Forge Build: insulation and clay
Last time we talked about building the main forge body, the frame of the forge. Now it's time to work on the interior.
The overall principle for the interior is that the end goal is, of course, to contain the heat pumped out by the torch.
Given that, many people build their forge entirely using bricks for the interior. This is a very good way to do it. For small-scale bladesmiths, a circular interior and small size is optimal, as opposed to blacksmiths who need to simply blast a ton of heat onto thick steel. We don't need all that much, but we do need efficiency in a small space.
Thus, most bladesmiths build a forge using high-temp ceramic wool insulation. That's what I used for this build.
I ordered Kaowool (this one, to be precise) off Amazon, a little more than I needed, for under $50. A friend of mine, Will Freeman, sent me some satanite clay to line the forge (we'll get to that in a minute).
Ceramic wool is an insulating blanket, it helps keep the heat contained and keeps the frame from overheating. I'm writing this article post-completion, and have used the forge many times. So far, the outside of the forge has not exceeded 400 degrees Fahrenheit, so it does a good job.
Note: Ceramic wool is made of ceramic fibers, which guess what: NOT HEALTHY for your lungs. Wear a respirator when working it. I suited up with glasses, hoodie, and gloves too; fibers stick in your skin like cactus if you're not careful.
I've only ordered ceramic blanket twice, and both times it came with a simple box cutter to cut it with. This works just fine.
It took a little bit of planning, but I got the wool cut to the right length, rolled it up, and cut a hole in the center to fit the torch flare. Because the blanket is a few inches thick, the tip of the flare and the interior surface of the blanket ended up flush, which is excellent because if the torch extended into the forge, it would overheat too easily and degrade much faster.
I placed it so the seam ended up at the bottom of the forge. Later on I'm planning on putting some firebricks on the bottom, especially if I intend to use the forge for forge welding: flux from this process dissolves (for lack of a better word) the forge lining. In any case, potential issues with insulation coming apart down the road are far easier if the seam is on the bottom, than on the sides or top where the edges could fall in.
Once the roll was in place, I trimmed it to be flush with the edges of the forge body.
The doors were a bit trickier, and took some creative cutting to fit the wool in just right, but I got it eventually. The basic idea was cutting a disc (or a bagel, for the front) for the back, then cutting a strip to line the edge just like the main body of the forge. The main thing is to make sure you have as few separate pieces of blanket as possible,just so there aren't weird gaps between pieces, and so that it's structurally sound.
Once the inside was completely lined with insulator, it was time to coat it with refractory mortar. Refractory is a type of high-temp clay, and ceramic wool needs to be coated so the fibers don't get in your lungs.
Now, uncoated wool is a long-term health problem. You won't notice anything immediately if you use an uncoated forge a few times, but the fibers will build up in your lungs.
Coating the wool with refractory both keeps it safe to use, but also keep the interior sturdy and in place. The refractory I used is called Satanite, and can be attained from a few different suppliers. On a side note, satanite is also one of the more common clays used for clay quenching, so it's worth getting a good amount. Rutlands, a common clay that's also widely used for quenching, falls apart a little too easily to coat a forge, so I would stay away from it for that purpose.
I'm not sure the exact water to clay ratio, but the goal is a sour cream like consistency. I just mixed in bit after bit till I got what I liked. You don't need anything in particular to coat it with; I just put on disposable gloves and slathered it on by hand. The clay doesn't have to be particularly thick; I did just one coat, and put it a little thicker at the insulator's seams.
Side note: because I had gloves on and they were covered with clay, I wasn't able to get any photos of this process, but it's pretty self explanatory
I also packed extra around the mouth of the torch, for extra security and structure.
At this point we're pretty much done. It's best to wait at least overnight for the clay to dry, and though it was still slightly damp the next day I fired up the forge anyway with no issues. It works like a dream: gets up to heat in no time, the doors swivel perfectly, and the amount of flame is perfectly variable!
You'll notice that I've saved one of the more important parts of this build for last: the torch, which will be next week. I planned on publishing that article much sooner, but due to it being a little more particular and with smaller room for error than the other parts, it's taking longer to write, so bear with me. I should be able to get it done by next week.