One-part polyurethane wood adhesives comprise a new class of general purpos
e consumer products. Manufacturers' claims of waterproof bonds brought many
inquiries to the Forest Products Laboratory (FPL) from users constructing
aircraft, boats, lawn furniture, and other laminated materials for outdoor
use. Although FPL has technical information on several types of polyurethan
e and isocyanate-based adhesives for wood, no information was available on
this new class of adhesives. Four commercial polyurethane adhesives, along
with a resorcinol-formaldehyde adhesive to represent a standard of performa
nce, were subjected to a series of industry-accepted tests that assess vary
ing levels of bond strength and durability. In bonds to yellow birch and Do
uglas-fir, the polyurethanes did not differ significantly from each other i
n their performance, as a group, though, their dry shear strengths showed t
hat they were significantly stronger than the resorcinol. Dry wood failures
by the polyurethanes were high and did not differ significantly from the r
esorcinol. After three water-saturating procedures, wet shear strengths of
polyurethanes and the resorcinol were statistically comparable. Wet wood fa
ilures, however, were very low among polyurethanes, which is a sharp contra
st to the high wood failure by the resorcinol. A moderately severe delamina
tion test indicated varying levels of water resistance among the polyuretha
nes, but the resorcinol was completely resistant to delamination. A very se
vere cyclic delamination test caused severe delamination of polyurethane bo
nds. However, a recently discovered hydroxymethylated resorcinol (HMR) coup
ling agent dramatically increased delamination resistance of polyurethane a
dhesives. Ln a test of resistance to deformation under static loads, polyur
ethane bonds withstood extreme exposures of temperature and relative humidi
ty for 60 days without deformation.