Hearth Floor Questions (More)

[SloW8]

Sorry, I know some of these are a bit redundant, but I am new and have a small brain. I plan on using 2x8's to make a form for my hearth.

1. If I put down 3.5" of concrete with rebar is that good enough for strength? (54"x54" square with a span of 42")

2. If I fill the rest of the form up with vermiculete, is that enough insulation?

3. Then I put my fire brick for the floor of the oven on top of the hearth. Can I use splits and lay them "flat" or do I need to lay them on edge to get enough mass for the floor?


T.I.A.

Joe

[kebwi]

2x8" are 7.5" wide. Assuming your frame overlaps the support wall by, say, two inches, you're look at 5.5" total fillable height. If you fill 3.5" of concrete that's only 2" of vermicrete. Vermicrete is a decent insulator at high thicknesses but it isn't all that great. It isn't like the fancy ceramic insulating materials. I doubt if 2" of vermicrete is much good at all frankly. I would recommend a minimum of 4" of rebar concrete (that's about what I did) and at least another four inches of vermicrete if you aren't planning on using any other form of floor insulation, more would be better.

Splits are not thick enough for an oven floor. Double them up to get normal face-up firebrick thickness, which is how most of us lay our floor. You could get three splits high if you wanted a little more thermal mass on the floor.