All conditions
Condition
Flexing or movement
The joint bends, flexes, or the materials move against each other (e.g. wood with humidity).
What to do
Working with it
- A joint that moves needs an adhesive that moves with it. Rigid glue on a flexing part is the single most common repair failure.
- Wood moves with humidity even when nothing bends it, so a wide panel glued rigidly across the grain will split itself.
- Silicone, polyurethane, and rubber-toughened super glues all tolerate movement; plain epoxy and plain CA do not.
Adhesives
What holds up, and what doesn’t
Better under this condition
Ruled out by it
Questions
Common questions
- Why does the same rigid repair keep cracking?
- The movement did not disappear when the crack was glued; it shifted to the edge of the new rigid patch. The repair needs either an adhesive that can move, a larger flexible transition, or a mechanical design that stops the bending.
- How do I glue wood without fighting seasonal movement?
- Let wide parts move across the grain instead of locking the whole width rigidly. Place the adhesive where the design can tolerate movement, or use joinery and fasteners that restrain one point while allowing the rest to slide.
- How can I tell whether an adhesive stays flexible?
- Look for the maker to describe the cured adhesive as flexible, elastic, or suitable for moving joints. A thick gel before curing can still become a brittle solid, so uncured texture tells you very little.
- Why do joints between different materials need movement tolerance?
- Different materials expand, contract, and bend by different amounts under the same conditions. A compliant glue line absorbs some of that mismatch instead of forcing all the stress into one sharp edge.