| Fire brick recipe?
Posted 9 Feb 11 2:56 AM
Hi all, im looking for a recipe for home made fire bricks.
I want to make some pizza ovens and fire places etc...
I am planning to make casts to set them in, the bricks will not be fired like normal bricks.
Im hoping that the temps of the fire place or oven will provide adequate curing temps once they are installed before insulation goes on.
They will be say 500mm x 500mm x100mm slabs for the flat surfaces and U shape casts with reinforcing for the roofs.
I am hoping to use a mix of glass (run in the concrete mixer to break it up)
clay and cement.
Just looking for a mix that will be fairly similar to fire bricks... the recipe is just an idea, can change if needed.
All sites on the net that have pizza ovens etc say "By some fire bricks"
I want to cast my own as they cost a fortune.
Cheers in advance : )
Posted 12 Feb 11 2:45 PM
Hello from a kiln builder and potter,
A kiln, fireplace and pizza oven run at different temperatures and construction is different accordingly. The oven would operate at less than 650oC, the fireplace at less than 1000oC and a potter's kiln at less than say 1350oC.
The bricks for each should be pre-fired to at least 150oC higher than their maximum operating temperature.
However a pizza oven can operate at less than 300oC and can be constructed with a concrete/perlite clay mix and be reinforced with mesh to avoid collapse. The reason why steel reinforcing cannot be used in any other type of higher firing fireplace/kiln is that the steel expands while the clay shrinks leaving the steel exposed to flame and ultimate destruction. Likewise glass melts at 700oC and is unreliable as a fluxing bonding element in a brick.
There is a sound reason why fire bricks are made to the common standard size of 9”x 4.5”x 3” (imperial) – any larger size will spall and crack in unwanted places, so your suggested sizes are definitely going to fail, Again the reason why you cannot use a “U” shape reinforced roof is that it will collapse, which is why the centenary arch or buttressed sprung arch has been used for kilns and building roof, window lintel construction for centuries.
Finally the running temperature in a fireplace will not be anywhere near the bonding (sintering) temperature required to hold the bricks together. The water of crystallization will not be completely removed leaving a structure weaker than when you cast it and able to be crumbled in your hand.
Sorry to dash your hopes, but bricks are the only way to go – common low fired cheap bricks for a pizza over and firebricks for a higher temperature fireplace, Get them second hand to save cost but I strongly advise you not to waste your money and time going down the path you have suggested – learn from the teachings of history.
Posted 14 Feb 11 12:04 AM
Thanks heaps for your detailed post sir!
Maybe one day when i build a kiln to do lime i can think about doing my own fire bricks.
Can you give me a recommendation for a high temp mortar mix to use on these projects.
I think this is the line i am going to go down.http://www.youtube.com/watch?v=TvrUrnEIQoo&feature=related
The double chamber seems like a great idea.
If you have any further tips that would be great.
Posted 14 Feb 11 7:17 AM
Hello again Stonemason,
You do not need to use proprietary mortars for constructing a lime kiln. They are over engineered and too expensive. All you need is ball clay mixed to a slurry paste in water. Remember that what you want to do is seal the gaps between the bricks to avoid heat escape, not ‘glue’ each join in the bricks together.
If you ‘glue’ with mortar, a stress break WILL occur in the wrong place and lift a whole segment of bricks out on alignment and I have seen an arch kiln fail when this happened. No, the principle is to allow each individual brick to move slightly rather than whole segments to move alarmingly - that is why bricks are made to the standard size.
Your suggested ‘double chamber hob oven’ is an excellent design using the downdraft heating method which gives more even heat distribution and cleaner burning operation.
Remember the reason you can see flame burning of the top of any chimney, is because the fuel has not completely burned within the kiln, the super heated unburned carbon monoxide gas is looking for oxygen with which to link and burn, and can find it only in the atmosphere above the chimney exit – hence the flame off the top of the chimney flue.
Not only is this inefficient, but you are polluting your atmosphere with carbon flocks (smoke) and this is a carcinogenic. It is the likely reason I developed oesophageal cancer – no smoke is obviously the best rule.
But let us keep this in perspective – the polluting gasses exiting a typical Potter’s firing kiln, are equivalent to running you car on the motorway for an hour, or running a jet engine for a minute. Take note any of you living under an airport flight path.
Finally, when you read or view American information, remember that they are talking Fahrenheit and not Celsius temperature. You need to divide say 700oF by 1.8 and deduct 32 to convert to 357oC.
Good luck - Rex.
Posted 13 Jan 13 6:02 PM
I just noticed your post a year later! How did you go with brick making. Just wanted to let you know its possible - only you need to make the kiln out of cob and clay and greenery first. A couple of clever inventors have done this alread0, firing pottery, kiln shelves , bricks and lots of pizza and turkey! you might like to check the link. I've included a picture of the bricks they fired. https://www.youtube.com/watch?v=VypiS5X31aA&list=FL5hptEqVH66-y6Xu5yDJUtQ