Chimney Breast Skirting External Mitre Uk

A chimney breast return is a high-visibility external skirting corner. Cut two 45 degree mitres only if the corner is truly 90 degrees. In older UK living rooms, measure the actual outside angle, bisect it for the two opposing cuts, then test on offcuts before cutting the full skirting length.

Why chimney breasts show every error

A small internal skirting flaw can hide in shadow. A chimney breast external sits proud in the room, often near a fireplace or alcove, so a bad mitre catches light from both sides. The left return and right return can also differ because plaster builds up around old openings.

MW Profiles' UK skirting guide explicitly discusses chimney breast external corners and measuring real angles when they are not 90 degrees. TradeCalculator likewise describes external skirting mitres that should be test-fitted and adjusted, which is the habit that prevents wasting full lengths.

The measure-once, cut-twice sequence

1. Mark the outside corner line lightly on the wall and on the back of both skirting pieces.
2. Seat a hinged angle finder on the two wall faces of the chimney breast return.
3. Read the actual outside angle. Do not assume the matching return has the same reading.
4. Divide the angle by two for equal opposing mitres.
5. Set the saw with the board face and top edge oriented exactly as it will be fitted.
6. Cut two short offcuts and bring them to the wall for a dry-fit.
7. If the offcuts close, cut the real lengths. If the heel or toe opens, adjust before committing.

Face orientation is the easy mistake

Most failed external skirting cuts are not caused by the maths alone. They happen because the board was flipped, the face was against the wrong side of the saw, or the left-hand cut was made as a right-hand cut. Draw an arrow on the top edge and write room-facing side on scrap until the sequence is automatic.

When preformed corners change the job

If you are using a PVC or MDF system with preformed external corner blocks, you may not need to measure and bisect the return. Follow that system's fitting instructions. The measured-mitre workflow is for boards where the two cut faces make the visible corner.

Forum reality check

Screwfix Community discussions of external skirting and architrave mitre gaps on walls that are not true 90 degrees show why test pieces matter. You want to find the error in a 150 mm offcut, not in a primed 4.2 m board.

Checklist before fixing

• Have you measured this exact return, not the opposite side?
• Have you halved the angle for the two matching mitres?
• Have you marked board face, top, left and right?
• Have you dry-fitted two scraps at the wall?
• Does the joint close without forcing the boards out of line?

If you need a tool for reading the wall angle and carrying it back to the saw setup, the same-site option is on the LEXIVON detail page. For internal skirting choices, read skirting board scribe or mitre; for dado externals already covered on site, see dado rail external corner angles.