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Winter_Stomach_5540 OP t1_itc24lh wrote

Reply to comment by WolfKnifeLaserTorch in Second opinion - knocking out old fireplace (pic in text) by Winter_Stomach_5540

Very much obliged to you dear user, thats a really handy link

Very reassuring in terms of what I’m looking at already. A bit more work and I should have the info I need to continue - there is a steel form below the more recent brickwork, but I haven’t been able to locate an older form yet

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Hagenaar t1_itc6t0h wrote

Well laid arches are strong structures on their own.

It seems pretty clear the original arch was done without steel support. Obviously, most stone or brick arches throughout history were done this way. Steel support was a way provide a bit of insurance in case something failed - and possibly a crutch used by someone not doing their best work.

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WolfKnifeLaserTorch t1_itc8aks wrote

I don't think the original was made with a steel form. In fact, I think the lower arch is working as the form for the upper arch.

Remember that the force on an arch is going outwardly, not downwardly (like with the newer horizontal brick).

The top arch is doing most of the heavy lifting as far as supporting weight. It only needs help keeping the joints on its underside from pulling apart (outwardly force). This is where a steel form comes in, or in this case, the second arch.

The second arch is doing the job of a steel form by keeping the underside of the top arch from spreading. It also likely isn't supporting much weight. You should be fine with no support under the second arch as long as the mortar joints are strong on the underside and at the edges.

EDIT: I should note, I am not a mason, but my dad was. It couldn't hurt to get the opinion of a professional mason before you start pulling bricks.

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