Veneering a Bay Window in Place

Advice on applying veneer to architectural window trim on site. August 22, 2014

Question (WOODWEB Member) :
A client asked me to veneer the plywood around a bay window. The window is in a prefab 3/4" plywood box with an oak veneer on top currently. The veneer is stripped of finish and in good condition. The client is doing the room in maple trim and doesn't want the dark oak to show against the light maple.

1. There is no way to put a backer veneer on but I don't expect the substrate would flex because it's in place tied to framing. Agree?

2. Bay protrudes out 14" and is 96"wide with 30degree angles on side windows. I'm using a wood backed maple veneer. What's the best glue to use given the sun will be shining in everyday in southern CA?

3. Any other suggestions for securing veneer than two sheets of MDF with heavy weights for bottom section? For the top (ceiling) of box I was considering using the upper and lower potions of the bay and force fitting 2x4's for pressure but not sure if there is support further out toward the window and may separate the casing.

4. I usually use a straight poly finish but given the exposure, what about marine grade poly for longer life (no experience)? It seemed like an easy task at first. All straight flat areas, but with it being installed, it adds a level of difficulty. Thanks for the input.

Forum Responses
(Veneer Forum)
From Contributor K:
Since this is an installed piece there are a few challenges to overcome.

1. Even though you did not mention it, try to stay away from contact cement. Even if you do everything right in the application process. The direct sunlight and temperature increase will more than likely make soften the glue and allow it to creep. This has a very high potential for cracking your finish. Also, over time the glue tends to crystallize and deteriorate especially when exposed to UV.

2. Your way of applying pressure to the veneer once it is glued will not work very well. You might have some problems with bubbles later on in the places that did not get enough pressure. This might not become visible until the veneer had an opportunity to absorb and release moisture.

3. Maple veneer is notorious for moving even if it's backed. Of course you are using wood backed maple so that will help but still be prepared for that veneer to move some.

Things you might be able to do.

1. You could lay up the veneer on a substrate and then install the panel(s) over the exiting surfaces. In fact you might use 1/2 (or even thinner) maple faced plywood. It is already laid up!

2. You could use the old yellow glue and iron method. With a wood backed veneer this is a little more challenging because the wood backer sucks up glue and the extra thickness inhibits heat from transferring. Too much heat might check the maple face. I would recommend a lot of practice if you choose this option. Also this method works better with 10 mil veneer.

3. You could use PSA veneer. The installation process is meticulous but if done right can be successful. The problem area would be the inside top of the window. It is a lot tougher to exert enough pressure while working overhead but it can be done.

From contributor J:
I'd also highly recommend cladding the existing with some 1/4 maple ply. Your new maple casing can then be applied to cover the edge of the plywood, or you could edgeband it in solid if you need a little setback. If you don't like that, hot hide glue and a veneer hammer will do the trick.

From the original questioner:
Thank you both. The 1/4" maple ply sounds like the best idea. Since I don't have the experience in veneers the ply is forgiving because if I error on the cut it's an easy redo. You would both recommend yellow glue for securing long term or some other construction adhesive? What about pressure or nails while the adhesive dries between the ply and substrate? Or 1" brad nails puttied before final finish?

From contributor J:
I'd think you could use silicone, PL or liquid nails, in addition to some pins. By rights you should finish the backside before you attach it.

From the original questioner:
Silicone I trust. Liquid nails I've seen become brittle and loose hold. Also, I didn't understand your last comment about finishing the back side. Do you mean polyurethane the back side of the panel? That means the substrate would need to be done also as it's stripped to bare wood currently. Is this what you mean? If so, two coats of poly or should I sand an do a third coat for a smoother finished surface to increase adhesion?

From contributor J:
I would just give the back side of the maple a couple quick coats. I wouldn't bother trying to get it too smooth. I'd leave the oak bare for better adhesion, but silicone sticks to about anything so I wouldn't worry too much.