What is a finger joint?
A finger joint is a glued joint used to join two pieces of timber end to end. In Dutch it is called a vingerlas. The end-grain faces are machined with wedge-shaped teeth or fingers that fit exactly into each other. They are then pressed together with adhesive under pressure. In this way long, straight pieces of timber are made from shorter parts.
Why a finger joint?
- Length: you make pieces longer than the tree or the sawn section allows.
- Quality: knots, splits and other weak spots can be cut out. The good pieces are then joined together again.
- Less waste: short offcuts remain usable.
- Dimensional stability: in combination with laminating, the timber warps less than solid timber.
Because of the large glue area of the sloping fingers, a well-made finger joint is strong, including in tension and bending.
Application
- Glued laminated timber (glulam beams): the laminations often consist of finger-jointed pieces. The requirements of EN 14080 apply to structural glued laminated timber.
- Joinery timber and mouldings: laminated and finger-jointed joinery timber is dimensionally stable and is widely used in joinery workshops.
- Structural solid timber (such as KVH): finger-jointed to long lengths. The requirements for this are set out in EN 15497.
- Skirting boards, mouldings and pine boards from the DIY store: here you can often clearly see the finger joints as a zigzag line.
Tips
- Painting: finger-jointed timber for exterior use often contains laminations with colour differences. Choose an opaque paint, or for staining choose timber without visible joints.
- Exterior use: make sure the adhesive is suitable for exterior applications. Laminated joinery timber for exterior use is made with weather-resistant adhesive; cheap interior timber is not.
- Making them yourself: with a finger joint cutter on a router table you can make finger joints yourself. The fingers must fit accurately and the adhesive must cure under pressure. Do not use home-made finger joints for load-bearing structures.
- Look out for open joints during inspection: a visible gap in the joint indicates poor gluing or too high a moisture content during production.
Related terms
- Glued laminated timber
- Timber joints
- Adhesive
- Lap joint
- Notched joint
- Window or door frame
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