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Old 07-26-2014, 12:44 AM
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Thumbs up Re: Can I use clay paving bricks for my dome?

To a certain degree David, I agree with you, but with the thermal shock on a lower fired brick/paver and a more absorbent material (although minimal) the more proned to is to suffer from surface breakdown and drop small brick particles. My experience over the years is to see that clinker bricks (those receiving the maximum heat from the firing process with in the kiln) stands up to regular heating/cooling in an open fireplace than the lower fired samples. This is also seen in "low fired bricks" that fret away over the years with weather conditions only, no fire nor heat to accelerate the process. I have been down to Russel's Pizza Restaurant, observed carefully his 2 ovens and they work exceptionally well at a fraction of fire bricks.
I also agree that ire bricks are the preferred build material, but to build with the best alternative or not to build at all, that is the question!
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Old 07-26-2014, 04:31 AM
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Default Re: Can I use clay paving bricks for my dome?

http://www.fornobravo.com/forum/f6/b...t=Budget+build (Budget Build 36")

G'day
The link above is a pressed clay paver build.
What I would like to point out is that he used the " hit with a hammer " test and bypassed some possible bricks. Unfortunately it came out out the end that he was using a sledge hammer and a solid cement surface underneath. What can you say If you do apply this type if test to a brick a soft under surface like a bit of grass covered surface....I recon I could powder a firebrick easy the same way.
A lot of secound hand brick is not suitable just for the fact that 9 times out of 10 it's stored out of site out of mind at the back of a shed. Soaking up water covered in moss.... Certainly deteriorates them.
With a New pressed fired paver at least you have product that hasn't suffered from the elements.
In Brisbane for anyone that's interested.
There is Clapave in Dimore (Ipswich) they make a 29 per cent fire brick. They also produce a white fired brick common. Their pressed clay pavers are fired to 1200C.
Warrick on the Darling Downs they make a brick common that is reputed to weigh more than a Dinmore firebrick. Personally I have never laid my eyes on one of these monsters. So if you use these please tell me.
Recycled . There is one that stands out. Its a light red brick brick common used in the 50s 60s on a lot of the public buildings. An example for those who care to look is the C of E church in Wynnum. My diriveway is paved with these but of course I would not use now as 16 years in the ground.. Perhaps not.
My own oven dome is built of "light duty firebrick" the rest a mix of whatever I could lay my hands on.
If I was to build again... First I would build... Hey its a lot of fun .. And you get to eat from the results..
Secound i would build with whatever I could... A budget build.... A hearth floor of firebrick splits and a dome of Fired ClayPavers.. If I won Lotto .. That builder would be kept busy with instructions
As always
Regards dave
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Old 07-26-2014, 07:12 AM
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Default Re: Can I use clay paving bricks for my dome?

Yes Dave you are correct. A fire brick is generally far easier to break up (weaker) than a solid house brick.The reason is that the house brick is partly vitrified but the firebrick far less so because it contains less fluxes that help the silica start to turn to glass. It is the composition of the clay body that gives it the thermal shock characteristics rather than its raw strength. That is why I question the efficacy of banging a brick with a hammer to test its thermal shock characteristics. Taking this a step further, an insulating fire brick has even better thermal shock characteristics than a dense firebrick, but will crumble really easily if hit with a hammer.
African and South American low fired pottery (around 600 C) can be placed directly on a stove. While similar stoneware fired(1200 C+) pottery won't cope.You won't find any commercial bricks fired that low, because as they are designed for houses they want them to be partly vitrified so they are partly waterproof, but still a bit porous. It is the thermal shock characteristics that are important for our ovens and the firebrick is the logical solution. Most solid house bricks should be fine,
but some will not be and you won't be able to tell by smashing them.

Last edited by david s; 07-26-2014 at 07:22 AM.
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Old 07-26-2014, 07:22 AM
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Default Re: Can I use clay paving bricks for my dome?

hey Dave

I will let you know what happens to a Claypave paver yes fired to what you said 1200c I will be getting it re-fired once I play a little.

Fingers are crossed
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Old 07-26-2014, 07:25 AM
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Default Re: Can I use clay paving bricks for my dome?

If it is a clay paver why are you refiring it? It should already have been fired, most bricks to around 1100 C
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Old 07-27-2014, 04:34 AM
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Default 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
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Old 07-27-2014, 12:32 PM
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Default Re: Can I use clay paving bricks for my dome?

Nothing will happen to it.
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Old 07-27-2014, 02:53 PM
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Default 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.

Last edited by david s; 07-27-2014 at 02:58 PM.
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Old 07-27-2014, 11:11 PM
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Default 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.

Last edited by wotavidone; 07-27-2014 at 11:23 PM.
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