Can I use clay paving bricks for my dome?

[cobblerdave]

Re: Can I use clay paving bricks for my dome?

G'day
Colin's paver is outside his entranceway so the matter of temperature in his final prduct is not a concern.
My question is what happens to a firebrick when is taken above those 500C temps of a WFO to those 1200!C temps does it finally vitrify?
I'm an old school sailor and yes I've helped "repack a boiler" it's not a pretty task. And preferably done in harbour fully cold.
Regards dave

[Tscarborough]

Re: Can I use clay paving bricks for my dome?

Nothing will happen to it.

[david s]

Re: Can I use clay paving bricks for my dome?

The end point of vitrification is when the silica turns to glass and melts. Vitrification stars at around 1000 C and the clay body becomes progressively softer until it finally turns liquid. In a fire brick, because of the reduced amounts of fluxing materials this does not occur at working temperatures up to around 1500C, but much lower for red bricks which may be fully vitrified (made completely waterproof) at around 1200 C. I once completely melted a pot that was made from earthenware terracotta clay (plenty of flux from the iron oxide) when I glazed it with a stoneware glaze and fired it to stoneware temperature (1260 C). The whole pot turned liquid a wrecked the shelf on which it was sitting.The same thing occurred to a kiln I built with mud bricks as an experiment. The wares inside fired ok but the 3 to 4 mm surface of the mud bricks had melted off in sheets.

[wotavidone]

Re: Can I use clay paving bricks for my dome?

You can build a pretty decent oven with fired clay pavers.
The precautions I take are as follows:

Look for pavers that are fired all the way through. This might sound funny, but some pavers are black in the middle. They aren't very robust.

I look for ones that are one colour all the way through, and when you cut them with a wet saw you can see all the little bits of multicoloured grog surrounded by the monochrome new clay.

I test as follows - using a butane camping stove, one of those things that take an aerosol sized can of gas, I heat a half brick until it is at least 450C all over, as measured by my infrared gun. LPG doesn't burn anywhere near as hot.
I let it cool and drop it on to rocky ground from shoulder height. If the paver cracks, no good.
There is a remarkably wide range of strengths in clay pavers, take the time to sample all the available options.

Note that, the harder a paver is to cut, the worse it seems to fare in my little test. I reckon high fired bricks are brittle.

I try to find pressed pavers for the floor, pretty relaxed about using extruded wire cuts for the dome. Littlehampton Brick pavers worked in my first dome.

It helps to understand how pavers are coloured - quite often it is done by regulating the temperature to influence what oxides are formed.

So you might see a paver that has been fired quite hot to get a particular colour, but it might have been fired pretty quick so that the inside hasn't reached the temperature, only the surface 5 or 10 mm. These bricks are hard and coloured on the outside, black and brittle on the inside.
They don't work in my test, but have served well for a couple of years as the floor of the outer arch, where they only get to a couple of hundred C at most.
For the dome, IMO it is more about the brick being fired all the way through, rather than how hot.

I have measured and weighed quite a few pavers - they really are not as dense as firebrick, but it's not a huge difference.