The winter months in North America are often problematic for gluing applications.
Problems generally arise as a result of cold, dry weather. Poor glue lines can occur when the temperature falls below the adhesive's specific minimum use temperature. Also during the winter, dry conditions in a shop can cause open joints.
PVAs (white and yellow glues) have a range of minimum use temperatures between approximately 38° F and 60° F. Most standard PVAs fall in the low end of this range, while cross-linking PVAs generally fall in the higher end.
When PVAs are used below the minimum use temperature, a "chalked" glueline will usually occur. This appears as a chalky substance and will have little or no strength. Keep in mind that the adhesive, the ambient temperature, the gluing equipment and the material to be glued must be kept above the minimum use temperature in order to avoid chalking. Because of the insulating quality of wood, the core of a stack of lumber can remain at very cold temperatures even after being inside for 2-3 weeks.
Other adhesives are also affected by low temperatures. Urea Resins and Resorcinol Resins won't cure below 70° F and open time on hot melts is significantly shortened at lower temperatures.
Not surprisingly, frozen glue is often a concern during the winter months. Normally, most standard PVAs are freeze thaw stable. They are usually tested to withstand a freeze/thaw cycle of five times. Most manufacturers publish this information on their technical data sheets. If frozen glue is received, it must be thawed at room temperature and stirred. If, at this point, it appears the glue has separated, contact the adhesive supplier for replacement.
Other adhesives are not as stable. Some cross-link PVAs are freeze/thaw stable and others are not. Contact cements are not freeze/thaw stable. Once frozen they can not be used. If in doubt, be sure to check with your supplier. Reactive Polyurethanes are not affected by cold temperatures (within reason).
The other problem associated with colder weather is related to moisture content. Often, the MC of wood received can be as high as 10%. In a heated shop, the moisture content of the air is nearly zero. After gluing, the wood seeks to equalize its moisture content with that of its surroundings. In a low moisture environment the wood loses moisture quickly and shrinking occurs, often resulting in open joints at the ends of panels. It is a very good idea to invest in a humidification system for your shop no matter what its size. Contact your adhesive supplier for exact specifications.
Jeff Pitcher is Marketing Director for Custom-Pak Adhesives in Newark, Ohio.