Intermediate-level chair repair
I described how to repair a chair with loose joints in the October/November issue. This article builds on those skills and is what I call Intermediate-Level Woodworking Repair. Here, I’ll cover how to glue broken parts together so you can reassemble the chair and get it back in working order.
The most important element for repairing broken furniture is glue. Different types of glue have advantages and disadvantages, so you need to understand how to use them properly to ensure your repair doesn’t fail.
The broken chair back pictured here required three types of glue to bring it back to life.
A Perfect Match
The smaller piece that has broken off fits back in place nicely, without any gaps. Because of this, PVA glue can be used to glue the broken piece in place again before moving onto the other parts.
Squeeze It In
If a part splits but it hasn’t broken apart, Bennett uses a syringe to squeeze glue into the split before he applies some pressure to close the split and continue with the repair.
Bennett will use epoxy if the joint has gaps and doesn’t mate nicely. A small brush to apply the epoxy goes a long way to ensuring things are tidy and the epoxy ends up where you want it.
Don’t Over Clamp It
When working with epoxy you don’t need a lot of clamping pressure. Epoxy works best when it has at least a bit of thickness to it. Here, Bennett applies light pressure to bring the joint close together, then removes the excess epoxy before it dries.
Scrape It Smooth
Whether you’re using PVA or hide glue, ensure the surfaces mate properly. Scraping the joint is important to remove the old adhesive, finish, or even dirt.
Bennett inserts the bit into the dowel hole with the drill on reverse, then switches it to forward to remove the old adhesive. This way there’s a lot less chance of drilling the holes larger or on an angle.
Give It Time
Once all the parts have been glued back together and the clamps have been applied, let the adhesives dry thoroughly.
The Right Direction
Pressure needs to be applied with clamps perpendicular to the glue line in order to get a strong joint. This means many clamps may have to be used in certain instances.
Like New Again
After all the cleaning, prepping, gluing and clamping you’ll have a great chair to enjoy.
The most common glue used in woodworking is polyvinyl acetate (PVA). It’s a water-based glue that excels at adhering wood fibres together. In fact, it works so well that a properly glued seam between two pieces of wood is stronger than the wood fibres in the wood. It’s an excellent glue when used the right way.
For PVA glue to work properly, four requirements need to be met:
For repairing parts that have broken off, and if you have all the pieces, this is a good application for PVA glue. If there are gaps, PVA won’t work.
I apply glue to both sides of the broken parts using an artist brush. This ensures there’s enough glue in all the crevices to make the strongest possible bond. When the parts are clamped up, glue should squeeze out of the edge. If you don’t have glue squeezing out, you don’t have enough glue to ensure a strong bond.
Another place to use PVA glue is in splits. Using a blunt-tip syringe, I inject the glue deep into the split. After clamping, simply wipe off the excess glue with a damp shop towel.
If the broken part doesn’t fit together 100%, then PVA glue can’t be used. On this chair, the back slats that broke had been previously repaired by someone using PVA glue. After scraping off the old glue, the parts didn’t fit well. This is where epoxy has an advantage over other types of glue. Epoxy will hold when there’s a gap between the parts.
As you may know, epoxy is a two-part adhesive. By mixing up the resin and the hardener, a chemical reaction begins which cures the adhesive. Read the directions carefully to understand how long it will take to get to full strength. I begin this type of glue-up by testing my clamping setup to make sure I have everything ready.
I mix up the epoxy in a silicone cup to allow me to reuse the cup and avoid disposable waste. A silicone stir stick doubles as an applicator. I then align the parts and apply light clamping pressure. If you apply too much clamping pressure, you could squeeze out too much adhesive and not have a strong bond.
It’s important to wipe up the epoxy squeeze-out immediately before it dries. To be safe, wear gloves and a respirator with organic cartridges to protect yourself from these strong chemicals.
While PVA glue makes a permanent bond, it’s not good for furniture joints when working on antiques. Hide glue has the unique property of being reversible, meaning you can “unglue” a joint. This is important when working on antiques so they can be disassembled in the future if a part breaks.
Like PVA, hide glue needs tight joints, clean surfaces, enough glue applied and clamping pressure. I clean off the joints with a paint scraper and file. For the round mortises, I use a drill bit to clean out any old glue. The trick is to run the drill backwards to get the drill bit to the bottom of the mortise first, then switch it to forward and run it to clean out the glue residue. This technique ensures the mortise doesn’t change direction when drilling.
When applying the glue, I use an artist brush. The back end of the brush handle works well to line the walls of the mortises with glue. I use the brush end for the rest of the parts. When all the parts of the chair back are together again, I clamp it up and let the glue dry.
Hide glue is also water soluble, so I use warm water and soap to clean the artist brush for the next project.
As I mentioned above, clamping pressure is an important part of using glue effectively. I prefer to use trigger clamps as the built-in rubber padding helps grip parts that are on slight angles or curves. I add enough clamps to provide pressure along the whole seam while holding the aligned parts in the right position.
Sometimes the curves on the piece don’t provide a surface for clamping. This is where “vector clamping” comes in. It’s a process of making clamping cauls that allow the clamps to provide pressure 90° to the joint. Creating the cauls requires tracing the shape of the part to be clamped on scrap lumber and cutting it out. Next, determine where you want your clamps to be located and notch out locations for the clamp pads to sit parallel to the seam. In many cases, you’ll also need to notch locations for additional clamps to hold the caul in place.
At this stage you can combine what you know about selecting and using adhesives to repair chair parts and combine that with the basics on how to re-assemble a chair to tackle many different chair repair projects.
As you can see, this chair is back in working order, thanks to a selection of glues. However, this process won’t work in all situations where there are broken parts in furniture. Sometimes the parts can’t be glued back together again. In the next article, I’ll show techniques for successfully making replacement parts for broken furniture using Level 3 Woodworking Repair skills.
To watch how this repair is completed in Scott’s workshop, visit his “Fixing Furniture” YouTube channel. There are 75+ videos on his channel, including how to create cauls for vector clamping.