Canadian Woodworking

Advanced-level chair repair

Author: Scott Bennett
Photos: Scott Bennett
Published: February March 2023
Chair repair
Chair repair

If you have moderate woodworking skills, you have the necessary skills to repair broken furniture.

I’ve found repairing chairs rewarding and challenging work, and more enjoyable than designing and building custom furniture. I’ve also found it to be a more profitable busi­ness model. In my previous two articles, I described how to repair a chair with loose joints and how to repair broken furniture parts. This article builds on those skills and is what I call “Level 3 Woodworking Repair.” I’ll describe how to diagnose the situation, remake furniture parts and stain them to disguise the repair before reassembling everything.

Snapped Off
Many of the back slats and both of the main back posts were broken. Simply gluing them back together wouldn’t work, as end grain-to-end grain joints are inherently weak. The broken slats and posts needed to be removed, new ones made and finished before the chair could be reassembled.

Chair repair

Turn Other Posts
Using the existing post as a guide, Bennett turns two matching posts on his lathe. He machines the mortises while the blank is still square, then fills the mortise with a piece of scrap, held in place with a small amount of glue, while he turns. The mortise filler can be removed by driving a screw into the filler and pulling it out when the turning is complete.

Chair repair

Black Paint Darkens the Pores
In order to match the finish on this chair, Bennett wiped on black acrylic paint, then sanded it off. The result is darker pores.

Chair repair

Round Tops
Bennett uses his shave horse to hold the posts while he rounds over the tops of the posts.

Chair repair

Different Stages
Here are the different stages of the posts as they get completed, from left to right: a rough blank; a partially turned post; the turned post with black paint; the paint mostly sanded off; and the post ready for final assembly.

Chair repair

Simple Finishing Jig
A simple jig to hold the parts while finishing is easy to make.

Chair repair

Make Some Wedges
A wedge helps secure the through tenons on the end of the posts. It’s driven into the end grain of the posts once they’re seated properly in the mortises.

Chair repair

Tap It In
Oriented perpendicular to the grain as to not split the solid wood seat apart, the wedge is tapped into the slot on the end of the post. Glue will help keep the joint strong for years to come.

Chair repair

As Good As New
The completed chair, with all its newly made and finished parts reassembled into a solid seat for the customer.

Chair repair

Diagnose the problems

Every repair starts with the same step: determining the root cause of the problem so you can correct it. This chair was previously repaired, but the repair failed. As these parts have broken across the grain, there would be no strength if they were glued together again.

To restore this chair to a working piece of furniture, I needed to make new parts to replace the broken ones. This chair was part of a set of four I was repairing.

Duplicate parts

To reduce how noticeable the repair would be, I decided to spread the repair across two chairs. I made slats for a chair where all the other parts were in good shape. I took a few slats from that chair and used them on the chair with the broken back posts. Having said that, you don’t need multiple chairs to make a solid repair that will be undetected.

I started by making the new back posts. After selecting some straight-grain oak, I mortised slots in the blank to fit the crest rail. I then added a dab of glue on some sacrificial tenons and inserted them in the mortises to prevent tear-out when I turned them on the lathe.

Once the turnings were complete, I started the finishing process while the back posts could still be mounted on the lathe. The first step in my process to mimic vintage oak is to paint the parts with black acrylic paint and then sand off the surface. I’ll share more of these finishing details later.
After I cut off the top of the back posts, I moved over to the shave horse I designed for my workbench. It’s a compact holding tool that allows me to use my foot to apply clamping pressure while I use both hands to use the spokeshave and drawknife. I duplicated the dome shape from the broken back posts and applied a coat of paint for the finishing process.

I used the benchtop shave horse again to recreate the back slats. I found this to be a relaxing task, using hand tools to quietly shape the oak slats. It made me wonder what the original craftsman who made this chair was like. Did they work fast and furious or pur­poseful and efficient? Did they have decades of experience or was it an apprentice knocking out these parts?

As I made each part, I test fit it to ensure the connection was snug without needing to force the joinery together. This ensures I will have a smooth process when I’m gluing up the chair because all the pieces will come together well at that critical point in time.

Matching stain and finish

One of the more challenging skills for me to learn when repairing furniture was how to match the stain and finish. I learned how to use acrylic stains from a furniture finishing mentor who taught me how to “set the grain” first, then apply the stain. I use black acrylic paint – the kind found in a craft store – to set the grain. After sand­ing the surface of the oak, the open pores retain the black paint.

The next step is to apply the acrylic stain. I use Saman stain, which is made in Quebec. I love this new generation of stain because I’m not exposing myself to harsh chemicals in my workshop and it washes up with soap and water. I was able to colour-match the new parts with the other chairs in this set.

I find the stain changes colour as it dries, but not in a bad way. When it’s wet, it looks like it will after a clear coat is applied. This is helpful as it allows me to dial in the colour I’m mixing using various stains.

This chair was originally finished with polyurethane, so I applied several coats of polyurethane to the new parts. This brings up the colour of the dried stain and gives the parts the same level of sheen as the rest of the chair.

Reassemble

The last stage was putting it all back together again. This is where some knowledge of chair making is important. The chair back posts are held in place with “wedged through mortises.” As you can see in the photo of the old back post I pulled out, there is a slot cut in the tenon. The chair post is held in place by inserting the tenon in the mortise (hole) that goes through the seat, then driving a wedge into the slot. This expands the tenon and applies pressure that prevents the tenon from pulling out.
For a wedged tenon to work properly, the wedge can’t be parallel to the grain in the chair seat or it would risk splitting the wood. The wedge needs to be located perpendicular to the grain in the seat so the pressure is applied to the end grain.

I used a dovetail saw to cut a slot in the tenon. To make the wedges I used a simple jig I made that holds a small piece of wood in place on an angle. This allows me to plane it down to create the right size wedge.

The last step before the glue-up is to test-assemble all the parts to ensure they fit properly. I then applied hide glue to both the mor­tises and tenons with an artist brush and connected all the joinery. I then flipped the chair upside down so I had access to the split tenons in the back posts. I added a clamp to hold the back tight to the seat. I then added glue to one side of the wedge and taped it in while holding the post with my hand to ensure I didn’t knock the post out of the mortise in the seat.

The finished repair

The reward for completing a project like this is a sense of accom­plishment and pride. The added bonus is seeing the reaction of my customer when their furniture is rock solid and beautiful again.

Scott shares his skills on his “Fixing Furniture” YouTube channel. You can watch this repair project and 75 other videos to learn about furniture restoration or visit his website at WoodenItBeNice.ca


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