Working With Polyurethane Adhesives
Polyurethane glues are versatile, and can be used in many situations where you might select an epoxy, such as bent lamination work, and bonding dissimilar materials or oily exotic woods. Here are some guidelines for working with them successfully.
What is the clamping time for polyurethane glues?
Clamping time is a minimum of 2 hours, depending on ambient temperature and humidity as well as the porosity of the substrates. For best results, leave assemblies in clamps at least overnight.
How much clamping force should I use?
Use moderate clamping force (about 30 to 60 psi at the point of contact). Do not overclamp, especially with dense hardwoods, as this may cause too much glue loss due to squeeze-out.
What is the open assembly time?
Minimum of 20 minutes at room temperature and 50% humidity, making it a good choice for complicated assemblies.
What is the best way to clean up squeeze-out?
The foamy squeeze-out has no strength and is easily removed with a sharp chisel or scraper.
Does polyurethane adhesive permit creep?
PU doesn’t allow joint creep because it is completely rigid after curing. The glue line is not affected by temperature changes and will not become brittle with time.
Does polyurethane glue accept wood stain?
Polyurethanes accept wood stains more readily than most adhesives; however, water-based aniline stains do not soak into this glue nearly as well. Excess glue should not leave spots, but if you notice a spot while applying a stain, lightly sand it and continue staining.
Can I use polyurethane adhesives for outdoor projects?
PU will easily endure the regular soakings and high humidity to which outdoor projects are exposed.
Are polyurethanes waterproof?
Gorilla Glue is water-resistant and not for continuous submersion. Akfix PA370 conforms to D4 classification, the highest level of waterproofing by European grading standards, making it suitable for complete immersion, even in marine applications below the waterline.
Can I use polyurethane glues in cold conditions?
To ensure proper curing and flowout, PUs require a temperature above 40°F (5°C) and work best at 68°F (20°C).
Do PUs need moisture to cure?
Yes, water is the catalyst for curing. In dry conditions or when working with wood that has a low moisture content (<10%), it’s good practice to brush or spritz water on one side of each joint.
