Sunday, October 2, 2016

Before You Build a Brick Oven: A cautionary post

The desire for a wood-fired oven drives the market to create facsimiles (that is something that 'looks' like a brick oven but doesn't work like one).    It occurs in every other commodity; we buy something as simple as a pen or a fishing reel, an ice scraper, or a wheelbarrow and find that it is not built for the purpose for which we need it but for the purpose of being sold.
The reason why I am critical of this with regards to brick ovens is that these are both major investments and contain fire.  In my mind, a major investment should more than adequately compensate the buyer for his or her money spent. Something with fire needs to be safe.  For instance, my truck should run well past the date on which I pay it off and, incidentally, not blow up!

300 year-old Brick oven at Annaberg on St. John USVI, windmill in background

Whether you are building your own brick oven or having it built, attention to materials, both specifications and quality, should enter the equation.

1. Do the plans (or design) fit the traditional and technical standards for oven design?

2. Have the designers and builders taken into account the ergonomics of cooking in one?

3. Are the materials up to withstanding temperature extremes and fluctuations associated with wood-fired ovens?

4. Have the designers and/or builders satisfied the aesthetic potential or wishes of the user/buyer?

Take these one at a time:

1. Wood-fired ovens are thousands of years old.  The design was essentially worked out long ago.  The fire heats a mass, traditionally a dome, and exits the flue at the front.  If any plan or builder tells you that the chimney exits the center of the dome, WALK.
Although you will find ovens built as barrel vaults and sprung arches, they are not the best design.  They came along during the industrial age and require flat walls, front and back, that will eventually gap from expansion.  Sprung arches are contained by steel rods and channel iron; they will degrade long before the brick of the oven, causing the arch to fall.  I examined a very large sprung arch oven in Portsmouth NH this summer.  It was required to be replaced every ten years or so due to the roof sagging in.  Too soon!
Many pounds of beef slow-cooked (note 2 handled door)
Wood-fired ovens need to have a mouth that is no more than 60% the height of the oven vault.  If they are full height mouths, you have a fireplace, not an oven and it will not heat up.
Wood-fired ovens are intended to keep the heat in the oven.   Plans without insulation (or insufficient) under the floor or over the oven will not work well.

2.  The height of the floor of the oven should be at bent-elbow height (varies with user but often 40-44")
The user should be able to see all part of the oven interior.
Accommodations for working space should be made nearby.

3. Most wood-fired ovens are made from two materials: Fire brick or cast refractory concrete.  Fire brick ovens which I build have the advantage of having many joints (very small)  this distributed the expansion when hot.  Fire brick is also designed for the temps found in brick ovens.
Cast refractory concrete, whether made into a solid shell or in sections, needs to be reinforced in order to withstand the temperature swings and any other shock.  Sectional pieces can be damaged in shipping or assembly and fail later.  Cast domes are rarely fully half domes.  The point at which the wall straightens is its weakest point.  Still there are some very reputable products.

4.  All prefabricated ovens are made to look alike; they are the tract housing of wood-fired ovens.  Thousands are made; nothing special.  As I described in the 'competition' post on this blog, you can do better either yourself, or with an artisan mason.
These are ancient devices, unique to each town, castle, and hamlet.  Why wouldn't yours be as custom?

inexpensive cob oven being built
Cob oven in Costa Rica
I have also posted ways to build an oven for very little money.  This post is for the people who will be spending a chunk of  time or money or both.

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