Q. I have a customer who is using Titebond 50 to glue hard maple. He is edge gluing the stock, applying the adhesive with a felt roller on a taylor conveyer. After application, he is placing the stock in a taylor clamp carrier. Wood moisture and shop temperature seem okay.
The problem is that as the stock passes over the roller, the glue does not appear to be contacting the wood in spots. There have been some cases where the glue seems to "roll" back off of areas that it has contacted, as if there was silicone or some type of oil on the wood. The roller appears fine as far as roundness, amount of spread and condition of felt.
The customer cleans the pan on the roller about once a month. It is usually just covered with a damp rag at the end of each day.
A. Maple is notoriously easy to "glaze" or burnish if your blades are at all dull. This would be the best area to check first. Any spots that this occurs on would not allow the adhesive to "wet" the surface, resulting in the effect you described.
Surface wetting is very important in gluing. Think of it in terms of a freshly waxed car. If you put water on the surface of the car, it beads up. The water is not "wetting" the surface of the car. The same holds true in adhesives. It is absolutely necessary for the adhesive to wet the surface if a good bond is to be obtained.
Also, keep in mind that the best joints result from freshly machined stock. Assuming that your joints are true your best bet is to look at the condition of the surface to be glued.
Editor's note: This question was also sent to Professor Gene Wengert, Department of Forestry, University of Wisconsin, Madison, WI. His answer follows.
The adhesive comes with a chemical that improves wettability, so it would be extremely rare that the problem is with the glue. Rather, look for contamination of the wood.
Next time it happens, wipe off all the glue from the edge and then sand the wood slightly and try again. If the glue covers, then look for some oil that is on the planer/molder knives, conveyors, etc.
The other alternative is that the wood has been heated to destroy its wetting, but that would show up as a dark color. Again, the sandpaper test would cure the problem. Next time, let the glue dry and send me a sample.
Jeff Pitcher is Marketing Director for Custom-Pak Adhesives in Newark, Ohio.