How to repair a cracked cornice

[MitchellMc]

Difficulty: Beginner

Cornices conceal the joint between a ceiling and a wall and add a decorative element. 

It’s common for cornice mouldings to crack or get damaged over time. This can be unsightly and potentially dangerous.

Here is a simple guide to repairing a cracked cornice using a multi-purpose sealant.

As this project involves chemicals and power tools, please follow all safety guidelines provided by manufacturers and use the recommended safety gear.

Let us know if you have any questions. We’d be happy to assist.

Steps

Step 1

Open the gap.

Use a scraper to open the gap or crack between the cornice and wall so that you create space for sealant. Without a gap, the sealant would only be applied to the surface and any new movement would split the cornice again.

Scrape off the paint at any points along the crack where the cornice is still attached to the wall and remove any loose debris.

Do this until you can fully insert the scraper behind the cornice.

    

Step 2

Remove any remaining debris behind the cornice.

Insert wedges in the crack by tapping them in place with a hammer.

Place a wedge every 300mm along the crack to keep it open. Be careful not to drive in the wedges too far as this could cause the cornice to crack further.

Now use your scraper to remove any remaining debris caught behind the cornice.

    

Step 3

Glue the cornice to the wall.

Insert your sealant cartridge into the caulking gun. Place the nozzle behind the cornice and fill along the length of the crack.

Now remove the wedges. Use a rag to remove any excess sealant that may have leaked from the crack.

    

Step 4

Screw the cornice to the wall.

Use a drill driver to pre-drill countersunk holes every 15cm along the bottom edge of the cornice. Make sure you are wearing personal protective equipment (PPE), including gloves and safety glasses.

Avoid placing holes too close to the edge. This can cause the cornice to crack.

Now insert screws in the holes and drive them into the wall.

      

Step 5

Seal the crack.

Tape the area above and below the crack. Use the caulking gun to apply sealant along the crack in between the tape lines.

Now wet your finger in soapy water and use it to smoothen the sealant.

Remove the tape about two minutes after applying the sealant. Do not allow the sealant to dry before removing the tape or you might remove the sealant with the tape. 

      

Step 6

Fill the screw holes. 

Use your caulking gun to fill the screw holes with sealant.

Smoothen the sealant with a wet finger, as in the previous step.

Allow the sealant to dry for at least an hour.

  

Step 7

Paint the cornice.

Paint over the repaired area for a smooth finish. This will also help ensure the repaired area blends seamlessly with the rest of the cornice.

You have now repaired your cracked cornice.

  

Materials

• Ceiling paint
• 3-in-1 silicone sealant
• Painter's tape
• Plastic wedges
• Plaster screws.

Tools

• Hammer
• Caulking gun
• Drill driver
• Paint scraper
• Paintbrush
• Rag
• Safety gear, including gloves and safety glasses.

Images

                                        

[Loklyn]

Great info on repairing cornices. Could you pease tell me what size plaster screws I need to use?

[EricL]

Hello @Loklyn 

Welcome to the Bunnings Workshop community. It's great to have you join us, and thanks for sharing your question about what screws to use to re-anchor the cornice.

I suggest using the Zenith 8G x 50mm Gold Passivated Bugle Head Plasterboard Screws. You could use the longer 65mm version, but I don't recommend using anything shorter than the 50mm screw.

If you need further assistance, please let us know.

Eric

[LivM]

Great info, Could you tell me if I can use the same method to repair a cornice attached to a rendered brick wall? Thank you.

[MitchellMc]

Welcome to the Bunnings Workshop community @LivM. It's sensational to have you join us and many thanks for your question on repairing cornice.

The only difference will be that you won't be able to screw into the wall as easily. I'd recommend you either try these steps without screwing into the wall or swap the standard screw out for Ramset Black Countersunk Masonry Screws and pre-drill their holes with a 3mm masonry bit.

Please let me know if you have further questions or get stuck.

Mitchell

[tisonlyme]

Thank you for the great info. 

Would this be the same info required for fixing cracked skirting boards?

[EricL]

Hi @tisonlyme 

Yes, you can apply this repair technique to your skirting board. If you run into any issues, please don't hesitate to post a question.

Please keep us updated with your progress, we look forward to seeing your skirting board repaired.

Eric

[Archie1]

I need to install a length of cornice from water damage and want to fix the cracks around the house as well. Can I use the cornice cement in the cracks rather than the sealant so I can sand imperfections and paint over? Fixing screws to block/render walls what is the recommended spacing?

[MitchellMc]

Welcome to the Bunnings Workshop community @Archie1. It's brilliant to have you join us, and many thanks for your question about using cornice cement.

Cornice cement is similar to a filling plaster, so it can be used to repair small cracks. 

Here's the CSR Gyprock cornice installation guide. Cornice cement is a standalone fixing product. No additional fixings are required, but you do use some temporary ones to hold the cornice in position until the cement dries. Screws have been used in this guide as it is a repair on installed cornice, and they are required to compress it back into position as the original adhesive had been compromised.

Please let me know if you have any questions.

Mitchell

[AMA2]

Hi 👋 

I’ve taken these steps with the 3 in one sealant at and it’s worked well. I’m really happy.

there are a few more fine cracks I missed where the ceiling meets the cornice and the plaster under the cornice. It’s an old double brick house. 

one of the cornices in the corner is crumbling away. I’ve fixed it with Shelley’s 3 in one so far but am wondering about joint compound and tape  to finish it off.

Do you guys recommend using gyprock multipurpose joint compound on these small areas? ( ceiling areas and cornices ) . Is it ok if the joint compound contacts the Shelley’s silicone sealant ?

[MitchellMc]

Welcome to the Bunnings Workshop community @AMA2. It's amazing to have you join us, and many thanks for your question about repairing cornice.

Would you be able to share an image of the areas in question? That way our member would have a much better idea of what you're working with and what products to suggest. Let me know if you need a hand uploading images.

Multipurpose joint compounds can certainly be used for a variety of filling applications. If there is just a small amount of damage in these areas, then the filler can be used. Tape should be used for larger areas or joints in sheets.

The joint compound might not adhere particularly well to the silicone, so it's best to avoid it if possible.

Please let me know if you have any questions.

Mitchell

[AMA2]

Thanks @MitchellMc  that answers my main concern about silicone.

I will separately use gyprock multipurpose joint compound and a tape for bigger cracks and of course, on internal walls. The walls are plastered (?cement / plaster?)  double brick.  I already have some fibreglass builders tape.  

(Wrong way round sorry )

[EricL]

Hi @AMA2 

Please keep us updated with your progress, we look forward to seeing your cornice repaired.

Eric