How to Install Plaster Cornice and Coving (UPDATED: April 2024)

You can add instant elegance and character to a room by decorating the junction between walls and ceiling with distinctive strips of coving made from traditional plaster or modern synthetic polystyrene.

Decorative plaster coving or deeper, more elaborate cornicing softens the transition between the wall and the ceiling.

We, at The Swindon Plasterer, recommend you conceal uneven joins and also hide any harmless but unsightly cracks that often form in the junction between the wall and ceiling as the house settles.

Installing Plaster Cornice and Coving

Before selecting a design, it is worth considering which width and pattern suits the scale and style of your room best.

Plain, narrow concave strips of coving provide a neat trim at ceiling level; more ornate plaster moldings, depicting stylized leaves, flowers or geometric designs like Greek key patterns, introduce an appealing period feel to a room.

Depending on how much of a feature you want to make of the coving, you can either paint it to contrast with the color of the wall or ceiling, or to coordinate with it.

Putting Up Coving

Plan the layout of the coving or cornice carefully before you begin, so that you don’t have to join lengths in visible areas of the room. Generally, begin fixing the molding in a corner of the longest wall facing you as you come into the room. Try to avoid fitting small sections, where two adjacent seams are hard to hide.

Set up a working platform so that you can reach the ceiling easily.

Planks laid between two decorator’s trestles are safer than working from a stepladder. Long lengths of plaster coving are heavy while polystyrene coving is unwieldy; an extra pair of hands makes fitting much easier.

Carry the lengths of cornice carefully between the two of you. Hold to top edge and carry it on edge; don’t carry a long section flat in case it sags and cracks.

Covings are styled with a flat face at the top and back to fit tightly against the ceiling and wall.

They are stuck in place with a special plaster or polystyrene coving adhesive. Use rustproof nails as well as adhesive to hold heavy fibrous plaster coving.

You can cut polystyrene coving with a sharp carving knife but you should use a fine toothed tenon saw to cut plaster coving. Gypsum plaster and polystyrene corner pieces are available to avoid the need for cutting mitered corners.

Fitting Gypsum Plaster Coving

If you decide not to use corner pieces, you have to miter the ends of the coving in a miter box.

You can either use the guidelines on the ceiling for marking up internal corners and the wall for external ones, or look out for plaster coving that comes with a template to make cutting mitered corners easier.

You simply trace the shape of the corners on to the coving with a pencil, and cut along the guideline with a craft knife or saw.

Don’t worry too much about perfect seams and miters, as you can fill gaps at corners and joins, or between coving and wall or ceiling, with fine surface plaster filler. You can get gypsum plaster cove corners to fit over existing mitered corners later on if you wish.

1. Drawing guidelines: Ensure that the wall and ceiling surfaces are clean, smooth and dry. Then hold a small piece of coving in place at the starting corner. Mark pencil guidelines on the ceiling and wall along the top and bottom of the coving. Continue marking in the same way all round the room. To give the coving a good grip, lightly score the area between the guidelines with a craft knife.

2. Measure up: Measure the length of each wall between corners. At external corners allow for an overlap of at least one coving’s width. Cut to length with a fine-toothed tenon saw or craft knife.

3. Marking internal corners: With a friend, carefully lift a length of coving up to the wall and push it tightly into the first corner. In pencil, mark on the top edge when the coving crosses the guideline on the ceiling. Mark the adjoining piece of coving in the same way on the adjacent wall.

4. Marking an external corner: Hold a length of coving up to the wall and, with a pencil mark off the end of the wall on its lower edge. Without moving the coving, then mark where the top edge intersects the guideline on the ceiling. Repeat for the coving on the other side of the corner.

5. Cutting the miter: Lay the coving on its back on the floor, using a straightedge and pencil, draw a diagonal line from the marked point on the top edge to the lower corner for an internal corner, or between the two marked points on the top and lower edges for an external one. Put the cornice in a miter box and cut along the marked lines. Then lift two pieces up to the corner at the same time to check the join.

6. Fixing the coving: spread adhesive along the flat surfaces on the back of the first length of coving. Press it firmly but gently against the wall and ceiling and push the pointed lower edge into the corner. Make sure the coving grips the wall along its top and bottom edges. With a damp cloth, wipe away any adhesive that squeezes out from behind the coving. To hold it in place until the adhesive sets, knock a few nails into the wall at regular intervals under the lower edge.

7. Fitting the remaining coving: Spread adhesive on the adjacent lengths of coving and press them into position in the same way to form neat butt joins. Continue fitting the rest of the coving round the room.

8. Hiding joins: When the adhesive is set, remove the supporting nails and fill the holes in the wall and any gaps between the joins with fine surface plaster filler, smoothing it in with your fingertip. Leave it to dry before painting the coving.

The procedure for measuring up, cutting and mitering traditional fibrous plaster coving is identical to fitting the gypsum plaster type except that you need to knock some galvanized nails through the coving itself into the wall and the joists in the ceiling to hold it permanently. Use a nail punch to bury the nail heads under the plaster and fill with fine surface filler when tidying up the corners and joins.

You can buy an embossed cove border to add color and patter to the plain gypsum plaster coving. You simply use a wallpaper adhesive to stick it along the concave face of the coving. If you lake you can add another strip over or under a dado rail to achieve a comprehensively molded look.

Fixing Polystyrene Coving

Polystyrene is the simplest of all coving types to put up, because it is so light and manageable. You just have to be careful not to push your fingers or nails through the soft polystyrene when you are pressing it to the wall and ceiling. Polystyrene molding covered with paper is more robust but just as lightweight.

To avoid creating a serious fire hazard, always use emulsion paint for decorating polystyrene coving; never paint over it with gloss paint.

1. Preparing the surfaces: Prepare the walls and ceiling and mark in the guidelines as for gypsum plaster coving.

2. Fitting corner pieces: Fix all the corner pieces before fitting the straight pieces. Spread plenty of adhesive along the flat back and top edges of the first corner piece and press it firmly but gently into position in the corner.

Pre-mitered external and internal corner sets to match paper-covered polystyrene coving save having to cut the miters yourself. Plain polystyrene coving comes with embossed corner pieces that serve the same purpose. You can paint both sorts with emulsion paint to complement the rest of the room.

3. Cutting the coving to fit: Measure the length of each wall between the corner pieces. If necessary, using a kitchen knife and a steel straightedge, cut straight across the coving to make it fit. Glue straight pieces along the wall, butting up the ends to the corner pieces and each other. Scrape away excess adhesive that squeezes out from under the coving with a filling knife and use it to neaten the joins.