Opening up a chimney breast

[Livi]

Hi all,
I know that some of this is discussed already here and elsewhere online but I've got a couple of questions I can't find the answer to.

In my 1900 Victorian terraced house I have a plastered chimney breast in the front room (second pic). By tapping on it I can hear that there's a boarded up small opening at the bottom. I would like to remove the board and chip away at the plaster to expose the recess. I don't want to put a fireplace in it, I just want to have it as a decorative opening as in the first picture attached. I would accept any size of opening and wouldn't be keen on messing with whatever lintel/brick arch is there in order to make it bigger. The hearth is still in place and looks like it has some pretty nice original tiles under some poured concrete (third pic).

I have the following questions:
- What are the best tools to use to tap off the plaster?
- Once the recess is opened, I want to ensure it's weather proof. I know this requires a cowl on top of the chimney stack, but I assume I'll need to close off the lower part of the chimney in a way which also enables ventilation - is this correct? I was thinking of just wedging some MDF, possibly with some insulation board, into the lowest part of the chimney that it would not be visible in to enable this. I'd drill a few small ventilation holes. I will post a photo of what I've got on top of the chimney stack soon.
- I plan to try and pry up the concrete on the hearth and expose the tiles, and do my best at cleaning them up. I think it would be nice to have the hearth slightly raised (about an inch or so in relation to the floorboards) - what is the best way to do this? I have a suspended timber floor underneath.

Any advice much appreciated. Thanks!

 

[ree]

Cut the paint seal & mitres with a knife, & then slowly prise the skirting board off.
Come in 125mm from both sides of the hearth and that center bit will be the fireplace opening.
Cut out a small panel 300mm wide x 450mm high of p/b with the knife.
Now you can hopefully see what needs removing to open up the fireplace.

After the fire place opening-up work then lift the sand & cement off the maroon tiles.
Lift out the maroon tiles to expose whatever's been used as a background.
Use a spatula type paint scraper to lift the s&c and the tiles.

Why not post photos when you've got this far?

 

[^woody^]

Padsaw if it's board.

Lump hammer and 2" bolster chisel for bonded plaster.

The flue is likely weatherproof now if there's no damp on the wall.

 

[Livi]

Thanks all - will post photos after I’ve done the first stage. Any ideas on a suitable vent which will provide some draught proofing too?

 

[Livi]

Ok I've removed enough plaster to realise there's a potential structural situation.
There is a brick arch at the top of what I think must be the original opening, with a 9" single skin brick column either side. Inside this presumably original opening is another single skin (seen here in more red-coloured bricks) which has it's own little opening, and this seems to be held up by a little steel rod functioning as a lintel.
The brickwork of the original arch is damaged and much of the mortar is perished, and although the bricks don't seem lose I woudn't trust it to hold up the chimney. I guess it has been ok because some of the load bearing is going through the new bricks and steel bar, and I wonder if at some point this was used as a bodge if there were signs of the arch failing.

I think I have two options: Install a lintel, or replace the bricks of the arch. The latter worries me because the mortar is so friable throughout the whole chimney. Could I get away with putting one or two steel rods on the underside of the arch, and if so how would I get one to fit the exact contour?