I’d found out that the Romans discovered a bread oven door should be 60-60.5% the height of the arch behind it, for a good draw for the fire. So I wanted to build the arch as a semi-circle built on two bricks, with a same size semi-circle door arch in front with no bricks raising it up.
Now was the time to use my schoolboy maths that had laid dormant for over 20 years! I wanted to work out how many bricks I would need for the arch if they were butted up against each other.
The circumference of a circle is 2πr where r is the radius of the circle. I only needed a semi-circle so and my diameter would be 70cm to give me space on a 122cm (48″) square base. So the the circumference was 110cm. Bricks measure 230x115x65mm and we would be using the lengthways and the 65mm edge butted against each other. So we would need 1100÷65=16.9 bricks. Each arch would need 23bricks, with another 17 for the doorway arch.
We made a wooden former out of some scrap wood, so we could build the three main arches all at once with some interleaving to give extra strength and because Pete is a brilliant brickie!
We could then place it on eight bricks to get it to the right height and central to the oven with space at the back for a back wall with insulation gap before the outer back wall.
The bricks were carefully butted together on the hot side with heat resistant mortar to bind them together. They were also interleaved for extra rigidty.
The back wall was built at the same time with a minimum of mortar…
The final header brick were cut to fit snugly with an angle grinder. Note the “safe” working practices of my mate Pete.
Once complete, we troweled on a layer of heat resistant mortar and then removed the former.
You really should buy this excellent book on making bread – you’ll understand the theory behind bread, ow to make a great pizza dough and all sorts of other breads you’ll be cooking soon in your oven!