3.4. Plywood set in place.
The Side Forms
Next, build the sides of the form using 2”x4” or 2”x8" lumber
(depending on the type of insulation you are using) to fit
around the block stand edges. This frame forms the sides of
your 3 1/2” or 7 1/2 " insulating hearth. Set the boards at the
top of the outer edge of the block wall, and support them
with 2”x4” legs and shims similar to the tray. Check for level.
(Photo 3.4).
3.5 Form sides held in place with 2”x4”’s.
Rebar
Build a grid using 1/2” rebar on 12” centers. The rebar
should stop a few inches short of the form side, and it
should be supported at the mid-point of the concrete hearth
(roughly 1 3/4”). Tie the rebar intersections tightly with rebar
wire. The rebar should remain in the middle of the heath
and not be exposed at the ends during the concrete pour.
3.6 Ready to pour.
Tips and Hints
Cut your frame and plywood for the bottom of the hearth
form about 3/8" shorter than the actual opening. The
concrete will not escape when you pour, and it will be easier
to remove the form when your hearth has cured.
Use shims to set the bottom form level with the top of the
block stand. It will be easier to make the form level with the
top of the stand, and it is easier to remove it when the
hearth has cured.
To stop the top form from bulging out under the weight of
the concrete, use either (2) 2"x4"'s nailed in place on the
top of the form in one direction, and nailed in place and
angled to the ground in the other direction.
Alternatives
Island Hearth
Some builders want use their oven for baking multiple
batches of bread from a single firing. In this application a
little extra thermal mass in the floor will allow longer cooking
times at elevated temperature. This can be accomplished
Pompeii Oven Instructions
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