What is a butt joint?
A butt joint is the simplest connection there is: two pieces of timber, or two bars, simply meet end to end with their cut ends butted tight together. There is no tongue and groove, no lap and no housing. The Dutch word stuik means the sawn end of a board that has to meet another, and also the joint itself; the verb stuiken means to butt. In metalwork, joining two plates, bars or pipes in line is a butt weld, for example a single-V butt weld.
A butt joint is quick to make but transfers almost no load on its own. Its strength comes from what is underneath, which is why it is used for scaffold boards, floorboards and cladding laid over supports.
Application
- Land every joint on a joist or batten. With floorboards, boards and cladding, each butt joint must sit on a support so both ends can be fixed.
- Stagger the joints. Do not let neighbouring boards butt on the same joist. Staggered joints give a stiffer floor and a neater look.
- Cut square and clean. A ragged or out-of-square end leaves an open joint. Use a mitre saw or a square and remove the burr.
- Protect the end grain. End grain soaks up the most moisture. Outdoors, give cut ends an extra coat of primer or end-grain sealer and leave a small gap so water can drain.
- Support sheet joints. With boarding or sheet flooring, put a batten or noggin under every butt joint, otherwise the joint flexes and the finish cracks.
- Prepare butt welds in thicker material. On thicker plate or pipe the edges are usually bevelled (a V preparation) so the weld penetrates the full thickness.
Common mistake: leaving a floorboard joint floating between two joists. The loose end bounces, creaks and eventually lifts.
Related terms
- Tongue and groove
- Joint
- Scaffold wood
- Welding
- Batten
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