Friday, July 6, 2012

Veneer - Substrate and glue

I’ve heard a lot of misinformation about gluing veneer, particularly regarding the type of glue you should be using. The absolute worst glue you can use on a veneer project is contact cement. I’m amazed at how often I see some magazine advise using contact cement for veneer, or worse yet, occasionally on a woodworking television show. Contact cement is formulated to be used with rigid material like formica. Contact cement does not form a rigid glue line and always maintains a certain amount of flex or give to it. White and yellow glues are better, but still do not result in a rigid glue line. Additionally, the working time for white or yellow glues is relatively short and you have to work quickly before the glue sets up. The best glue for working with veneer is one of a family of glues based on urea formaldehyde because it has a relatively long open time and cures based on a catalytic reaction.


I’ve used a product called Unibond800 for years and have great success with it. Unibond800 has the unique characteristic of an absolutely rigid glue line after curing. This makes this glue ideal not only for veneer but also for bentwood lamination work. When using it for bentwood lamination, I experience virtually no spring back after removing the work piece from the glue form.

It does have a couple of drawbacks. First, it has a relatively short shelf life of about 6 months to a year, depending upon the temperature you’re storing it at. And second, since you add a catalyst powder to the glue, you must use whatever you mix because whatever is left will cure rock hard. Third, and this is a relatively minor one, the glue cures best in a warmer environment. If you are doing a glue up and the temperature is below 70 degrees, you need to cover the project with a heating blanket, or else the glue might not set at all.

The substrate you choose needs to be perfectly flat, free from any voids or surface defects, and as free from seasonal wood movement as possible. Plywood is an excellent choice, but you need to select high quality plywood that is free from internal voids. MDF is a wonderful substrate for veneer because it is dead flat, free from any internal voids, and will not change dimensions seasonally.


The picture above is a piece of MDF that I’ve applied 3/8 thick mahogany edge banding to. Later I’ll use a hand plane to bring the edge banding exactly to the surface of the MDF, and eventually glue the veneer on top of the edge banding, giving the illusion of solid wood.


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