What is a mitre joint?

A mitre joint is a joint in which two parts are cut at an angle, so that the cut faces meet and the parts together form a corner. For a right angle of 90 degrees, you cut both parts at 45 degrees. The advantage: no end grain is visible, and a profile runs neatly around the corner. In Dutch it is called verstek; in American English the spelling is miter.

Where do you use a mitre?

• Skirting boards, ceiling mouldings and cover strips
• Door and window trims (architraves)
• Picture frames
• Frames and corners of furniture and cabinets
• Tiling and natural stone on external corners (mitred by grinding or sawing)

Tools

• Mitre box: a trough-shaped box with saw slots at 45 and 90 degrees, for narrow mouldings with a handsaw.
• Mitre saw or chop saw: an electric saw with a rotating table on which you set any angle accurately.
• Mitre square: a square for marking lines at 45 degrees.
• Sliding bevel: an adjustable square for copying any angle.

Step-by-step plan for a tight mitre

1. Measure the real angle: walls are rarely exactly square. Take the angle with a sliding bevel or angle finder and divide it by two.
2. Cut a test piece from an offcut and check whether the corner closes.
3. Measure along the long side of the mitre, and allow for the saw kerf.
4. Glue and reinforce: a mitre has little gluing surface, because you are partly gluing into end grain. Reinforce the joint with a dowel, biscuit, spline or timber peg. For mouldings, you can also use mitre clamps or a strap clamp.
5. Fill and sand once dry, and finish with varnish, paint or stain.

Common mistakes

• Moulding the wrong way round in the mitre box: you cut a ceiling moulding upside down and against the fence, the way it sits against the wall and ceiling.
• Cutting an internal corner as a mitre on a profiled moulding: on an internal corner that is not square, a mitre often closes poorly. A coped joint, where you cut out the profile, then gives a neater seam.
• Timber shrinks: with wide mitres in solid wood, shrinkage can open a gap on the inside. Use well-seasoned timber.

Related terms

• Wood joints
• Mitre saw
• Skirting board
• Mouldings
• Dowel

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