Furniture that arrives at a repair café often looks worse than it is — or better. The gap between appearance and structural reality is where a systematic joinery check earns its time. This guide covers the inspection sequence used by volunteer coordinators at several Canadian repair cafés, including groups operating under the Repair Café International network.

Woodworking hand tools on timber planks

Why joint type matters before you reach for glue

Different joinery systems fail for different reasons, and the repair approach follows directly from the failure mode. A mortise-and-tenon that has dried out and shrunk apart calls for a different fix than a dowel joint that sheared under lateral force. Applying wood glue without first identifying which case applies is a common source of repeat failures.

The three joint types most commonly encountered at Canadian repair events are:

  • Mortise-and-tenon — common in dining chairs and frame-and-panel construction from the mid-20th century onward
  • Dowel joints — widespread in flat-pack and factory furniture produced from the 1960s onward
  • Biscuit joints — found in tabletops, cabinet frames, and assembled panel goods from the 1980s

Step 1: Visual inspection without disassembly

Before touching the piece, observe it from all four sides and from above. Look for:

  • Gaps at joint lines wider than a business card (roughly 0.5 mm)
  • Diagonal racking — where a rectangular frame has shifted to a parallelogram
  • Finish cracking along grain lines adjacent to joints, which indicates historic movement
  • Old glue squeeze-out that has discoloured or crystallised, suggesting a previous repair attempt
A piece that racks more than 10–15 mm out of square typically has multiple failed joints, not just one. Repairing a single joint without addressing the others produces a stiff point in a flexible frame, which accelerates failure elsewhere.

Step 2: Manual stress testing

With the owner's permission, apply gentle controlled pressure to each structural joint by hand. The goal is to feel — not create — movement. For chairs, place one hand on the seat and one on a leg and apply alternating push-pull along the leg axis. For table frames, grip opposite corners and apply a twisting force.

Record which joints move and approximately how much. A joint that moves under hand pressure but snaps back cleanly has lost adhesion but the mechanical fit is intact — a good candidate for re-gluing. A joint that moves and stays moved, or that makes a grinding sound, may have a broken tenon or split component requiring wood repair before adhesion.

Step 3: Identifying the joinery type

Mortise-and-tenon identification

Partially disassemble where joints are already loose. Insert a thin palette knife or feeler gauge into the gap. A mortise-and-tenon will show a rectangular tongue of wood entering a matched slot. The tenon shoulder — the flat transition between the full component width and the reduced tenon — is usually visible as a step.

Dowel identification

Dowel joints are identified by the absence of a tenon shoulder and the presence of cylindrical holes aligned across the joint face. In factory furniture, dowels are often 8 mm or 10 mm diameter and spaced at regular intervals. A broken dowel that has sheared flush with the surface requires drilling and extraction — a process detailed in furniture conservation references such as those published by the Canadian Conservation Institute.

Biscuit identification

Biscuits (compressed oval wafers of wood) are not visible from the outside of an intact joint. They become identifiable when a joint has opened: the slot cut in each mating face has a characteristic elongated oval profile, typically 4 mm wide and 15–20 mm long. A biscuit that has swollen or compressed unevenly may prevent proper re-closure of the joint.

Step 4: Assessing re-gluability

Carpentry hand tools for joinery work

A joint is a good candidate for re-gluing when:

  • The mechanical fit is snug after old glue is cleaned from both surfaces
  • No components are split or cracked through their cross-section
  • The joint can be fully closed under clamp pressure without forcing

Old glue removal is essential. Most factory furniture from the post-war period used urea-formaldehyde or PVA adhesive. Neither bonds reliably to itself once cured. At community repair sessions, a combination of mechanical scraping with a chisel or palette knife and moisture softening (damp cloth held against the joint for 15–30 minutes) removes most historic adhesive without damaging the wood substrate.

Step 5: Documenting findings before repair

Repair café volunteers at the Canadian repair café network typically use a simple condition report noting which joints are failed, what type they are, and whether disassembly is needed. This takes under five minutes and prevents mid-repair discoveries that require stopping work and leaving a piece partially disassembled.

A workable shorthand for the condition report: note each joint by position (e.g. "front left chair leg, lower rail"), grade it Pass / Monitor / Repair, and note the joinery type identified. This document stays with the piece during the session.

Common mistakes at the inspection stage

  • Applying pressure to joints that have not yet been identified — this risks breaking a tenon that is intact but surrounded by a failed joint
  • Mistaking finish cracking for structural failure — surface lacquer often cracks along grain lines without any joint movement
  • Assuming all joints of the same type have the same condition — in a four-legged chair, two joints may be sound while two are failed
  • Overlooking the seat-to-frame connection in upholstered chairs, which is often a hidden joint system under fabric

Related: Veneer Patching Techniques → Tool List for Repair Cafés →