How to Fit Polystyrene Coving

Polystyrene coving is quick and easy to fit. However, the tricky part of fitting coving is getting the angles right, so be prepared to practice first!

Pre-mitred corner pieces are available, but in this example we’re going to cut our own mitre joints and coping joints instead.

What you’ll need


Making a Mitre Block

Creating a mitre block could typically take about an hour to make, but will help you produce accurate cuts. You could also buy a mitre block, but making one means you can build it to fit the coving you're using.

To make a mitre block, screw two blocks of wood parallel to each other on a board, using screws at the very ends of the blocks of wood. The height of the blocks should be at least as high as the height of the coving. The blocks should be the same distance apart as the width of the coving section against the ceiling.

Now mark lines on the blocks 90 degrees to the blocks and 45 degrees. Use more screws to hold the block in place, either side of every cut line. Now cut along the lines.

Drawing of a mitre block with a section of coving.

Mitre joints and coping joints

Mitre joints are made by cutting two sections of coving at 45° to each other. These joints can be used for both internal and external joins. Coping joints are for internal joints only, and are made by cutting a 90° line on one piece of coving and butting it against the wall. The second is cut at 45° then cut along the 45° edge so that the shape of the cut matches the profile of the other profile of the other section of coving.

Mitre joints are quicker to produce, but coping joints can provide tighter joins, especially when the two walls are not exactly 90° to each other.

Creating some example pieces

Take some time to practice a little. Getting your head around the types of joints is something to do in a relaxed atmosphere!

Not all coving is symmetrical. The long side is usually placed against the wall, and the short against the ceiling. When cutting, always ensure the side against the ceiling is the side on the base of the mitre block.

Take time out to practice before starting work. Here we are using a simplified mitre block to create some samples.

Cutting and Fitting the Coving

Cutting the coving with a fine tooth saw, then a coping saw

Most coving packs have the dimensions of the coving on them. Mark a line along the wall, parallel to the ceiling. The distance of the line from the ceiling should be equal to the widest edge of the coving. This will give you a line to fit along.

Start with the a long section of wall, and work your way around the room. Measure and cut lengths using mitre joints or coping joints at the corners. Use plenty of adhesive along the edges of the coving and stick each piece in place before measuring and cutting the next.


Use "decorators caulk" to fill gaps around the coving, and cover with an emulsion paint.

Dos and Don’ts