How to cut Cornice

Author: | Last Updated: 12 Mar 2022

When doing home improvement work, aside from reinforcing structural things around the home, you might also want to spruce up the property by adding some more decorative elements. One way to do this is by adding cornices to the walls inside the home. Many DIYers are daunted by the idea of cutting it, but there’s nothing to fear! Cutting cornice just requires careful planning, the right tools, and a lot of confidence! With our simple tips below, you’ll be able to cut cornice like a pro in no time.

What is cornice?

Cornice is a type of moulding that is typically decorative. It’s the ceiling counterpart of a skirting board; skirting boards are between the floor and the wall, while cornices are between the wall and the ceiling. While they are really more for design and aesthetics, cornices can also help mask uneven wall and ceiling junctions, giving the room a cleaner and more polished feel. They can also be a great way to add accents or to tone down a room’s colour palette, depending on their design. They can bring a traditional or modern feel to the room and be as avant-garde or as inconspicuous as desired.

Types of materials for cornices

Cornices can be made from various materials, each with its own pros and cons. Choosing your cornice material is very important because it will have an impact on its installation, as you will see below. There are three main materials that cornices are made of:


Polystyrene is a type of synthetic resin that is very lightweight compared to the other cornice materials available. It is best for small, low-profile cornices since these usually come in plain, straightforward designs. One thing to note about polystyrene cornices is that they are very absorbent, so you will need to use more coats of paint to get the desired finish and tone that you want. Polystyrene is also very delicate and soft, so it must be installed with great care.


Plaster is the traditional material for cornices, and is one of the more expensive options. The ornate cornices you see in traditional homes, mansions, or cultural locations are usually made from plaster because it is more versatile in design, moudling, and patterns. Plaster cornices give an authentic feel to a property, transporting you back in time to the gilded age. However, plaster cornices are heavy and run the risk of breaking during installation due to the nature of the material, so it’s best left to the professionals.


Hardened polyurethane—or simply, polyurethane—is a plastic or foam that has become very popular as a cornice material. It can be shaped to look like carvings and mouldings of a plaster cornice, but has the lightness of polystyrene. It is also more durable than polystyrene (both for handling and in the long run), which makes it easy to install for DIY projects. With the aesthetic of plaster, and “improved” qualities over polystyrene, polyurethane cornices are quickly becoming the standard for most home improvement projects.

How to cut your cornice for installation

Once you’ve bought your cornice planks, you’ll need to cut them to size so that they can be installed correctly in your room. It may take a bit of practice, but with the right tools and patience, it’s possible!

Step 1: Get your tools and supplies together

Some basic things you will need are:

  • A fine-toothed hand saw
  • A circle saw
  • A mitre box or block
  • Pencil and chalk
  • Stanley knife
  • Sandpaper
  • Cornice cement or other adhesive

Step 2: Prepare and measure the area

Before cutting the cornice, prep the wall and ceiling area where you will be installing it. Wipe it down with a slightly damp sponge, and scrub with a detergent if necessary to remove oil, dust, or leftover adhesive from previous installations.

Measure the area where you plan to install the cornice. Take note of the width of the area you will need to cover since this measurement also has to be transferred to the cornice material itself. Ensure your pieces are long enough to be joined together along the length of the wall.

Step 3: Measure the cornice and start the cutting

Once you have the measurements for the wall, measure your cornice pieces, ensuring that you mark where the angles and corners will occur once installed. While some cornice pieces from certain brands can come with pre-formed corners, if you prefer to cut them yourself or there are unusual forms around your room, you can easily do it yourself.

Cutting the lengths of the cornice is straightforward with a circular saw or even a handsaw. Cutting cornice corners is the most difficult part of the installation. Whether you cut with a circular saw or a hand saw, use a mitre box to help you keep the piece safely in place. The ceiling and wall edge of the cornice piece should sit flat against the bottom and top side of the mitre box to allow for the most secure hold as you saw. Since you will be cutting at angles, it’s important to double-check your measurements and ensure you will be cutting the appropriate lengths that will fit into one another once installed.

Step 4: Finish off the cut pieces

After cutting the cornice pieces, sand them to ensure that the cut edge is smooth and does not have any snags or coarse spots. Sanding also ensures corner pieces will fit together snugly, without any overlaps—be careful not to sand off too much that you shorten the piece, which will create an unsightly gap when installed.

Step 5: Install the cornice

Polyurethane cornices can be easily installed on the wall using an adhesive. Commercially-available adhesives are the easiest and most convenient choice for this. Use the adhesive sparingly and ensure that you apply it to both the ceiling and wall parts of the cornice pieces. Press them firmly into position, hold with some part-driven nails, and then remove them once the adhesive is set. There you have it—a newly-installed cornice to liven up your renovation project!

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