“George, I’m trying to repair an old chair that needs some type of filler to save the end of the tenon. I don’t think regular wood filler would hold up. They are not completely bad, but have some chips and splits. If you have a suggestion I would be thankful.”
I’m throwing this one to our antique and repair expert, Dave Munkittrick.
WWGOA Contributing Editor Response:
This is a common problem in chair repair. You are right not to trust wood filler in this situation. Wood filler lacks the structural strength you need for a strong joint. A tenon’s strength is both mechanical and chemical. The mechanical part comes from a good fit between the tenon and the mortise so that the tenon is held firm by the mortise without the benefit of glue. The chemical part comes from the glue itself and for maximum strength, you want as much wood-to-wood contact as possible between the mortise and the tenon where the glue can bond. In both cases, missing pieces of a tenon will weaken the joint. Your goal is to restore the tenon to its original shape.
The best practice is to replace the missing pieces on the tenon with real wood, preferably of the same species. From your question I surmise that your tenon is not broken, but has some splits and missing pieces. For a small split in the tenon, it may be possible to glue and clamp the split back together. For a larger split that can’t be squeezed tight without deforming the tenon I take a sharp chisel and widen the split a bit to make a narrow “V”. Then glue in a wedge that’s slightly thicker and longer than the “V” cut in the tenon. The wedge should have a snug fit, but you don’t want to drive the wedge into the tenon. That might widen the tenon so it no longer fits the mortise. After the glue has dried, pare the wedge flush to the tenon.
If the corner of the tenon is broken or missing, cut off the missing corner at a 45-degree angle. Cut an oversize replacement corner and make sure the grain is running in the same direction as the grain on the tenon. Epoxy this piece onto the corner and trim it flush to the existing tenon.
You can get away with a few small chips on the tenon. For large chips I use a narrow chisel to gouge a ramp or channel in the tenon, then glue in a piece of wood to fit the channel and pare flush.
One more thing: you should use hide glue in your repair. If the chair is an antique, that is the glue that was used when the chair was made. Old hide glue is reversible and gets re-amalgamated by adding water. That’s the beauty of hide glue. If you use yellow glue, it will not be able to soak into the wood fibers as they will be sealed by the old hide glue. The resulting repair will not last.
I am currently working on an article on chair repair for the Guild, so stay tuned to this channel.
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