Finger Joint Telegraphing

Given time, finger joints in lumber will show up through almost any finish. November 12, 2006

We plan to use finger joint timber for making picture frame mouldings. Gesso is applied on the raw FJ wood to fully cover them. They are then sanded, and spray painted. We were told that some 3 to 4 months later, images of finger jointing can be seen - this is considered a defect in our industry. These images cannot be seen at the time of production. Has anyone encountered this problem?

Forum Responses
(Finishing Forum)
From contributor C:
The finger joints in moldings and lumber tend to telegraph through the painted finish upon changes in moisture content, because of the wood shrinking and swelling. If you used this in a museum, for instance, with constant humidity control, there would likely be no showing of the finger joints, since it will not shrink or swell.

From contributor J:
You don't say what kind of paint you are using. That could make a difference. Also, I would try using a primer like Zinser under the paint.

From contributor R:
Unless you cover those joints up with something like a canvas or a sizing, they will always come back to say hello. Might take a few months or even a fewer months, but count on them to return. That's the nature of a joint, and especially a finger joint, which is a whole bunch of joints in a small, confined area.

From contributor V:
This will continue to be a problem no matter what coating you put on. The real solution is to use a better (solid wood) molding as your base. For architectural grade work, where the pieces are mostly viewed as background at a distance, the FJ is okay (though on high end jobs I usually avoid it). For picture moldings, it is pretty tacky and would serve only the lowest end of the market.