Q. We have a customer who is hot pressing hardwood plywood and is getting telegraphing of veneer tape through the face veneer. The veneer tape is buried in the glueline. The customer insists that we "test" a sample of the plywood with the telegraphing.
A: Several comments: The common procedure is to press faces with the tape up and then sand it off later. Why isn’t this being done?
There is a tape that can be pressed tape down in the glueline, but I am not in favor of using it, even though it saves a little on sanding; it is a 34 gram, three-hole tape, which is approximately one-half the thickness of the standard 40 gram tape. I wonder if the heavier tape is being used. Check this.
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Another possibility is that the color difference between the taped and untaped areas will fade after a few hours of exposure to sunlight. Cherry’s color is sensitive to light.
Cherry's color is also very sensitive to acids and bases. For example, contact with a caustic material can cause a “blood red” color. My first guess is that the tape is preventing uniform absorption of the glue (The glue’s pH may have a slight effect on the color.), so the color change at the tape, with less glue adsorption, will be different than the rest of the piece. Try putting a piece of plastic near the tape to create the same blocking effect and see if that also shows a color difference. This is my first guess.
Another test would be to avoid spreading adhesive in certain spots (make some sort of pattern with no adhesive) and then press and check for the glue spread pattern showing through. This would clearly show if it is the adhesive.