This may not be the fastest forge to build, but it was worth the time. These ingredients have been used on all my clayed forges. The secret is slowly curing and really rehydrating the kitty litter before hand:
A dirt cheap recipe for fire hardening clay in forges— Works great for projects big or small; I just winged it loosely off of some other recipes. This is an approximation. That was modified as I went along and needed more. I just went for something that “looked right”.. not that I knew what that was. I started off drier and got wetter to keep the large mass from cracking:
-1 20lb Bag kitty litter (the unscented bentonite clay kind) is barely covered with water in a wheel barrel.
-Add three full shovels of sifted red ground clay. (Sifting is really just a formality, but it should be done dry.. if it’s from a deep enough hole.. like a charcoal barrel pit then it’ll be well clumped and moist almost pure clay)
-Stir it all together and wait at least 24 hours. Occasionally stir to make yourself feel productive. =P This will soften the clay pellets as they absorb the water. Additional stirring will make sure all the mix stays wet. (The weather was mild, but cool at night when I did this so use less water in winter, and possibly more in summer)
– Once about half the standing water is soaked up or evaporated. Then add about equal parts wood ash and kitty litter to the mix until it’s to the desired consistency. For a single layer about an inch that’s something that clumps together in your hand without crumbling.
This mixture should to cure very slowly.
I would apply it in about one inch thick layers around firebricks letting them dry 24-48+ hours in between. I used a heater and halogen light at night because it was getting into the high low 60’s. I’d check on each layer to keep the outermost “skin” moist. The goal was to avoid lots of steam from the inside escaping and cracking a dry outside. After many layers were applied I waited maybe just over a week with 75-degree heat and air movement. Then I built a small wood fire in my new forge. I built it up to a nice sized fire taking up the whole forge over a few hours and then let it burn HOT for half an hour before letting it slowly cool.
This forge wasn’t a single afternoon project, but it’s served me for a long time now:
A tip with all clayed forges used with coal is to leave a thin layer of ash in the forge, or even apply a layer mixed with very little water. This will help prevent clinker from bonding with the clay. Instead it bonds with the ash.
Hardwood charcoal or bamboo charcoal are what I prefer to use n the trench forge. But coal can be used in a pinch.
Some relative information on clay:
Clay when used in bladesmithing for heat treatment.
I went on a quest to find out the science of how clay hardens… Instead I found debate!
I’ve been introduced to some new vocabulary that is very interesting: Sintering.