Rebuilding fireplace brickwork

[inwood]

I'll get a photo sorted tomorrow but thought some initial advice from you all would help.

I have a fireplace opening upstairs that had been plasterboarded over (without an airbrick - Grrrr). After taking the plasterboard off I can see why it was simply covered. At some point there was a fireplace fitted to the brickwork but this has been removed (relatively recently as there are gypsum patches in the walls where the mantelpiece went). The throat of the fireplace has been built to match the removed fireplace. CO is happy for me to rebuild as it's in a VERY precarious state and then we're going to discuss whether to fit a reclaimed fireplace or leave simply as an opening.

Brickwork above the fireplace is single skin with earth mortar - again in poor state. I'm proposing therefore to support brickwork above as far as possible with strongboys and then remove and rebuild opening. The current arch is a soldier course on a flat fireplace iron (although this is completely loose). Soldiers lean away from center 'keystone' brick. 'Arch' ends are supported by stone walls (fireplace is built into corner of room).

Is this the best way to rebuild the arch or is there a better way anyone can think of? - e.g. temporary wooden former?

 

[chuckey]

A traditionel arch would have a significant radius to it, giving a rise of say 6" in the centre of a 4' opening. Often these bits of iron are used in victorian fire places. I reckon its so they don't have to wait for the brick arch's mortar to go off before they build the rest of the fire breast.
Once you have your basic former, if you nail on scraps of 2" X1", each of which sits under the centre of each brick, you can tart up the pointing under the bricks as well as the front.
Traditionally, each end of the former was sat on two wedges(pointing in opposite directions) which could be knocked out to drop the former. Just use a couple of pieces of wood with bits of thick plastic bag between them as a slip membrane.
Frank

 

[Gervase]

A form is easy enough to knock up - I had to replace the arch above a window last week, and this is what I did:

The wedges are at the bottom and the plastic sheet at the top to stop the mortar sticking to the form.

 

[shelli]

we did an arch with a plywood form - it wasn't hard to make the form

 

[inwood]

Thanks for the replies all, here's the photo:

As you can see it's in a bit of a state. If I replace the piers either side I can then probably fit a relatively flat arch similar to Gervase's. I suspect I'm going to lose some of the brickwork above since I doubt it will hold itself in place even with strongboys as the earth mortar is so loose. I'm surprised, given that it's only about 100 years old, that they used an earth mortar. I have a photo from about 1911 showing only the single stack which was built onto for this fireplace after that. Ye olde building control probably wasn't as strict then though.