Newbie needs advice for fireplace arch

Alex Hunter

New Member

I’m new here :)

I’m currently drylining a chimney breast and builder’s opening (cement boarding the inside of the opening).

The fireplace/opening has a brick arch and I would like to retain this feature without having to square it off.

I’m drylining the face of the chimney breast and will shape the plasterboard sheets to the front face of the arch. However I’m not sure how to finish the arch underneath? I’ve bought a plastic arch angle bead which I will attach onto the arch edge, but please can anyone offer advice on how to finish the arch return?

Bonding cost and then attach the corner bead and skim or use plasterboard scored width ways to create a slight curve, then skim?

Also is it ok to use plasterboard on the fireplace arch? Cement board would never bend!! Any other ways of doing it?

Any advice would be gratefully received.

Thanks Alex
Thanks for the sensible reply Jess!

Change of plan now; as I’ve lined the inside of the opening with hardiebacker I need to put a closure plate at the top of the opening. This means that I’d need to ensure that the plasterboard came down to meet this closure plate (which is square). So unfortunately it looks like I’m going to have to sacrifice the arch....

Also if I didn’t make sure the plasterboard on the chimney breast came lower than the arch you would be able to see the top of the cement board!

I’m trying to upload a picture of the said fireplace but it’s proving difficult. :mad:

For future reference Jess what would you use to render, I know it needs to be fireproof?

@Alex Hunter sand cement as standard. I had our bricky skin sides and build new arch on mine so the bricks gave a lip to board up to. Way easier and I love brickwork :)


  • IMG_0332.JPG
    1.5 MB · Views: 634
Small job but zombies right there’s more to doing this job , plasterers get paid for there knowledge and skill this is probably the most important part of that job , I’d definitely rip those boards back off , they shouldn’t be on there for sure
Tbf they look like cement boards which is correct...

But if not then yes defo would need to come off!
Plastic bead ?[/QUOTE
Oh Crap, I'm going to have to answer this, 'cos fitting stoves is my business right? I 'spose you've done it now but here goes;
So, anything in the chamber or close to it has to be fireproof, nothing else will meet Regs or be safe.

Forget anything with gypsum plaster in it, including pink board - B.Gypsum website is specific on what happens, I'm fed up with explaining it to builders.

Hardiebacker/Cement board is ok, could have gone higher but there is a fix. - The metal closure plate needs to be above the arch, make it with a large downstand edge on 3 sides that fills the gap down to the board, spray it black with the proper heatproof stove paint, not some cheapo from Halfords. Across the arch make it an upstand to support the edge.
If you can, drill and plug it to the back of the arch, great, but usually they're broken half bricks and will come loose. (refix with mortar). otherwise, leave it & just fill the gap with cheap-as-chips fire cement - lots, with a backing of mineral wool insulation torn-off and jammed in so that the fire cement can get a key.
The arch/sides is usually the hottest point - directly or very close to the stove; Lime cement render, plus metal mesh/bead if you can't get a key. Standard cement render tends to crack but try it if you want. You could keep the exposed brick arch by using a 12mm curved metal stop bead on the wall around it, or rounding the render edge off.
The front face is more of a problem - lots of installers get away with multishite, but, the recommended method is lime render again, proper old school, to a height above where the register closure plate is inside. Alternatively you can use the proper fire cement "Plaster" (it aint gypsum) & render from Vitcas. It's a bit pricey but works, you could also have used it in the fireplace chamber instead of boards.

You mention plasterboard externally to hide the arch - it will fail now or later, later is worse - it will crumble inside leaving a nice piece of fluffy paper to catch light. If you are lucky it will char first and fall down. Chop a chunk out and use Hardie backer and a cement render skim. Don't put it on wood battens as several morons have done on my jobs. Plaster will blow off - the voice of experience here.
You are of course going to put a new fireproof hearth in there extending at least 9 inches in front of the stove aren't you ? That type of stove gets hot underneath, don't leave anything flamable or meltable underneath the hearth, it acts as a cooker hotplate.

Talking of which, its just over 35 degrees in here, time to find a beer.