3. Framing the Hearth
Overview
Your oven sits on a two-layer hearth, comprised of an
insulating layer that rests directly under the oven cooking
floor, and a structural layer that hold the oven in place. The
insulating layer stops heat from leaving the oven through
the cooking floor, and is made from either 2” ceramic fiber
insulating board (FB Board), or 3
¾
” or 4” of insulating
concrete (vermiculite or perlite mixed with Portland cement).
The structural layer is comprised of either 3
½
“ of rebar
reinforced concrete, or a fabricated metal tray.
This drawing shows an FB Board hearth design.
A significant decrease in the cost of FB Board make it the
recommended installation option. Ceramic fiber board is
more efficient than insulating concrete, it is much easier to
install, and is priced very similarly to vermiculite concrete.
The Forno Bravo Pompeii Oven Kit includes FB Board.
For FB Board installations, the structural concrete layer can
be poured in a form built from 2”
×
4” lumber (38
×
235 mm)
and either 3/4" plywood or concrete board to form the
bottom of the hearth.
For installations that will use vermiculite concrete for
insulation, the structural concrete and insulating concrete
are poured in two layers in a single form built from 2”
×
8”
lumber (38
×
235 mm) and either 3/4" plywood or concrete
board to form the bottom of the hearth.
Thermocouples
If you are planning on using one or more thermocouples in
the hearth and/or cooking floor, you need to add them now.
You can either include the actual thermocouple wire in the
hearth when the concrete is poured, or you can use a straw
to create a chamber where you will run the thermocouple
wire later. (See Photo 3.4)
Instructions
The hearth form consists of a bottom tray and the frame
sides, which will hold the concrete hearth as it is poured.
After the hearth has cured, the form is removed (and
usually becomes part of the first fires that will cure your
oven).
Support for the Tray
First, using 2 "x 4" lumber set on its side, build the frame for
the bottom of the form. The frame should be roughly 3/8"
smaller than the opening of your block stand, so that it can
be easily removed after the hearth has cured. (Photo 3.1)
Next, cut (12) lengths of 2"x4" that will serve as the legs
that hold the bottom frame in place inside the stand
opening. You will use 1/4" shims to accurately set the top of
the frame. The top of the 2”x4” frame should be about 1"
below the top of the stand (to allow for the 3/4" plywood and
shims). Measure and cut your 2”x4” legs accordingly --
stand height, minus 2 1/2" (1 1/2" for the 2”x4” and 1" for
the plywood and shim).
Pompeii Oven Instructions
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Ver. 2.0
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