Re: 42" in Portland OR
The fireclay is in the mix to provide strength after the oven is fired. Something about the lime and concrete breaking down in the heat over time, IIRC - I think the fireclay is what provides the strength long term. I don't know that it's really going to change the characteristics of how the mortar dries. Seems like the sand is what should keep it from shrinking but I'm really just guessing.
The arch looks good, but I can see you're going to have a fun time tying your dome bricks into the back of it. You might try using your IT to scribe a line into the back of the arch bricks to figure out where they should meet each ring of your dome, and then use a grinder to shape the back of the arch bricks. The approach with an axed arch like you're building is a little different than what you do with a true arch - but if you look around there are pictures to guide. I'll see if I can dig one up
The fireclay is in the mix to provide strength after the oven is fired. Something about the lime and concrete breaking down in the heat over time, IIRC - I think the fireclay is what provides the strength long term. I don't know that it's really going to change the characteristics of how the mortar dries. Seems like the sand is what should keep it from shrinking but I'm really just guessing.
The arch looks good, but I can see you're going to have a fun time tying your dome bricks into the back of it. You might try using your IT to scribe a line into the back of the arch bricks to figure out where they should meet each ring of your dome, and then use a grinder to shape the back of the arch bricks. The approach with an axed arch like you're building is a little different than what you do with a true arch - but if you look around there are pictures to guide. I'll see if I can dig one up
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