From the manufacturer:
Titebond 821 PREMIUM URETHANE WOOD FLOORING ADHESIVE is a high-performance formula ideal for bonding engineered and solid plank flooring, solid plank flooring and bamboo to common underlayments and subfloors. Its non-slumping characteristics, not available in other urethane adhesives, allow the troweled ridges to bridge normal gaps between the wood flooring and the subfloor, virtually eliminating hollow and popping spots. It also offers excellent green grab and develops a superior bond that will remain flexible for the lifetime of the floor.
Titebond 821 Premium is a moisture-resistant adhesive that allows the installer to wet lay the wood flooring without the traditional risks of solvent- and water-based adhesives. In addition, it is mold and mildew resistant.
Titebond 821 Premium delivers exceptional performance characteristics that exceed the expectations of professional installers.
• #8129 - 3.5 gallons
• Non-slump formula
• Superior green grab
• Long open time
• Easy cleanup
• Highly moisture-resistant
• Will not cause dimensional changes in wood flooring
• Excellent bond strength
• Mold and mildew resistant
• No flash time required
• Ideal for above-, on- and below-grade installations
• Unaffected by freezing temperatures
• 95% solids
• Contains no water