polys, except that the resins are impreg- nated with oil. Drying times are much longer, at least 24 hours and sometimes several days per coat. Oil-based polys cure to a deep, durable, and abrasion-resistant finish with a slight amber color that approximates period varnish. While water-based polys clean up with soap and water, oilbased ones require solvents to clean hands and brushes.

Tung oils and oil-impregnated tung oils penetrate rather than float on the surface of the wood. Like oil-modified urethanes, tung oils require longer drying times between coats, but they produce a true period appearance. Tung oils must be thinned with a solvent before use; Real Milk Paint offers an already thinned version called Half & Half that does the work for you. While polymerized tung oils dry faster than pure ones, a tung-oil floor usually takes 30 days to fully cure and should be treated carefully for the first few months.

Best of all, tung oil and low-VOC finishes made from natural proteins can also be refreshed with new coats without stripping. No sanding is required between coats, either.