As a mold for the inner chamber, I have used a piece of a paper tube of slightly bigger diameter than is my goal and a bottom made of plywood with supports that could hold the forge on its side like an impromptu bucket. I have covered the plywood and the tube with a plastic paper bag to make it waterproof. For the inlet-outlet channels, I have inserted into the orifices plastic tubes at an angle. Both tubes are at an identical angle, slightly inward and off-center. The idea is to create a rotating vortex of hot air in the forge since in the previous one I got the best results when I have managed to achieve this. Both channels should be approximately the same.
After that, I have mixed ordinary fireclay with pearlite at a ration 1:3 to the consistency of dry cement and stuffed the whole structure almost full, with only about 5-10 mm gap at the top (at the bottom the gap is taken care of by the thickness of the plywood. I think I have used too little binder (water glass) – I have used the amount recommended for the fireclay and I forgot that the dry pearlite will suck out most of it – so the result is not very strong and it is a bit crumbly. But I hope it won’t be a problem since it is not a load-bearing structure and I will make 5-10 mm hard coating on top after it dries. It did not crumble when I have carefully taken out the tubes and the plywood bottom after three days.
Now it will take its time to completely dry. Today it is over a week and still, it is very wet. I have added a fan to blow air through it to aid the process a bit, but even so, I suspect it will take at least a month to dry properly. Luckily I have twelve knife blades hardened and in work now, so I won’t need the forge for some time. Plus soon there will be more than enough work in the garden to keep me occupied for weeks.
So, in the meantime, we all can watch cement dry.