PURPOSE: To produce a water-resistant adhesive polymerized, crosslinked and thermally cured under heating and pressure and withstading boiling from a water-soluble resin material.

CONSTITUTION: A finely divided lignocellulose material is brought into contact with high pressure steam for a sufficient time necessary for decomposing and hydrolyzing hemicellulose to obtain a water-soluble low mol.wt. resin material to separate the water-soluble resin material. The residue of the once hydrolyzed lignocellulose material is again rapidly brought into contact with high temp. and high pressure steam sufficient to decompose and hydrolyze the residue without carbonizing cellulose for a sufficient time to obtain a water-soluble resin material. The water-soluble resin material is applied to a surface to be bonded to be heated and pressed under a temp. and time condition sufficient to generate polymerization, crosslinking and thermosetting and to form a water- resistant adhesive layer on the surface to be bonded.