materials

[Chris Bowman]

A few questions about materials:

1. Vermiculite versus Perlite: is one better than the other?
2. If using Vermiculite, what granule size is best for (1) lightweight concrete, (2) mortar and (3) loose insulation between the dome and outside structure?
3. If using self mix mortar does it matter what type of sand is used?
4. Most fire bricks I've seen advertised are 42% alumina: is this OK for floor and dome?
5. If using regular clay bricks rather than fir bricks for dome, what mortar mix should be used?

Thanks, in advance, for any replies.

Chris Bowman (in the UK)

[brickie in oz]

Do a search on the forums, its all been done before.
Here is the first question search results I came up with so no doubt the rest have been answered before too.

http://www.fornobravo.com/forum/f6/v...lend-5932.html (Vermiculite vs. Perlite vs. blend)

[dmun]

1. Vermiculite versus Perlite: is one better than the other?

No.

2. If using Vermiculite, what granule size is best for (1) lightweight concrete,...and (3) loose insulation between the dome and outside structure?

Unlike some categories of human endeavor, size doesn't matter.

(2) mortar

Vermiculite/perlite isn't used in mortar.

4. Most fire bricks I've seen advertised are 42% alumina: is this OK for floor and dome?

At the temperatures that we run at, the alumina content isn't particularly important. Don't pay more for high alumina bricks.

5. If using regular clay bricks rather than fir bricks for dome, what mortar mix should be used?

For the best/cheapest mortar for dome construction, search for "homebrew mortar (Mortar Choice)"
Don't use plain clay bricks if you can at all avoid it. It's a ton of work to build a brick oven, and saving a few pennies may be short sighted.

[david s]

Vermiculite versus Perlite: is one better than the other?

I think there is some variation in the two materials depending where it comes from. I weighed a 100 L bag of vermiculite and it was 9.0 Kg and the same size bag of perlite was 7.5 Kg This is a significant difference. This perlite contains more air and therefore a better insulator.The perlite is a little dearer here and for preference I like to use vermiculite because it is a bit easier to mix and doesn't create irritating dust like perlite.
Check the thermal conductivity of the two materials.

[GianniFocaccia]

As a general rule, the bigger the joint, the bigger the grain of sand needed. Since smaller joints are desirable in an oven, this requires a smaller grain. For one who has a small inside joint with a large outside (ie: a triangular-jointed soldier joint) it has been recommended to employ two kinds of mortar. Tscarborough, in one of his FB posts here, describes building the optimum mortar using multiple grain sizes in a single mortar akin to filling a jar with golf balls, then marbles, then ball bearings.