Appendix 6. High Heat Mortar
Overview
A Forno Bravo modular oven, or a brick Pompeii Oven is
assembled with a high-heat, waterproof mortar. You have
two basic choices: FB Mortar, a commercially-produced
refractory mortar produced for Forno Bravo, or a mortar
that you mix at the building site, using locally sourced
materials. The site-mixed mortar can be made with
standard Portland cement.
The best solution is to use FB Mortar, or another pre-
mixed refractory mortar. Forno Bravo stocks FB Mortar in
California, and we highly recommend it. It is pre-mixed, so
you just have to add water. It sets hard, is easy to work
with, cures quickly, and is heat resistant to 1700F.
If you don't want to worry about shipping FB Mortar, or
want to save money, you can make your own mortar, using
either fireclay and Portland cement. Fireclay is heat-
resistant clay made up of aluminate and silica. When you
mix fireclay with Portland cement, sand and lime, you
create a product that is more heat resistant than basic
mason's mortar (Portland cement with sand and lime).
Measure your ingredients by volume (use a bucket or
shovel to measure), and mix only the amount you will us
within an hour or so.
Portland cement Fireclay Mortar Formula
•1 part Portland cement
•3 parts sand
•1 part lime
•1 part fireclay
Still, fireclay mortar is less heat resilient and thermally
conductive than a true refractory mortar.
Using FB Mortar
Mix the dry refractories to be sure that everything is well
distributed, and then add just enough cold water reach the
consistency of peanut butter. Mix the mortar mix and water
to fully incorporate the water and all the dry refractories.
Mix only what you need to use in small batches. You
cannot "re-hydrate" the mortar after you have mixed it the
first time.
It is important sure that you thoroughly soak your bricks
before applying any mortar, and that you keep the mortar
damp while it cures. You can spray the surface while you
are working, and cover the bricks and mortar with plastic
to allow the mortar to cure without drying out.
Pompeii Oven Instructions
© Forno Bravo, LLC 2007-2009. All Rights Served.
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