mortar that does not use Portland cement (which breaks
down under high temperature cycles) as a binder, and uses
refractory aggregates.
A lower-cost option is to mix a modified Portland cement
mortar, using fire clay, sand and lime. While the homemade
mortar will not be as durable as a true refractory mortar, the
addition of fire clay to the mix gives it improved heat
resistance compared to standard mortar and it is
inexpensive.
A third option option is to purchase a different brand of
refractory mortar from your local masonry supply store.
Finally, makes sure that you do not use a wet, premixed
fireplace mortar with water-soluble binder. There are a
number of mortar brands designed for in-door fireplace
installation, where the mortar does not cure to a fully-cured,
waterproof state. This is the wrong product for pizza oven
installation.
The Second Chain
Subsequent chains are made up of brick cut in half and set
on their wide edge (4 1/2") with the clean edge facing in.
The angle of the inward curve is set using a standard
wooden shim that you cut to the necessary angle. To
determine the angle of your oven's inward curve, and of the
shim itself, build a trial layout, and cut your shim accordingly
(Photo 7.4).
7.4. Cut your shims to match the trial dome layout.
Do not allow for an inside mortar joint, as you will be setting
the edges of the bricks facing inside the oven flush with
each other.
Before you mortar the bricks in place soak them in a bucket
of water. Firebricks are more porous than clay and will dry
out the applied mortar quickly if they are not moist. Cement
cures through a chemical process that creates heat. If the
surrounding moisture content is too low the mortar will cure
too quickly and will not have the proper mechanical
properties such as strength. Remember, you want cement
to cure, not dry out, so starting with wet bricks and keeping
completed masonry damp is a good thing.
Begin laying your bricks using high heat mortar. The bricks
will follow the angle and curvature set by the wood shim.
After the angle is held in place with mortar, remove the
shim; fill the open space created by the shim with mortar,
and move on (Photo 7.5).
7.5. Using a shim to shape the dome without forms.
Subsequent Courses
Stagger the brick joints, course to course, much like the
brick you see in block walls and brick houses (Photo 7.6).
There will be bricks in the first chain that line up with the
wall brick. This is normal. However, on the chains they
should all be offset.
Pompeii Oven Instructions
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