Enlarging fireplace opening

[dal3001]

Hi,

We've got a cast iron fireplace that consists of a surround and an insert. Our existing opening is slightly too small for me to get the insert into it and to get the surround flush with the chimney breast wall. I need to make it around 10cm higher and 10cm wider (5cm each side). The required width is more or less up to where I've knocked the plaster off in the picture.

Just looking for advice on how to do this really? I couldn't see any lintel from the inside of the opening, so I removed plaster from the chimney breast until I revealed what appears to be a brick arch lintel. Looking at the size of it, I'd say the original opening was wider so I'd be hoping it'd be OK to widen the opening as it exists now?

I've seen some people cutting a score in the brick with an angle grinder, or drilling a series of holes and then hitting along the line with a brick chisel but not sure of the correct approach in my case. The rear hearth that you can see (it sits higher than the front hearth) also needs to be removed ideally, so the whole hearth is the same level. It seems pretty tough and it's pretty tightly integrated with the brick of the chimney breast. Am I OK to remove this as well? I couldn't find anywhere else anyone mentioning a hearth slab being structural or key to the soundness of the chimney walls.

I've attached a picture of the opening as it is now and also of the fireplace insert/surround so it's clearer what I'm looking to do. Any input welcome! Also, just to add, I'm not intending to make this fireplace functional at this point in time.

Thanks


EDIT: If I could also ask for advice on patching up the chimney breast plasterwork after, that would be great. I've never plastered before but it seems like it's such a small amount to do, I wouldn't mind having a go myself. Plasterboard patch and then skim? Or Bonding instead? etc... Whatever is the easiest path really!

 

[23vc]

I’d try and carefully work the 2 courses of bricks that form the top of the opening out, and enough either side of them to get a 65mm concrete lintel in, with enough bearing (100mm ish) on each side to also cover the (widened) opening, without disturbing the stack of bricks above them too much. If the bricks above do drop, just crack on the fit the lintel then put them back in. The arch won’t move.
Once lintel is in, widen the sides as needed.
Check that it’s only that front skin of brick that needs supporting, and not the “gather” of the chimney where it starts corbelling in, as that makes things a bit trickier and may need extra little lintels going front to back.
Plastering - I’d do bonding and skim.

See pics of one I did (1) a load of bricks missing that dropped out (2) lintel in (3) bonding ready for skimming (wood burner in my case so a bigger, nicely squared opening)

 

[dal3001]

That's great, thanks.

So in this scenario, the lintel would just be keeping the rest of the non-critical infill in place I suppose? Just grabbed a concrete lintel today from Jewson that should mean I can crack on over the weekend with this Having had a look up the chimney, it seems this only going to be supporting the single skin of bricks that make up the chimney breast, the stepped bits of brickwork start a bit higher up than I'm looking to mess with.

 

[23vc]

the lintel would just be keeping the rest of the non-critical infill in place I suppose?

Yeah, and shoring things up if the arch is a bit ropey