Sorry. Castable is my boom! It won't last.
I started to apply the insulating layer to the arch today. I decided to mix and apply it one five-gallon bucket at at time, because bashing up soft brick is killing my neck and back, and I just can't do all that I need without interruption.
I started out intending for the crushed softbrick particles to be about the size of coarse grog, but quickly settled for a gravel-sized bits instead, when I saw how dreary and, eventually, painful the task of crushing brick was going to be.
They only sell Portland Cement in 94-lb bags. 94 pounds!! Come on. While there are lots of people who can easily lift 94 pounds, there are lots more who can't. I can lift 94 pounds, but, ya know -- I don't want to. I'm going to grunt, and stumble, and possibly lose my grip on the bag, and have to heave it to get it in place, and my back will hurt the next day. Whoever decided that 94 pounds is the optimal package weight in which to sell portland cement was obviously not thinking of women, but not just that -- there are lots of men who would have trouble, too. The entire lot was only $9, which I suppose is great if you need lots and lots of it, but really, who needs that much? I mean, besides almost everybody who buys portland cement. But what about all those -- I don't know -- hobby masons? They must get stuck with loads of extra cement. Me, I would have gladly paid $9 for 40 pounds of it, which I can easily lift. And now I am going to have to figure out what to do with the leftover. Which is going to mean lifting most of it, as I only need a few pounds.
Oh, and I am sure you already know this, but portland cement and concrete (which is conveniently sold in bags weighing as little as 25 pounds) are not the same thing. Concrete has little rocks and other crap in it, which we don't want, as we are going to add our own little rocks and other crap in the form of crushed brick and Hawthorn Bond. Cement is also not to be confused with plaster of paris, but that is a story for another day.
Anyway. I mixed up a five-gallon bucket using parts-by-volume, 12 pts crushed brick, 7 pts Hawthorn Bond, I pt Portland Cement, 2 pts water. I applied it with a trowel to the west side of the arch, and will finish tomorrow. I certianly hope I am doing this right, as it is a sort of leap of faith -- if I've got it wrong, I'll probably eff up the work I've been doing for months now.
Either way, I'll let you know.