Glue joint strength comparator
"Is a dovetail really stronger than a butt joint?" — yes, by an order of magnitude in tension, less so in shear. This table ranks 14 common joints across two force directions and gives you the right adhesive for each.
Strength comparison
Why direction matters
A glued joint fails where the glue or the wood is weakest. In shear, the glue line is loaded — most modern wood glues are stronger than the wood itself, so failure is in the wood. In tension, the joint geometry matters more: a dovetail has mechanical interlock that resists being pulled apart; a butt joint relies entirely on glue adhesion to end grain.
Numbers are relative
The bars are normalised so the strongest joint for each direction is 100%. Real load capacity depends on:
- Adhesive type — polyurethane and Type III PVA are stronger than standard PVA in most situations.
- Surface prep — tight-fitting joints transfer load better than gappy ones.
- Wood species — softwoods fail at the wood, hardwoods can fail at the glue if the joint is starved.
- Clamp pressure — too little leaves a starved joint; too much squeezes out all the glue.
Limitations
- Numbers are relative, not engineering values. For structural calculations, consult an engineer.
- Doesn't predict fatigue / cyclic loading.
- Doesn't model impact resistance (a separate, lower number).
- Doesn't account for grain orientation across the joint — end-grain-to-long-grain is much weaker than long-to-long.
Frequently asked questions
Are dovetails really the strongest?
In tension, yes — by a wide margin. In shear, a well-glued mortise and tenon is comparable. In racking, multiple dovetails around a box beat any single joint. The right answer is "dovetails are the most forgiving of imperfect glue or wood, not necessarily the strongest on paper."
Is hide glue really weaker than PVA?
Modern hide glue is comparable to PVA in dry conditions. Hot hide glue has lower initial tack and is more sensitive to glue thickness; in restoration work that's a feature (you can heat the joint and disassemble), but for new construction, PVA is more forgiving.
Why does my chair joint keep loosening?
Chairs are racking-loaded — twisting forces that pull joints apart in tension. Most chair failures aren't glue failures; the wood around the joint has fatigued from repeated racking. The fix isn't a stronger glue; it's a joint geometry that resists racking (multiple dowels, wedged through-tenons, draw-bore).