Advice re the insulating hearth

[maver]

You only need to wait until the vermiculite cement is hard, which is about 3-7 days. I didn't use forms, unsure what your question about cutting it is (a jigsaw should work well, but I may be misunderstanding your question). I'm sure there are lots of clever forum members who have better ideas, but if you just support the base of the forms with bricks (just a few stacked against the foam) until the first few rings are up you ought to be able to remove the support bricks after the first few rings.

[Archena]

Yea!! Another Alabamian!!!

[BamaGirl]

Thanks for the quick reply. Today the hearth feels hard but I am going to give it a few days. I can't decide whether to use forms or not. It almost seems like it would more trouble than it is worth. I am sure I will have many more questions ( probably some stupid ones ). I just dont want to spend this much time and work in 102 degree weather and mess up.
Thanks again for your help.
Gardendale, Alabama

[Versachi]

I planned on using forms with my oven but I found it easier to work from inside my oven so that I could attempt to fit my joints as tight as possible. I made a template of the dome shape I had in mind and cut that in half leaving me with just a quarter piece which I used to check my angle every 4-5 brick or so. I think you will find that once you set the angle of the first brick in each row (especially the first 4-5 rows) that you can set all of the rest in that row on the same angle just using your eye if you are careful. Nice to have that quarter form though just to make sure you aren't getting too far off course.

Cheers, John

[maver]

I think the half dome form idea is a good one. It may be easier to make than the shims I used. With shims, you have to cut a different angle for each course. The quarter form could perhaps also be supported by stacked bricks on the oven floor to support the ends of the upper rings which can be a bit difficult to hold in place until each ring is finished as you are fighting gravity.

If the form had some heft to it you might even get away without having to reinforce it with bricks. Maybe you could make a plywood cradle for the lower part, that accepts a few bricks or even a half concrete block at the base, then sandwiches foam up top. After the build the foam culd be cut out or pulled out of the cradle, the wood could be burned if it did not fit out the oven opening, and the block could be pulled out the opening.

[BamaGirl]

It's been 3 days since I poured the hearth and it has cured quickly. I can stand on it today. I cut about 60 bricks in half this morning and started laying out my chains to get an idea of how it will look. Still have a lot more to cut. I am planning to lay the cooking floor later this week. The fireclay and sand is mixed wth water to make a paste. Correct? What is the consistency like?

[dmun]

Originally the fireclay and sand was mixed with water to a loose mortar consistancy, and trowled on the insulating concrete with a quarter inch notched trowel, like the kind you use for floor tiles. I believe the current thinking is that you can lay a thin dry layer of the mixture, lay your floor on top of it, so that if anything is a little high, you can pull out a brick and scoop out a little of the dry mixture. When you get your floor as flat and level as you want it, you wet the floor to solidify the base. Either way works, the second way is a little more forgiving of error.

[james]

I would agree with David. I have done the wet mixture, as well as notched trowel Refmix to attach the round floor pieces, and I think the dry mixture is easier in terms of getting the discrete bricks level.
James

[Hendo]

I'm curious about two issues:

1. What is the reasoning behind the recommendation of 50% sand with the fireclay? I used 100% dry fireclay, as I found the stuff flowed much better when I plonked a brick down, and in fact the sand seemed to inhibit this 'flow', which ultimately affected the level of each brick and left voids underneath it.
2. If using the material(s) dry, what is the purpose of wetting the floor after laying the bricks? Aren't we just trying to create a level cooking floor?

Paul.

[BamaGirl]

My hearth is unlevel in several places and I wondered which way would work the best. Thanks for all of your advice.