Door Finishing and Wood Movement

Thoughts on how to prevent bare wood from being exposed when door panels and frames shrink during dry seasons. November 13, 2009

When building flat panel (solid wood) doors, must the panel be finished prior to assembly? These doors are cope and stick hard maple with 2 1/2" stiles and rails. Widest door is 24". Can't outsource, as customer is supplying birdseye boards to use for some of the panels.

Forum Responses
(Cabinetmaking Forum)
From contributor W:
I'm going to venture a guess that you are concerned about the panel shrinking and showing an unfinished edge. If the wood has a higher moisture content than should be, and you can't wait for it to dry completely, then finishing the panel first would be a good idea. If already at a good MC for your location, it probably won't shrink any further. Since it is birdseye, they might be willing to let you dry the wood out some, which would be the right thing to do anyway.

From contributor T:
I have to respectfully disagree with contributor W.

The wood will shrink and expand seasonally. It will shrink and expand whether or not it is finished, since the finish will just slow the moisture exchange between the air and the wood, not stop it. (That's why 5 piece doors are built, to accommodate seasonal wood movement.) Maple actually expands and contracts quite a bit, seasonally.

It won't hurt to finish the panels before assembly, but it does slow the door-making process. I'm not sure if it would help anything. What are you trying to avoid with pre-finishing the panels?

I'm getting a bad feeling from somewhere in my memory when you mention solid birdseye panels. You know, when a customer says "can we do it this way?" and you get a bad feeling, but you don't know why? Until you start fabrication, then the reason comes back. I think if a customer asked me to build birdseye panels I would use the AWI premium style for building them, not solid wood. I kind of remember experiencing some pretty wild movement with birdseye. I could be wrong, though.

From the original questioner:
Thanks for the replies. My concern is seeing an unfinished edge when the panel shrinks.

From contributor S:
I prefer to finish first when I can, then assemble. If you finish first you must use tape to protect the mortise and tenon from any finish to keep a good glue surface. It might take a bit longer, especially if it's out of sequence of your normal routine, but I wouldn't think much.

When I finish after assembly I use air to push the finish into the hard to reach areas. I've had good success using both methods. Either way, don't forget the space balls.

From contributor J:
I don't think birdseye moves any more than other maple, but you can't be sure how customer-supplied material was dried and stored. If he air dried it or stored it in a basement or garage, then its MC will be on the high side and the panels will shrink. If it's been stored in a hot attic or an air-conditioned space, then you may have no problem at all. Check the MC!

From Professor Gene Wengert, Sawing and Drying Forum technical advisor:
Curly or birds eye does not shrink as much as regular flatsawn, but they do move varying amounts here and there at times, meaning that some non-flat surfaces may result.

Contributor W has the correct idea, but your shop's conditions (EMC of the air) may be equal to the MC of the wood, so everything is happy, but the problem comes when the customer has drier conditions. Shrinkage will result. There is no finish that stops drying and shrinkage. Due to the difference in movement of the frame and the panel, it is not a good idea to glue the panel to the frame; rather use a floating panel and space balls, as indicated. Therefore, as the tenons (panel edges) will not be glued, I am not sure why you need to protect them when finishing.

From the orginal questioner:
What I'm worried about is, when the panel shrinks, will there be a visible line where there is no finish, because it was hidden when the finish was applied?

From contributor F:
Taking for granted that the wood is dried properly to begin with, a maker can take the seasons into consideration for making decisions. For instance, if you build the doors in say, late February, you can be fairly sure that the panels will be shrunk to the narrowest point in the cycle.

From contributor P:
I run a paint brush around the edges when I'm staining and push the stain down into the frame, no problems.

From contributor D:
I read all the very good advice from all that posted. But I think you're missing something. I can't see how a 24" wide birds eye maple panel isn't going to give you problems over time. It's your reputation that is going to take the hit. Talk them into veneered door panels - save the solid stuff for the rest of the cabinet. I can't believe the customer, or anyone else, could tell. If you wanted to outsource the doors, you might want to ask if your supplier would use your wood. Might save a ton of time. I bet they might, especially in this economy.

From contributor L:
We usually wipe stain or sealer on the edge of the raised tongue and then assemble. It is going to move, period. You can help disguise this by putting whatever - stain or clear - on the edge of the panel, and it does help.

I have built raised panel wet bars for exterior and painted them and just used this technique and not had a problem. I have made 48 wide panels raised over hearths and not had a problem. It all moves and some more than others. Period.