Slowly but surely making progress on the oven. Since we last spoke I glommed onto my neighbor’s concrete order to pour the bridge slab and fill the cells of the block wall. I helped him pour a sidewalk, and afterward the truck backed on up and turned what would have been hours upon hours of lugging bags of quickcrete around into a very short and simple process.
While the slab cured I got some of the rest of my materials: insulation, firebricks, and mortar. I measured and cut the insulation to match the footprint of the oven floor, and it turned out I had one entire sheet left over. Not wanting to have it sit in the basement indefinitely, I decided to add a second 2″ layer of insulation - that calcium silicate board surrounded by a moat of ‘vermicrete.’ That is a mixture of anywhere from 5:1 to 10:1 vermiculite and portland. Again, wanting more insulation, I went with 10:1. Weird stuff, especially if you’re used to concrete.
That set up fine, and I next laid the second layer of insulation board followed by my floor bricks, which had been roughly trimmed to match the oven footprint. I mixed together a 1:1 combination of fireclay (not to be confused with mortar!) and silica sand, and spread it out with a notched trowel under each layer to help get things level. Once the floor bricks were set, I used my little Makita polisher to grind out some of the high spots in the floor - firebricks are pretty far from consistently sized.
So now I have cut the first ’soldier’ course of bricks angled at the back to make for a smaller mortar joint, and also cut the first row of bricks above that into a trapezoid shape - again, less of the really expensive mortar, and more of the relatively cheap bricks.
I also fashioned an ‘indespensible tool’ which is basically some square tubing, a hinge, and a bracket. When you swivel that around on the hinge, the arm tells you the correct distance from the center as well as the angle to (in theory, anyway) build a perfectly dome-shaped dome. The black stuff is just a scrap of leftover siding from our house.
So now I wait for the right mortar…the stuff I originally got comes in a 15lb. pail and is ‘air set’ - meaning it gets hard when exposed to air. Unfortunately it is not designed for outdoor applications and won’t hold up over time to humidity. I’m trying to find anyone around to source the material from, and the two best options at this point ring in at $100 per 50lb. bag when you include shipping. That is about double the ‘real’ price, so I’m trying to figure out options.
