Expert: Jamie Yocono - 10/14/2009

Question
I am a construction manger and we are just finishing off a condo renovation on the ocean.  The kitchen cabinets have been finished in solid built up alder panels with the alder strips in the vertical direction.  The panels are finished in a polyurethane finish on all four sides and look beautiful.  We (Owner Included) expected the panels to move some with the change in humidity, however we are seeing 1/2" cupping over a 16" door.  We are now working towards a solution, but my question is as follows: Are there steps in the gluing up of the panels that can be taken to minimize this movement or is this type of movement typical in this style of panel?  Should we have opted for an alder veneer over a stable core over the glued up panels?

Thank you in advance,

Darren

Answer
Darren,

There is a method for gluing up solid wood panels that will minimize that cupping. It's not perfect, but it helps. If you look at the end grain of a board, you will see the annual growth ring of the tree. If you alternate the direction of those rings - so that one board's rings curl up, and the next one down, and so on, you will minimize that large amount of cupping across the whole panel of wood.

Now some woodworkers don't do this, as using this method will mean that you will possible have some sapwood in your finished piece. So many woodworkers simply glue up their panels for appearance, rather than controlling movement.  But I think controlling the cupping is the most important thing, more so than appearance. If I see sapwood when I'm making a solid wood panel, I try to either trim it out of a board, or use a different piece of wood.

Another way I control cupping is by housing the whole panel within a dado around the perimeter. That means if I'm building a door, that panel's edge is completely enclosed within a dado, making it difficult to cup. Of course, that doesn't work with a slab door like you have. This only works with a five piece door - two stiles, two rails, and a flat panel.

If you're not making  five piece door, you obviously can't house the panel in a dado.  :/ So another method is to use a cleat on the back side of the solid panel, so that the cleat keeps the panel flat. This method works well. But - if you use a cleat, you have to orient the grain of the wood in such a way that the cleat will stay flat.

Think of how a 2x8 is used on edge as a joist, so that it is stiffer than using it flat. If you're going to apply a cleat to the cupped slab door like yours, you need to pull (with a clamp) the door flat against the vertically applied cleat, then screw into it, and the cleat will help keep it flat. I would use two cleats per door, one probably three inches off the top, and the same distance off the bottom.

OK, I hope this helps. Feel free to write back if there was anything that you didn't understand, or if you have more questions. Good luck, too. Cupping doors are a real pain!

Jamie Yocono
Wood It Is! Custom Cabinetry
Las Vegas, NV
www.wooditis.com