The Portland Community College media crew was filming in the Rock Creek Learning Garden during Earth Week and caught the Alternative Building Methods class at work on the kiosk we are building. Watch the video, we show up at 0:25.
I have recently received several questions about the possibility of building earthen ovens so that they can be moved. Such an approach could make sense if you are renting your home or see a move in your future. Let me offer a few thoughts on the topic. Yes, earthen ovens can be moved, where there is a will there is a way. So let’s look at the issues.
Wood fired earthen ovens are heavy. An insulated oven with a hearth diameter of 24” weighs something on the order of 800 lbs. even when weight saving measures are taken. Earthen ovens are retained heat ovens and it is the mass that retains the heat. Building a lighter oven results in an oven that won’t hold as much heat.
Earthen masonry is relatively brittle. This makes it prone to damage from vibration and bumps. Yes, an earthen oven can be put on a trailer and hauled down the highway but this will shorten its life substantially. See Dan Wing's article on trailered earthen ovens. Ovens can also be built on heavy wooden frames which provide the base and structure to support the oven during use and transport.
A thousand pound oven can ride in the back of a pickup but the challenge is getting it into the truck. Methods one might consider are some sort of a sturdy cart on casters, or for rough ground a rugged sled that could be winched. A couple of stout beams placed under each edge of the oven’s wood frame would allow eight people to bear the load in the manner of a traditional litter. Or a fork lift would spare everyone’s back.
Another approach is to build a simple oven that is recyclable. There are festivals and events where an oven is built for temporary use, feeds many people, and is then dismantled, and the hearth bricks saved for the next iteration. Materials are then selected for their low cost and limited need of durability. Instead of using perlite for insulation use straw-clay, empty bottles, and sawdust-clay. Skip a durable brick door arch and just use a thin layer of plaster/cob to create the door opening.
This sort of oven won’t be as efficient but its temporary nature makes that less important. The embodied energy of such simple materials as clay soil, sand, straw, sawdust, a few firebricks, some old bottles and a wood door, is so low we can afford the beautiful utility of temporary.
When considering oven design, I encourage you to evaluate how good is good enough. How often will you be using the oven, fifty times in its life or 200? How long will it take you to move your half ton masterpiece to its new home? Do you have the skills and vehicle for this task or will you need to rent or borrow? Perhaps your time would be better spent with friends rebuilding your oven and backyard sculpture, what a great way to meet your new neighbors!