Industrial Fire bricks

[Marvellous_Matt]

I am building an oven in Alice Springs. I have just come across some fire bricks that are 115mm x 230, and tapered from 75mm to 70mm. Is there a way I can build a dome out of full bricks? If I do use the fire bricks do I still need to insulate the dome before rendering?
I am thinking about using vermicrete to cover the dome, but as there is no local supplier it is quite expensive to ship. How many 100l mags might I need to do the dome?
Many thanks

[david s]

Yes the bricks should be halved, they are too long to fit the circumference, particularly as you get higher and the Fabius decreases. You don’t say how big you intend to make your oven, but you can calculate the amount of vermiculite required if you know how thick you want your insulation layer to be, by using the formula for volume of a sphere (4/3 x pi x r3). Calculate the volume using the outside radius then deduct the inside volume using the inside radius. Remember to halve the result because it’s a hemisphere not a sphere. You also need to add 20% because there is a reduction of volume on mixing with the cement and water. If I were in you situation regarding high freight costs i’d Be using chopped straw/hay mixed with just enough slip (clay and water mix) to hold it together. Using crushed anthill for the clay should be readily available to you.

[Toomulla]

I used tapered bricks by choice the angle on the bricks in an arch is in fact constant, so by halving the bricks and using the taper in the horizontal you can achieve very tight horizontal joints. I laid the bricks out on a flat surface using a 1.5 mm spacer and determined the optimum diameter. If you wish you can cut the compound taper to the sides and achieve tight joints both ways

[Marvellous_Matt]

Thanks David, Anthills start a bit north of here but I might go for a drive and see what I can find. Would you recommend using a insulation cover over the bricks before the clay? Fire blanket or similar?
Toomulla what angle (or size bricks) did you have on the bricks you used for the arch? I was thinking that I could play around and try to get a nice arch, but think this angle will be to small.

I am also having trouble sourcing fire clay. I can get commercial rated fire mortar for about $30 a bag, someone had said they had trouble using it, it went off very quickly.

[david s]

Thanks David, Anthills start a bit north of here but I might go for a drive and see what I can find. Would you recommend using a insulation cover over the bricks before the clay? Fire blanket or similar?
Toomulla what angle (or size bricks) did you have on the bricks you used for the arch? I was thinking that I could play around and try to get a nice arch, but think this angle will be to small.

I am also having trouble sourcing fire clay. I can get commercial rated fire mortar for about $30 a bag, someone had said they had trouble using it, it went off very quickly.

A fire blanket is preferable, but you will still run into issues with freight.
Being in Alice it will probably cost you more in freight than the product itself. If no anthills around then you can simply dig for clay. There is usually a layer of it under the topsoil. Break it into lumps and pulverise it, then sieve it. The big advantage of using anthill is that the ants have already done the processing for you. This will also serve as the fireclay addition for the mortar. Commercial fire mortar does go off fast because it uses calcium aluminate cement. Most members of this site prefer the homebrew which proves superior to work with as well as being cheaper and is adequate for the temperatures we use.

[oasiscdm]

check out my build page 14 post 197 picture 4. i used various arch bricks to create a 1M internal dome with little mortar only used on outside to hold in place.

[Marvellous_Matt]

Thanks for your input. I decided to put my progress in its own thread.