Q: We are having some problems with veneer adhesion to our MDF substrate. After we have completed the panel and finished it, we notice delamination (a raised bump) in a few areas in the center. What should we be looking for?
A: From your brief description, I would conclude that you have what some might call bubbles in the veneer. I suspect that you are using a solvent-based adhesive for laminating. These adhesives will emit gas for a while; this is sometimes called off-gassing.
If you get the finish on rapidly after gluing, the finish helps seal in this gas and so pressure develops that pops the veneer from the substrate. In fact, it is possible that the finish is also reacting with the adhesive to encourage off-gassing.
Your adhesive and finish supplies need to talk to each other. But, I would suggest that a PVA adhesive for laminating might be the best choice. Otherwise, allow several weeks between laminating and finishing (which is not often possible).
Of course, as with all gluing, we do need to make sure that the surfaces are flat, freshly prepared and free of wax (I always suggest a very light one-touch sanding of MDF panels just before gluing to achieve fresh wood and therefore achieve the maximum strength joint).
You must also have short assembly time, proper spread rate and uniform spreading of the adhesive, adequate pressure, and so on.
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