How to cut and install cornice

If you’re replacing old cornice, you’ll need to remove the old cornice and plaster. Start by carefully scoring along the edges where the cornice meets the wall and ceiling using a utility knife. This helps prevent damage to the surrounding surfaces.

Next, use a wide scraper to loosen the cornice. Insert the scraper gently at the edge and work your way along, applying even pressure to pry the cornice away from the wall and ceiling. For stubborn areas, you can tap the handle of the scraper lightly with a mallet to ease the cornice off. Once the cornice is removed, clean the exposed area by scraping off any remaining adhesive and cornice plaster as this ensures the new cornice will sit flush.

Now you’re ready to install the new cornice. To help with alignment, mark where the new cornice will go on the wall and ceiling: For a 55mm cove cornice, make a mark 55mm down from the ceiling on the wall and 55mm out from the wall on the ceiling. Use a chalk line or pencil to create a continuous guide along the length of the wall and ceiling for precise placement.

Next, measure the length of your cornice carefully, remembering:

• For internal mitres (inside corners where two walls meet), measure to the long point of the angle.
• For external mitres (where the cornice wraps around an external corner), measure to the short point.

Mark the cutting direction clearly on your cornice to avoid mistakes. Always double-check your measurements and marks before cutting.

Use a pencil to mark the direction of the cut on your cornice. This helps keep track of your orientation and avoids confusion when you’re ready to cut. Always double-check your marks to make sure they’re accurate. Place the cornice carefully in a mitre box. Most mitre boxes have steps for different cornice sizes (e.g., 55mm, 75mm, 90mm), so position yours accordingly.

Using a hand saw, cut along the marked angle in the mitre box. Hold the cornice firmly in place to prevent any movement while cutting. Once the cut is complete, check the fit by holding the cornice up to the wall or ceiling. Make any minor adjustments if needed.

Prepare the cornice cement according to the manufacturer’s instructions. The ideal consistency is thick but still spreadable, similar to butter. This ensures a strong bond between the cornice, wall, and ceiling.

Use a scraper to apply a generous amount of cornice cement along the edges of the cornice where it will contact the wall and ceiling. Spread it evenly for a secure fit. Press the cornice into place, making sure it aligns with the marks on the wall and ceiling. To keep the cornice steady while the cement sets, insert screws along the length of the cornice. Be gentle to avoid damaging the surface of the cornice.

Once the cornice is installed, scrape off any excess cornice cement with a trowel or broad knife. Fill in any gaps or screw holes with cornice cement. After a few minutes, use a damp sponge to smooth the surface and remove any remaining excess. This will leave you with a clean, seamless finish.

Once the cement has fully dried, fill any screw holes or gaps with filler. Use a filling knife to smooth the filler so it’s flush with the surface.

After the filler has dried, sand the area lightly with sandpaper to remove any rough patches. Wipe the area with a microfibre cloth to remove dust and your cornice will now be fully installed.