DEAR TIM: What type of finish was used on hardwood floors circa 1964? Does it need to removed or screened to apply a new finish such as oil or water-based urethane? Jim Heavey
DEAR JIM: Although highly unlikely, it is possible your finish is urethane. Urethanes were developed in the early 1960's. The widespread adoption of urethanes for floor finishes didn't start to happen until the late 1960's and the early 1970's.
In all likelihood, the finish on your floor is traditional varnish. It is hard to discern the difference between the two with the naked eye, but you can test in a small out-of-the-way location. A large drop or spot of water will often turn varnish cloudy within 30 minutes or less. Urethane, on the other hand, is usually unaffected by water.
The bigger problem might be the presence of lead in the varnish. Yes, lead was sometimes added to clear finishes years ago. I would absolutely perform a lead test on the finish before I would create clouds of sanding or screening dust.
Furthermore, it is also possible a past owner of the home applied wax to the finish. If wax is present, you must remove it before you do any application of a new urethane. The screening process will not remove all of the wax, if it is present. Screening is the same as a light sanding and is meant to lightly scuff an existing surface to ensure a good bond between an older glossy surface and the fresh coat of floor finish.
