How do I cut and fit kitchen cornice and pelmet?

Cornice and pelmet are the trims that make a kitchen look built rather than assembled, and they are the parts that most reliably defeat people. The difficulty is not the fixing, which is trivial — it is that every corner is a compound of two angles, the walls are not square, and each mistake removes 300mm from a length you cannot buy a bit more of.

What you'll need

• Cornice and pelmet lengths
• Mitre saw, or a mitre box and a fine-tooth saw
• Fixing blocks or brackets, and short screws
• Tape measure, pencil, sliding bevel
• Wood glue (optional)
• Colour-matched filler or wax (optional)

Step by step

1. Get the terminology straight.Cornice sits on top of the wall units and hides the gap between the units and the ceiling, or simply finishes the top. Pelmet hangs below the wall units and hides under-cabinet lighting and the underside of the carcass. Some ranges use the same profile for both, inverted.
2. Check the wall units are level and in line first.Cornice runs in a straight line across everything. If one unit is 3mm lower than its neighbour, the cornice will either follow it and look wrong or bridge it and leave a gap. Sort the units before cutting trim.
3. Dry-fit the whole run before cutting anything to final length.Work out where every joint falls, mark them, and think about where the cut ends will be visible. It is far cheaper to plan on the floor than to cut on the wall.
4. Check every corner with a sliding bevel.Walls are rarely 90 degrees. Set a bevel into the corner, transfer the angle, and halve it for the mitre. Cutting every corner at 45 degrees and hoping is what produces the gaps people fill with caulk.
5. Cut internal corners first, then work outwards.Internal corners are less forgiving and less recoverable. Get those right on the full lengths and let the straight cuts and the ends absorb the error.
6. Cut long and creep up.Cut 2 to 3mm long, offer it up, and take a whisker off at a time. Cornice cannot be lengthened, and there are no offcuts long enough to start again.
7. Fix with blocks behind, never through the face.Small timber or plastic blocks screwed to the top of the carcass, with the cornice screwed to them from behind or above. Pinning through the front face of a cornice leaves holes that never disappear on a foil or gloss finish.
8. Glue the mitres.A thin bead of wood glue on both faces of a mitre, pushed together and held, closes the joint far better than screws alone and stops it opening as the room's humidity changes.
9. Fill any residual gap with colour-matched filler, not caulk.Decorator's caulk on a laminate or foil trim is grey, dull and obvious. A wax or hard filler in the trim's own colour is what the trade uses.
10. Fit pelmet last, after the under-cabinet lighting.The pelmet exists partly to hide the lights and their wiring, so the lights and their cable route go in first and the pelmet closes it up.

Tips

• Buy 20 per cent more length than the run measures. You will make at least one bad cut, and matching a discontinued profile a month later is unpleasant.
• A mitre saw with a fine-tooth blade cutting on the finished face downwards gives a clean edge on foil and laminate profiles. A coarse blade tears them.
• Cornice at a wall-to-ceiling junction rarely fits a wavy ceiling. Scribing the top edge, or accepting a shadow gap deliberately, both look better than a lumpy caulk line.
• If the run passes an extractor hood or a tall unit, dry-fit those junctions first — they are where the profile has to break and where the awkward cuts live.

Common mistakes

• Cutting every corner at 45 degrees — Almost no wall corner is 90 degrees. The two 45s leave a wedge-shaped gap at one end of the mitre, and there is no filling that convincingly.
• Pinning through the face — The holes show on any foil-wrapped, gloss or veneered trim and cannot be filled invisibly. Fix from behind, always.
• Fitting cornice before the wall units are level — The trim reveals every discrepancy in the units below it, in a single straight line at eye level.

Questions people ask