During the weekend I’ve made a large (1 m in diameter) fireplace encircled with stones next to the furnace building site. I have spread a 5 cm layer of ore on the ground inside the fireplace to prevent the roasted ore from beeing mixed with dirt when it is dug out. I also got a really cheap second-hand 650 Watt Makita drilling machine with a mixer. It does a decent job turning wet bricks and sand into soft furnace clay mixture. The ratio is 5 or 6 bricks (about 4.4 kg each, including water) to one bucket of fine, white sand. I’ve decided to leave out the horse manure, partly because there’s no evidence of any kind of fibre in prehistoric furnace findings, partly out of plane curiosity. As opposed to most of my earlier experiments I now have the time to let the furnace dry out in a natural, slow pace. The dry, sunny spring weather is perfect for the job. This should minimize the amount of cracks, making the addition of fibre obsolete.
(Also, I’m still having a little trouble with my photo album plugin, so I might have to delete everything and start over…)