This is part 3 of How to build a free-form bread oven. Click here for bread oven principles, plans and construction recipes (part 1), how to build a bread-oven base (part 2), how to build a bread-oven dome (part 4), the final layers (part 5), make your own oven tools (part 6), or cooking in the oven (part 7).

The insulating layer in the floor

The floor of a bread oven is made of two layers.

The bottom layer is made of insulating material that reflects the heat back into the refractory layer. It also prevents heat loss down into the base.

The top layer, just below the fire, is made of refractory material that stores heat.

Some people use empty wine or beer bottles within the insulating layer of the floor. The air pockets in the bottles provide insulation.

I made mine simply by using a 1 to 1 pumice and vermiculite mix. Both these materials are light and insulating. Mix the following to an oatmeal consistency.

5 parts vermiculite and pumice

1 part sand

1 part cement

ALWAYS MOISTEN A DRY LAYER BEFORE ADDING ANOTHER 

Spread the insulating mix over the moistened base slab to a thickness of at least 100 mm.  Take handfuls of the mix (using rubber garden gloves) and pack them around the edge to form a natural looking link between the floor and the rocks (see the darker wet mix to the right pf the picture).

Spread some aluminium foil over the base to within 5o mm of the outside edge of the base. Hold it in place with handfuls of mix around the edge.

Allow all this to dry over night. Cover the whole with plastic if you fear rain.

The refractory layer

The refractory mix is:

1 part cement

1 part fire clay

2 parts hydrated lime

9 parts sharp sand

Mix this carefully. It is essential that there are no lumps of lime within the mix. Mixing the lime to a paste beforehand is a good idea.

Spread the refractory mix over the floor to within 100 mm of the edge. (This 100 mm will later be filled by the dome’s insulating layer.) You could make the whole floor layer with this mix to a depth of 100 mm.  Make it level and smooth it off with a trowel, because this will be the working floor you slide your food onto. Before it dries, mark on the outline of the circles of the inner dome layer using the real-size plan or the knotted string. Etch a criss-cross, rough pattern into this area. With handfuls of the refractory mix build a low wall around this circle. Leave the surface rough (as in the photo below). This is the beginning of the dome wall. Leave it to dry before building the dome.

I chose to use fire slabs for the floor. They are laid on top of a wet 50 mm refractory mix layer. I used 10 fire slabs, 270 mm x 270 mm x 40 mm as in the design below left. I drew the floor plan onto the slabs once they were laid. Then I held the slabs more securely with a ring of refractory material (i.e. the first layer of the inner layer of the dome), still leaving 100 mm around the edge for the insulating layer.

Leave all this to dry over night.

To Build the dome, click here.

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