Polyurethane Finish Alert

by Larry Swan, USDA Forest Service, Winema National Forest
from the Western Juniper Newsletter, Vol. 2, No. 1, Summer 1997.

A painter recently reported a problem with a polyurethane product used to finish western junipervstair tread in a custom-built, multi-million dollar home in Walla Walla, WA. The juniper wasvkiln-dried (MC<14%), resawn, book-matched, and predominantly heartwood.

One coat of the "interior satin-polyurethane clear varnish" (company's tech sheet description) was brushed on straight from the can. After about a day or so, patches of whitish haze formed around some knots and on the end grain. It could not be sanded-out. One-coat of ultra Poly KoteTM interior satin-polyurethane finish was applied. The whitish spots appeared to "disappear".

Tests were conducted at Kellstrom Brothers Paint Center, Klamath Falls, with both polyurethane products. One coat of the initial product used in Walla Walla yielded similar results - a patchy whitish haze around some knots. A second coat appeared to make the haze "disappear". One coat of the Poly KoteTM polyurethane product did not produce the patchy whitish haze around knots. Tests were replicated on three different interior panel segments with similar results.

One test panel has been sent to the manufacturer of the product which produced the whitish haze around knots (major brand name) and one to the U.S. Forest Service, Forest Products Lab (Madison, WI.). Their analysis and comments will be reported in a future newsletter.

It should be noted that the directions for the product which produced the whitish haze state that a sealer-primer should be applied to all bare wood surfaces before application of their polyurethane product. This may have prevented the problem. The Poly KoteTM product does not make the same recommendation. Both products make specific recommendations about what kind or how to prime paste wood fillers used under polyurethane finishes. (see Wood Filler Alert! in the Summer, 1996 - Western Juniper Newsletter [Vol. 1, No. 2]).


The Western Juniper Steering Committee appreciates the professionalism and cooperation of Kellstrom Brothers Paint Center, and thanks them for their assistance.

For more information, contact Larry Swan, USDA Forest Service, Winema National Forest (541-883-6714).