Introduction: Try Your Hand at Installing Cornice

Picture of Try Your Hand at Installing Cornice

Cornice....that's the decorative molding that joins your house walls to the ceiling, usually made of paper and plaster, or just polystyrene. Apparently called "coving" in some countries.

This 'ible is intended for the amateur builder to replace the cornice in a room. It's not really hard work, nor all that difficult, but you need to know some of the tricks. The worst bit is getting up and down the ladder while you test fit the cornice. It needs saying though that I'm an amateur too, but I've managed to do this quite successfully... Well I think so anyway.

Timber "cornice" is available, but that is generally called "molding" and is smaller .... Here I'm talking about the cornice made from plaster, like the "Gyprock" panels Australians use on stud walls.. Ambka (also may be known as) "hardwalling"?

Step 1: Tools

Picture of Tools

Step 1 is to get the materials and tools. I love buying tools so that's my excuse to visit the hardware store. You will need:
- your preferred cornice shape. There is a lot of variety so pick whatever you like. Practice on the cheap stuff if you want.


- thin plastic or rubber gloves if your skin is sensitive. Actually using gloves is better.


- a dust mask is recommended


- cornice cement...note the health warnings. You will be mixing it with water in smallish batches. Should have a toothpaste constituency when mixed properly.


- a plastic 2l ice cream container. Feel free to delay this project while you enjoy the icecream. Any largish plastic container will do, even a plastic 3l milk container cut to size. This is the tub used to mix your cornice cement. Unless you want to work fast on a large cornice, a bucket is probably too big.


- a putty knife, or similar spatula


- a cheap smallish crosscut saw, and I mean cheap, you are cutting plaster with it.


- a cheap cornice cutting template. These are usually cheap plastic with steps on one side. They should be a right angle, but are not, so also buy something that you can attach to the template tool to make it square. I have used a small shelf support in the photos, but previously I used a piece of timber cut in a right-angle triangle. I attached it by drilling small countersunk holes in the plastic and screwing into the wood. It worked better than the shelf support..I lost my original and got lazy. That is tip # 1.


- alternately a miter box can be used, but I've not used one yet.


- a good measuring tape


- some 2400mm (8') lengths of pine about 10mm thick and 40mm wide. It needs to be a bit flexible, but not floppy. These will be ground mounted props to hold up the cornice while the cement dries That's tip # 2.


- sandpaper and a cheap power finishing sander. Makes the job easier, and a cheapie is less emotionally draining to chuck out when it eventually wears out from the plaster dust.

Keep your tools clean. Tip #3. Plaster covered tools are a pain to work with and clean tools last longer. Oh, and according to the packet, cornice cement goes off faster in the presence of dried cornice cement.

Step 2: Measure, Mark, Meaure and Check, Cut

Picture of Measure, Mark, Meaure and Check, Cut

Tip #4. None of the corners of your room are square. It would be easier if they were, but the are (probably) not. Striving for a perfect 45deg cut is laudable, but not essential.


Tip #5. Decide which side of the cornice will be against the ceiling and ALWAYS keep the apex of the cutting template against that side. If you don't, then you will cut the corners wrong. It won't look wrong till you put it up against the corner, and when you do, you'll notice the corner opens up rather than closes, and there will be a gaping hole. It spoils your mood, but fortunately the materials are quite cheap, so do it again.


Tip #6. Just for practice, set the template on the cornice as described near one end of the cornice. Lay the saw hard up against the template, hold the template firmly and gently draw the saw. It's soft material and will cut easily. Don't move the template or you will mess up. Don't squash the template either as it will go out of square. Do your best to get a good 45degree cut. If the template has bumps that prevent it laying flat against the cornice at its ends, then cut them off.


Tip #7. An " inside corner" is this: when you look into the corner then you have walls on either side of you. An "outside corner" is this: when you look into the corner then there are no walls either side of you. For example, go look at a corner of your house with an outside wall. When you stand inside the house then that's an "inside corner". Now go outside and look at the same corner of the house. That's the "outside" corner.

