Q. In hot weather, we are noticing that we are getting some poor gluing at times. We do keep our adhesive refrigerated slightly to avoid getting it too hot. We try to keep the [plant cool too, but it is hard on hot days. What else should be look at doing?
A. Your implied thinking that the temperature of the adhesive will affect joint quality is correct. In fact, many glue companies make a wintertime and a summertime glue mix. The reason is that when adhesive is hot, it becomes thinner and more runny. Hence, it may run out of the joint before you get the pressure on. Also, heat makes the adhesive cure more quickly. So, the idea of keeping the adhesive cool before you use it is great.
However, what about the wood temperature? Is the wood quite hot, especially if it was recently from a storage area that is hot? Hot wood will quickly heat and thin the cool adhesive. You should be getting the pressure on within 20 to 30 seconds after the glue is spread to avoid thinning and also some precure of the adhesive. If the heat of the wood causes some precure, the adhesive will not be squeezed into the tiny nooks and crannies in the wood surface; the end result is a weaker joint.
Although our bodies tell us that it is hot and humid, you do need to check the humidity in storage and in the plant with an electronic instrument (get a small measuring unit costing $30 from an electronics store). It may surprise you to see that when the heat is over 100F, the humidity is often under 30 percent RH. If the wood is not also equally dry (about 6 to 7 percent MC), the wood can shrink a bit before you glue it, especially if you are gluing small pieces together. Small pieces change MC faster than large pieces as there is more surface area. This shrinkage will likely give you gaps in the glue joint over 0.006 inch which will give a weaker joint with most adhesives.
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