GLUING STRATEGIES AND TECHNIQUES
For many woodworkers, glue-up and assembly can be unnecessarily stressful. There are several reasons for this. First, time is not on the gluer’s side. Common yellow glue has approximately 5 minutes of open assembly time, leaving little leeway to think and act once the glue is wiped on. Next, glue-up is often irreversible. There are some exceptions, but for the most part it’s a one-shot deal. Additionally, freshly applied glue is slippery and joints and parts can easily slide out of alignment. Furthermore, when glue squeeze-out cures, it can be difficult to remove. And when cured squeeze-out goes undetected, it’s a potential finish wrecker. Finally, because wood never stops moving, improper glue placement that doesn’t allow for seasonal wood movement is an invitation for cracks and splits to happen.
It’s important to have a glue-up strategy. I begin with dry fitting. I lay down all the project parts in their proper order and visualize where the glue will go and what clamping tools and accessories I will need.
Label the workpieces and gather the tools and supplies for dry-fitting.
After labelling the parts (using lines or numbers) in their proper orientation, I decide if the assembly should be glued in small sections (subassemblies) first. I proceed with a dry clamping to identify any problem areas or tool shortages.
Gather Your Glue Supplies
For general woodworking purposes, PVA glue is the common choice. There are two ways to gain open time to work on the assembly. The first is to use a product that sets slowly. Hide glue, white glue and 2002 GF glue are some examples. Each leaves an open time of approximately 15 minutes. Alternatively, you can extend the glue’s open time by diluting it according to the manufacturer’s guidelines. For example, if you thin Titebond yellow glue by 5% (1 part of water to 20 parts of glue), you'll have about 50% more open time.
In terms of applicators, there’s an array of choices that includes brushes, the tip of the glue bottle, finishing nails, cotton swabs, credit cards, paint rollers, toothbrushes, your finger, etc.
Be creative with what you can use as a glue applicator.
Gluing is a messy job, so I keep a bucket of water and some rags handy. I also installed a retractable vinyl window shade on my workbench to protect the work surface.
Protect your assembly table.
Dealing With Squeeze-Out
Too much glue is a waste and creates time-consuming clean-up work. That’s bad. Equally bad, however, is too little glue, which can result in a weak joint. A little squeeze-out on the joint line is a sign of proper coverage.
Glue is stronger than wood if applied properly.
The following are some before and after glue-up tips:
- Protect your surfaces, especially those that are difficult to clean.
Simply cover them with masking or cellophane tape. Another less-used method is to pre-finish the mating parts. (Care should be taken to keep finish off the surfaces to be glued.) Remove any squeeze-out and then apply your final coat of finish.
Dry fit the joint and tape along the inside edges.
- Keep excess glue inside the joint.
This strategy relies on creating a void into which the surplus glue can escape. It also relies on applying glue to the non-end-grain surfaces only. It works well for dado joints (with chamfered ends) and dowel joints (with deeper holes). Two examples are given below:
a) Mortise-and-Tenon Joints
Make a void by cutting a mortise about 1/16” deeper than the length of the tenon. Apply glue to the walls of the mortise only, not the shoulders or tenon cheeks.
Cut a deeper mortise and apply glue to the walls of the mortise only.
Cut a pair of grooves 1/8” deep near the back edges of a decorative piece to provide voids. Spread beads of glue between the grooves only.
Cut grooves to create voids for any squeeze-out.
- Remove squeeze-out wisely, either before or after it’s cured.
When removing wet glue, I avoid using a damp rag because it can smear the glue over a larger porous area. If the squeeze-out is on the inside joint edge, try scooping it up using a drinking straw.
I prefer to let the excess glue set for about 30 minutes until it’s in a rubbery state. I then remove it using a sharp edge such as a chisel or a putty knife. For cured squeeze-out, I use a scraper (card, cabinet, or paint scraper). To minimize tear-out, remove the hardened glue within about eight hours after applying it.
Scrape off the glue squeeze-out using a card or cabinet or paint scraper.
If squeeze-out can’t be avoided, try setting up the joint so that the squeeze-out occurs on the outside surfaces. This will work with rabbets, box joints, dados and dovetails. For example, when gluing up a dovetail joint, I apply adhesive to the sides of the tails only. When the tails are pressed into the dry pins, the surplus glue squeezes to the outside surfaces, which is easier to remove. In the case of box joints, apply glue to one piece only.
Apply glue to the sides of the tails only. Leave the pins dry.
Keep the squeeze-out to the outside surfaces.
Mind the Wood Movement
Using a solid-wood frame-and-panel construction as an example, the narrow rails and stiles that form the frame can be glued together at their joints. Not gluing the wide panel into the grooves means that seasonal movement across the panel’s width is not hindered.
Plan for differential wood movement to avoid cracking and splitting.
To keep an even reveal on the panel, put a dab of glue in the center of the top and bottom edges. Or, better yet, use spacers (e.g. panel barrels) in the grooves to keep the panel centered.
Charles Mak, now in retirement, is an enthusiastic hobby woodworker, teacher, writer and tipster. He formerly worked part-time at his local Lee Valley Tools store.