Q: What's the ideal ambient temperature and humidity level for a veneer gluing operation? We've heard about 50 percent relative humidity, but we're having difficulty maintaining it; our workers don't like the warm temperatures. What's the ideal balance?
A: You can use any temperature that you want. However, the glue must be compatible with such temperature levels ... sometimes wintertime and summertime glues are used.
Perhaps even more important is the RH. We want to use an RH that's close to the conditions that the veneer will be exposed to in any subsequent processing and eventually to the humidity conditions in use. The eventual average in-use humidity condition in most of the United States and Canada inside a home or office is 37 percent RH. However, because shrinkage is almost more of a problem than slight swelling, often we target 30 to 35 percent RH in the wintertime. In the summer, unless you have an a/c, you take what you get.
I hear this 50 percent value quoted once in a while. The truth is that in a high humidity condition, any small cracks in the veneer (or in lumber, for that matter) will swell shut and become invisible until the RH drops later. Also, high humidity will avoid any problems due to poor drying (high moisture content, that is); such problems will show up when the conditions dry out, which typically will be after the product is finished and maybe sold. So, high RH just delays any problems. I'd rather find out if I'm going to have veneer checks or other problems before I put too much labor into the veneer (or lumber).
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