Will these bricks work for the dome/hearth

[yoboseyo]

Hi,

I'm researching red bricks to use for the dome/hearth as fire brick isn't available locally (I'm in Canberra, Australia). From my investigations, generally Australian sources say red clay brick is okay and standard, a sentiment less shared in other parts of the world. I'm not sure if our bricks are different at all.

However, I'm hopeless at telling which bricks are clay, fired, pressed. I have a few types and I'm hoping someone can help identify by looking at them

https://imgur.com/a/bmGFNmy

The first pictures are brick pavers from a driveway.

The next brick I'm not sure, but it's printed "Bulli 135 M"

The final pictures are what I'm pretty sure are pressed red brick (CB stands for Canberra Brick)

I've uploaded to here what I can (discarding some that don't fit the size requirements)


Paver


Unknown



Pressed Red

[david s]

you'll probably get away with using pressed reds for the dome, but not for the cooking floor.

[yoboseyo]

you'll probably get away with using pressed reds for the dome, but not for the cooking floor.

Do you know if the first 2 bricks are pressed reds?

[david s]

The first pic looks like a fired clay paver which I think are extruded and wire cut. The second pic look like fire bricks and the third and fourth look likepressed red house bricks. The method they are made by has no bearing on their suitability. Neither is the temperature to which they are fired, it’s the composition of the clay body that determines their suitability and you will have no idea of this by looking at a photo, striking the brick with a hammer or hitting it with a blowtorch.
To test whether they have been sintered ( fires in a kiln to turn the clay permanent), soak the brick and rub the surface. If it doesn’t turn to mud it’s sintered.
Generally you need dense bricks for both the dome and the floor. The denser the brick the higher is it’s thermal conductivity, but the harder they are to cut. They should be around 2 kg/litre. A quick measure, calculate volume and then weigh the brick will give you its density.

[yoboseyo]

They should be around 2 kg/litre. A quick measure, calculate volume and then weigh the brick will give you its density.

I did a quick measure and the density turns out to be:

Paver: 2140kg/L
Bulli brick: 2042kg/L
Canberra red: 1842kg/L but that includes the indentation. Maybe I could've submerged it and done a displacement test which would've tested sintering too but maybe next time.

So yea, seems like they are pretty solid. I don't really want to roll the dice though, without more tests.

[david s]

I think you mean g/litre

[yoboseyo]

I think you mean g/litre

yup, my mistake

[mefornaio]

As he said you could "probably" get away with the reds but in my opinion that's a big risk. Those bricks are very old and "probably" closer to would not last very long even in the dome.

I built a small barrel vault bread oven years ago out of standard reds (new ones) and it held up fine. If your going to try to sub out the fire bricks, which really isn't a great idea but if so use new red solids as a replacement.

There are some areas that are best built using proven materials for their application. Using fire brick for the dome and hearth is one of those.

It's worth the expenses in the long run.

[yoboseyo]

Those bricks are very old and "probably" closer to would not last very long even in the dome.

They are indeed very old bricks. Anywhere from 1930-1960. They come from a factory that apparently makes higher quality bricks than today, although I don't know what makes it so. I heard they are fired at high temperatures and "double pressed" and "double baked" (although I'm not sure what these terms mean). I can't imagine old being a bad thing - they are designed to last when houses are made from them.

[Delta]

Would the "Reds" be suitable for the Chimney?
I have lots of old reds from the front fence I pulled down and have run out of firebricks.
At $8 each here in Brisbane I am hesitant to built the chimney stack with fire bricks?
Cheers