Barrel vault

[wolfy01]

Hi guys I'm doing my first oven at the moment and I'm up to my slab at present , question I have is would a layer of old handmade brick straight over the top of firebrick be sufficient ie 9" or do I have to insulate inbetween somehow?? Many thanks

[oblertone]

Hello Wolfy, it's a little difficult to answer your question without further information, but the basic principles of WFO building might help.

You are building a box to hold fire irrespective of the shape.
The box should be made from material that will absorb and release heat generated by the fire.
To stop the heat leaching out of the box it needs to be insulated, most importantly underneath.

The variables start when you determine what materials you are going to use; ceramic fire bricks are the 'gold' standard, but lots of other materials an be used such as solid bricks, heater blocks or clay. As you've mentioned old bricks I'm assuming these will form part of your build, these are best used as half bricks end-on to give you a structure about 4" thick. They can also be used on the floor laid long side up to give a similar thickness floor; the only downside would be lots of joints making an uneven floor but a herringbone pattern can alleviate the issue with slanted joints.

Placing bricks end-on to give a 9" thick floor would not only create more joints but take an age to heat through giving you a cool floor, which is not good. I like heater blocks which are about 9" square and 2" thick so you get less joints and good heat retention, but again there must be a heat barrier under whatever floor you use, otherwise the heat will just disappear into your structure.

Hope this helps, but please feel free to ask further questions and remember that pictures help enormously!