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Urea-Formaldehyde and Resorcinol Glues - These glues are unequaled in all around performance. They have excellent water resistance, good gap-filling properties, sand extremely well, clean up with water and have the longest open time of most glues, approximately 20 to 30 minutes. They are creep-resistant and are used extensively in structural assemblies, veneering and production furniture shops. The downside is that they require longer clamping time - usually up to 12 hours. They also are sensitive to temperature and do not cure at temperatures below 70 degrees (65 degrees for Unibond, discussed below). They need to be carefully mixed in the proper ratio of resin to catalyst. The curing process releases small amounts of formaldehyde but this is a negligible amount. Some woodworkers may find the fumes irritating so it's a good idea to use these glues in well- ventilated areas and wear gloves when using. My favorite Urea-formaldehyde glue is Unibond 800 and I use it exclusively in my veneering work. This glue is sold as a modified Urea -formaldehyde and comes packaged as a liquid resin which is mixed with a powdered catalyst. The distinct advantage of this glue is that it contains no water, which is beneficial is veneering large and complicated assemblies. The powder comes in several colors, white, tan and brown so that the hard glue will match the wood being glued. Another manufacturer, Weldwood ,sells a UF glue called Weldwood Plastic Resin and the powder is mixed with water to activate it. This is an easy glue to use and is similar to glues used to bond plywood and structural beams. Don't use this glue for veneering - water makes the veneer curl. The glue can be colored by the addition of water-soluble dyes.
Resorcinol formaldehyde glues like Weldwood, have exceptional water resistance and are used in marine applications. I don't usually use them on furniture, as the glue mixes to a dark, reddish glue line, but on hidden joints like mortise and tenons this would not be a problem.