Joinery Choices: Knowing When to Reinforce Your Glue-Ups
In woodworking, few topics generate more questions from beginners and seasoned makers alike than this: Should I use biscuits, dominoes, or nothing at all when gluing panels? While there's no one-size-fits-all answer, there are clear situations where reinforcement can make or break your project — and others where it may just be unnecessary extra work.
Whether you're building tabletops or cabinet panels, knowing when and how to use biscuits or dominoes (and when not to) will save you time, frustration, and sanding discs. Let’s break it down into two key decision points: joint strength and alignment control.
Bad Glue Joints: When Adhesive Alone Isn’t Enough
The first major reason to use biscuits or dominoes is when your glue joint may be compromised. Not all timber species take glue equally well — especially some of Australia's denser, oilier hardwoods like blackbutt, spotted gum, and ironbark. These timbers can resist PVA glue, weakening your bond. In such cases, a mechanical joint — such as a biscuit or domino — adds critical reinforcement.
You can improve glue adhesion by wiping the glue edges with acetone just before gluing. This removes surface oils and improves the effectiveness of the bond — a simple but effective prep step.
There are a few other scenarios where the glue joint might be weak:
- End grain joints – Glue has little holding strength here, so biscuits or dominoes become essential for reinforcement.
- Plywood edges – The layered structure includes a mix of long grain and end grain, and not all layers align. Adding mechanical reinforcement improves both strength and reliability.
- Rough or torn-out jointing surfaces – Whether your boards are too long to joint properly, you're missing the right tools, or you've got tear-out from the planer, any imperfection in the glue face can compromise the bond. Biscuits or dominoes help bridge the gap — literally.
If you’re ever in doubt about the integrity of your glue joint, adding a mechanical connector is usually the safer bet.
Fixing Alignment: Preventing Gaps and High Spots in Panels
The second key reason to reach for biscuits or dominoes is board alignment. Even when the glue bond is strong, twisted or warped boards can make glue-ups difficult. Biscuits and dominoes help align edges during clamping, reducing high spots and saving hours of sanding.
For long panels — especially those made of wide boards — even a slight twist or bow can lead to visible seams. In these situations, reinforcement doesn’t just add strength — it simplifies the glue-up process. If you're working alone, mechanical alignment aids like dominoes give you valuable setup time and help keep everything square while you clamp.
Clamping cauls can help flatten panels across the width, but they don’t offer the edge-to-edge alignment biscuits and dominoes provide.
Why does this matter? If your only method of flattening a panel is sanding, even a small misalignment between boards can burn through sandpaper — particularly with hard species like blackbutt or blackwood. Sanding out a half-millimetre discrepancy can be both slow and damaging.
And while a thicknesser can make quick work of uneven joints, that’s not always an option. Panels may already be too thin, or simply too wide for your machine. In these cases, getting the alignment right during glue-up is critical — and that’s where dominoes and biscuits shine.
When You Can Skip Them: Saving Time Without Sacrificing Quality
Despite their advantages, biscuits and dominoes aren’t always necessary. If your boards are:
- Already well-jointed with a tight glue face
- Made from a glue-friendly species
- Going through a thicknesser after glue-up
- Cut from thicker stock (30–40mm+)
...then glue alone may be perfectly sufficient. In these cases, the extra time spent cutting joinery can be saved and repurposed elsewhere in the build. Reinforcement should serve a purpose — not just be done out of habit.
Tool Options: Domino, Biscuit Joiner or Router Slot Cutter
If you have access to a Festool Domino, it offers more strength and versatility than a biscuit joiner. But biscuit joiners are far more affordable, and still provide excellent alignment and moderate strength.
No biscuit joiner? A slot cutter in a router or router table can achieve the same result. Just make sure the cutter matches the thickness of your biscuits — around 4mm is standard. Be careful with placement: if the biscuit slot is too close to the surface, especially in softer materials like MDF, the expanding biscuit can leave a visible bulge.
Pro Tips for Efficient, Clean Glue-Ups
- Mark everything clearly before cutting your slots — A, B, C, etc.
- Dry fit the full panel before applying glue.
- Use acetone to clean oily timber surfaces right before gluing.
- Apply glue in the narrow holes only for dominoes, and on one glue face — this gives you more time and less mess.
- Add clamping cauls above and below to keep the panel flat as you apply pressure.
- Don’t overdo it with water during glue clean-up — especially on thin panels, which can warp from uneven moisture.
Whether you're building a desk, a dining table, or a door panel, understanding when and why to use biscuits or dominoes will improve your builds and streamline your workflow. It’s not about always using more — it’s about using the right technique at the right time.