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Two years ago I built an experimental oven for the children of our parish Želimlje who had "oratorium" for 2 weeks immediately after the end of the school year.
The building material were regular red bricks and instead of refractory mortar I used a mixture of sand and clay (3:1). I finished the oven in about 2 hours and fired it immediately.
The oven was a great success and children really loved it - they baked over 200 pizzas in one week. Now they build the oven by themselves each year from the scratch what is a big project for them. Of course, they are quite dirty from the clay at the end, but who cares. It is important that they are busy with educational work and have no time to stick around and do stupid things which they would regret later. And what is also very important, they all have a great time as they all love eating pizzas, especially when they have to prepare them by themselves and can choose the toppings.
This kind of a approach can be used by anybody - building such a temporary oven in his back yard and keeping the children busy and happy.And it is easy to remove it and build it again.