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This coving is all around my house, but some needs repair and I can't match it.

It's a "C" profile with a lip at the bottom. I thought perhaps the lip was a separate picture rail or something, but it is all one moulded piece (plaster).

C-shape coving with lip

Does this profile have a name? I am based in the UK.

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    Is it molding or is it is a shaped plaster detail? – mikes Jan 25 at 12:25
  • It is made of plaster. I assumed cast in a mould although some parts of the house have the exact same profile in polystyrene. Presumably from more recent improvements – Tim Jan 25 at 12:28
  • How much replacement material will you need? – Jack Jan 25 at 21:48
  • It's a fairly small area that needs complete replacement. Less than a metre of coving length. – Tim Jan 27 at 11:31
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I would call that a "cove with bead". The main part is a simple cove, and there is a bead added at the bottom for a little extra detail.

To make the repairs, you would have to duplicate it in plaster. You would cut a template, pour plaster into a trough to hold the corner shape, then use the template to shape the exposed surface of the plaster to match the existing molding. Once the plaster has hardened, you have to "glue" it to the ceiling with more plaster. You'll probably want some sort of specialist to do this for you as it's not particularly easy, especially as a first project in plaster.

As an alternative, you may be able to find a matching cove and bead in wood or polystyrene (as it seems someone has done). These would be much easier to install with simple finish nails and a bit of filler over the nail heads.

A third alternative would be to find just a matching cove, then add a matching bead. If installed carefully, nobody would ever see the joint between the two (the joint would be above the bead and you'd have to have your head where your camera was in order to see the joint, so it wouldn't even have to be super tight). Again, wood or plastic would make for an easy installation.

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    Thanks for the thorough answer. Plan A is certainly to match it. Plan B to add bead separately. I think plan C is likely to be replacing all coving in the room. – Tim Jan 25 at 15:17
  • @Tim it's amazing what a guy can learn from years of watching This Old House... :) – FreeMan Jan 25 at 15:30
  • The look of the material that is in place looks like it was cast in place, as opposed to casting on a bench and setting in place. Depending on the amount needed, it may be worthwhile to get a plaster finisher to replicate it since it has such a deep curve, to find a wood replacement would mean custom work anyway.... – Jack Jan 25 at 21:56
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    I wish you the very best @Tim. You're a far braver soul than I! Look at the skills you're learning - you could go into business!! :) – FreeMan Jan 27 at 12:20
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    You could post your actual as another answer. I don't think you'd get any complaints and would probably get several votes for showing off your methods. – FreeMan Feb 13 at 17:12
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I already accepted an answer for this, but I thought I'd post back because what I've learned since may be of help or interest to others.

After cleaning up the damaged coving and chipping off the wall plaster, it seemed more apparent (as some commenters suggested) that this coving was made in situ. In fact, it seems as though the plaster of the coving was the same continuous layer of finishing plaster as was on the wall. You can just about see below how it sits on the bonding coat.

cleaned up coving profile

After plenty of Googling I learned that the cove was probably not so much cast as sculpted using a running mould. There are some amazing videos of people doing this on YouTube. https://www.youtube.com/results?search_query=running+mould

I didn't fancy doing this in situ, but I found various videos of people using the same technique to create sections on the bench. Inspired specifically by this video I decided to give that a try.

Making the blade that scrapes the plaster is worth some attention. It was the most time consuming part and essential to get right. Here's a good video of that whole process: https://www.youtube.com/watch?v=rlH_vMc6yTE

I read that zinc is a good material for this, but I ended up using 0.5mm aluminium which is way too soft and flimsy for extended use. However, having very limited metal working tools this did allow me to cut a half-decent blade with tin snips and file into shape; finally smoothing down imperfections with 240 sand paper.

I won't post all the details of my ugly contraption, but I ended up with this.

plaster cove on the bench plaster cove close up

It took 6 or 7 fairly thin coats of plaster of paris. The trickiest part was mixing small batches of plaster quickly between coats before the plaster could set on the mould. Plus also keeping the blade and running track clean between passes. I want an assistant next time as this was surprisingly exhausting.

Other notable details are that I added a layer of hessian at the back for strength. A curve of wire mesh would have been better (as in earlier video) but I was doing experiment no.1 on the cheap. Also, thanks to commenters in this related question, I used washing up liquid as a release agent.

A hollow back was created by putting a right angle bead at the back of the casing. This made the section lighter and used less of the fairly expensive plaster too.

Here's the final product out of the mould. I haven't glued it into place yet. That's for another day.

plaster coving with hollow back

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  • Seriously nice work, my friend! Very well done, congrats on that. I'm not certain I'd have attempted this one... – FreeMan Feb 16 at 11:41
  • Thanks, it was "fun". I will probably screw it up when attaching to the wall, but it will have been interesting. – Tim Feb 16 at 12:19
  • I would think that fiberglass mesh drywall tape might make a good, cheap strengthener. Something to consider while you're still in the experimental stage. – FreeMan Feb 16 at 13:21
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Do a search for "crown molding" on your computer or go to the orange or blue big box stores or any lumber store. If you can, when you go to a store, take a piece of that molding to match what they have..

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    It is a form of crown molding, one of the 2 down votes reversed. Coved crown molding was popular close to the turn of the last century and in higher end homes. Some forms are made with ribs and some with veneer to create the shape. – Ed Beal Jan 25 at 14:26

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