How do I put up coving?

Coving is a job where almost all the difficulty is in the preparation and the setting out, not in the fixing. Rooms are not square, ceilings are not flat, and a coving line drawn by eye follows every defect in the room. Marking a consistent line first, and cutting corners before you commit to any fixing, is what separates a run that looks deliberate from one that has gaps at every corner.

What you'll need

• Coving
• Coving adhesive
• Mitre box or a mitre saw, or a coving mitre template
• Fine-toothed saw
• Chalk line or a long straightedge and pencil
• Filling knife and a damp sponge
• Nails or screws for temporary support
• Ladder or hop-up

Step by step

1. Measure the room and buy sensibly.Total the wall lengths, then add roughly ten to fifteen per cent for cutting and mistakes. Buy it all from the same batch — profiles vary slightly between batches and two profiles in one room show at the corners.
2. Work out the projection.Hold a length in the corner between wall and ceiling and mark where its edges land on each surface. That is the projection on the wall and on the ceiling, and it is the same all round the room.
3. Mark the lines all round, on both surfaces.Measure down from the ceiling for the wall line and out from the wall for the ceiling line, at both ends of each wall, and join them with a chalk line or a straightedge. Do this before any coving is cut.
4. Check the lines look right from the doorway.If the ceiling dips, a mathematically measured line will look wrong. Stand back and adjust the marks so the coving reads as a straight line to the eye rather than to the tape — the eye is what will judge it afterwards.
5. Prepare the surfaces.Scrape or sand the paint away in the bands where the coving will land, so the adhesive bonds to plaster rather than to emulsion. Dust off. On new plaster or a very absorbent surface, damp it or prime as the adhesive maker directs.
6. Plan the order of the run.Start at the most visible corner, or with the longest wall, and work outward in both directions so any final cut lands somewhere inconspicuous. Cut and dry-fit an entire corner before mixing any adhesive.
7. Cut the mitres before you fix anything.Coving is cut upside down and reversed in a mitre box — the ceiling edge goes against the bottom of the box and the wall edge against the fence, so that the piece sits in the box in the same relationship it will have to the room. Getting this wrong is the single most common error, and the cure is to dry-fit every corner before committing.
8. Butter the adhesive onto both edges.A continuous bead along the wall edge and the ceiling edge, generous enough to squeeze out. A run of dabs leaves gaps that show as a shadow line and gives less support.
9. Press it home and support it while it grabs.Press firmly along the whole length, then hold it with a few masonry nails driven partly into the wall beneath, or screws through the coving into studs where it is a heavy plaster profile. Remove them once it has set and fill the holes.
10. Fill every joint and mitre with the same adhesive.Squeeze it in, smooth with a wetted finger or a small filling knife, then wipe with a damp sponge before it sets. Coving adhesive sands and paints like the coving; decorator's caulk shrinks and reads as a different material under paint.
11. Sponge the surplus off immediately.Adhesive left to harden on the face of the coving has to be scraped off later, which damages the profile. A bucket of water and a sponge beside you throughout is the whole trick.
12. Let it set fully before painting.Then prime if the manufacturer requires it, and paint. Coving usually takes the ceiling colour, cut in along the bottom edge.

Tips

• For internal corners, cutting a mitre on one piece and scribing the other to fit is far more forgiving in a room that is not square, exactly as with skirting.
• Nothing in an old house is 90 degrees. Measure the actual angle in each corner with an angle finder and set the saw to half of it, rather than assuming 45.
• Working alone, cut a temporary support batten to the exact height of the wall line and screw it to the wall — the coving rests on it while you work along the run.
• Buy a coving mitre template if you have several corners. They are cheap, they take the geometry out of the cut, and they are much easier than getting a coving to sit correctly in a mitre box.

Common mistakes

• Cutting coving flat in a mitre box — Coving sits at an angle between two surfaces, and a flat cut gives an angle that cannot close. It has to be cut in the box in the same orientation it will take on the wall — upside down and reversed.
• Fixing straight onto emulsion — The adhesive bonds to the paint film, the paint film lets go of the wall, and the coving drops at the top edge — the classic coving failure.
• Filling mitres with decorator's caulk — Caulk shrinks back into the joint and takes paint differently. Coving adhesive fills, sets hard and finishes like the material either side.
• Marking the line by eye off the ceiling — Ceilings are not flat and walls are not plumb, so a line taken from either without checking wanders. Measure, mark, then stand back and check.

Questions people ask