Now decide what kind of corner you will cut. Let's assume an inside corner first as per the third photo. Measure the gap you want to cover, I'm assuming it's smaller than the overall length of the purchased cornice. Start say at the right wall when facing the gap. Lay the cornice on supports, facing up, so that you are facing the cornice and the right wall. Set the template on the cornice, apex on the edge that will adhere to the ceiling. The left leg should touch the end of the length of cornice allowing for the width of the blade. (In my case I allowed for the scallops so placed the template off the end) Cut, making sure the saw blade lies flat against the template's left leg. See the first photo. That's the left side cut for the right hand wall. In my case the other end was a square cut, so that portion of the cornice is finished.

Now do the same for the other wall. Making sure to cut on the right hand side of the template. Mark the length of cornice to match your gap, or scalloping, as you want. Make sure that the right hand side leg of the template is touching the mark, allowing for the thickness of the blade. See the second photo. In my case the other end was again a square cut, so that portion of the cornice is also finished.


Test fit and trim as necessary.

Step 3: Fix It in Place

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Having cut the pieces, time to install!

Measure from the ceiling down. The supplier should be able to supply the dimensions of your cornice. Mark the wall with a light pencil line - this will be the bottom edge of the cornice. Most likely you will find the ceiling is not 100% flat, if more than a few mm, then fix that first, otherwise the glue will be use to absorb the difference. Its hardly noticable when painted.

Following the instructions on the packet, mix up the cornice cement (glue). I add water slowly to a small pile of dry cement in the plastic tub. Careful to avoid adding too much water - it must be firm like toothpaste and "hold peaks". Make sure you have enough mixed cement for the task, as the cement already applied will start going off while you mix additional cement. A bit of experimentation might be needed, but scale it off the suppliers package.

Lay out a pieces of cornice, rear side up, on a trestle below the side you are tackling first. Lay a bead of cement on the back of the cornice, top and bottom. Use the bottom and top edges of the cornice to wipe the cement from the spatula when held vertically. Make the bead around 10mm to 15mm thick, but accuracy is not important here. Don't skimp, but no need to plaster everything with cement either. I dont know how to explain this...place the bead on the edge so it protrudes outwards, not parallel to the back of the cornice... see the photo. I hope that makes sense! Maybe it will help to say that its the opposite of buttering toast?

Regrettably I didnt take photos of the large length, so I hope this description and photos of another job help.

Step 4: Holding It Up There

Picture of Holding It Up There

Righto, the cornice is cut and buttered. Climb up the ladder/tressle and push the cornice in place. Longer pieces will require 2 or more people, but its quite stiff so 2m or so can be done by 1 person. Use even support of course. I would cut very long sections into shorter managable parts.

Here's tip#8! Press it into place following the line you marked on the wall. Dont put it on and take it off. Push it around to the right spot.

Jamb the pine strip between the floor and the cornice as in the photos. Leave it there till the cement has dried, but scrape off or wipe off any excess cement before it dries with the spatula and a damp cloth. You can sand it off later with difficulty but its a pain, takes a lot of time, and messes with your enjoyment of the "job-well-done" celebratory beer. Careful not to rub the cornice outside paper cover too hard with the damp rag - it will peel off!

As clearly visible in the photos, the corners are not square! Excess cement can be used to fill gaps. It takes a while to go off, so its quite easy to fill and form the corner. Try make it as smooth as possible with the spatula. Do not add water to the cement to thin it out once it starts to set. Throw out dried or drying cement.

Step 5: Finishing Up

This is the home stretch!

Edit: before the cornice cement dries, wipe up any excess cement with a damp rag. That saves a lot of effort later. Throw out the waste cement, wash the rag immediately if you want to save it.

When the cement has dried, take away the props, get out the orbitral sander and gently sand everthing where the cement was applied. Dont forget the dust mask!

If there are defects, then add some filler putty and dand smooth as per the instructions. Use a fairly fine sandpaper, suited to the task.

When youre satisfied, vacuum everything tio get rid of the dust and paint.

Thats it, youre done. Well done, now go get that beer!

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