Expand 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 a little 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 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

 

[Stevers]

The course of upright bricks is the arch at the top of the 'builders' opening', and it's that arch that should be holding up the front of the chimney breast. Everything below that arch and between the original brickwork at each side is infill. You'll need to put something (a pre-cast concrete lintel as it's not on display) across the top to hold up whatever infill is left after you've finished, but in my experience that amount of brickwork should stay in place while you're mortaring the lintel in. You could also cut a taper in those bricks to make a bit more room if push comes to shove. All the cast iron inserts that I have come across are fastened back direct to the brickwork, and then plastered in, so there's more plaster to come off yet for you to get a better view of what's there now.

In the unlikely event that this is going to be a working fireplace, you'll need to get the state of the flue checked and if it's OK, fill the void behind the insert. When I did that for our living room fireplace I was advised to use a cement/vermiculite mix topped with a cement render to form the flaunches. I'm sure I reduced the gaping void with some bricks first though, as I wouldn't have needed to buy any of the bricks used for that.