I used the mold from the inside of the oven for the final arch out front, i had to cut a little of the sides as i did the double brick supporting walls which made that arch a couple of cm's thinner.
Then just supported it with bricks.
i laid the 2 side bricks with mortar but after that I just mortared the back of the brick where it hits the chimney and then spilt/pushed mortar down the gaps as there wasn't any space, kind of like "pointing" the bricks, then i just pushed mortar in the fron joints and took the mold away after 1 hour.
The arch stayed up and i was able to fill in any gaps with a kind of rendering technique.
