Two kinds of fire brick
Dense fire bricks are heavy refractory bricks. They soak up heat from the fire and release it back into the oven, which is what bakes the base of the pizza and keeps the oven hot between pizzas.
Insulating fire bricks are much lighter and full of tiny air pockets. They resist heat flow, so they are excellent insulation — but because they store so little heat, an oven lined with them on the inside would struggle to cook. Experienced builders on the Forno Bravo oven-building forum recommend dense bricks for the floor and dome, with insulating bricks used only on the outside or under the floor.
| Dense fire brick | Insulating fire brick | |
|---|---|---|
| Weight | Heavy | Very light (around 0.7 kg per litre) |
| Stores heat | Yes — the oven's heat battery | Very little |
| Insulates | Poorly | Very well |
| Strength | Hard-wearing; takes peels and logs | Soft; damaged by tools and wood |
| Where it goes | Cooking floor and inside of the dome | Outside the dome or under the floor, as insulation |
Why not ordinary bricks?
Ordinary clay building bricks are not made for repeated heating to several hundred degrees and cooling again. In the hot part of an oven they can crack and spall (flake). Fire bricks are made from refractory clays for exactly this duty. Ordinary bricks are fine for the stand and the outer decorative enclosure.
Laying the cooking floor
Floor bricks are usually laid flat, tight against each other, on a thin, level bed over the insulated hearth — without mortar between them, so they can be replaced individually. Keep sand and grit out of the joints and make the surface as flat as possible so the pizza peel does not catch, as Forno Bravo's cooking-surface notes explain.
A thicker floor (bricks on edge) holds more heat for longer baking sessions but takes longer and more fuel to heat; bricks laid flat heat up faster. A herringbone pattern helps the peel slide across the joints.
Building the dome
Domes are commonly built from fire bricks cut in half and laid in rings, each bonded with a thin joint of refractory mortar. Ordinary mortar breaks down under oven heat. Over the finished dome goes a thick ceramic fibre blanket layer, then the outer render or enclosure.
Cutting fire bricks safely
Builders use a wet brick saw or an angle grinder with a diamond blade. Always wear eye protection and a proper dust mask or respirator: brick dust is harmful to breathe. Curves are cut as a series of short straight cuts.
How many bricks?
It depends on the floor size, dome size and shape, and brick size. Send us the internal dimensions (or a drawing) and we will estimate the bricks, mortar, insulation and seal you need — see material selection advice.
Fire brick questions
Can I use insulating fire bricks for the oven floor?
Not for the cooking surface. They store too little heat and are soft. Use dense fire bricks for the floor and inside of the dome, and insulating materials underneath and outside.
Should the floor bricks be mortared together?
Floor bricks are usually laid tight without mortar between them on a thin, level bed, so the surface stays flat and bricks can be replaced individually.
What protective equipment do I need for cutting fire bricks?
Eye protection and a proper dust mask or respirator, as brick dust is harmful to breathe. Hearing protection is also sensible with power saws.
