Brick type decission to be made

[nissanneill]

Hi all,
I have been researching the building of a wood fired oven and when I came across this exceptional site, I have become confused with what one can only decribe as "information overload" as to which direction to go.
As it has been suggested by other members within this forums, (I have read and printed out hundreds of pages) fire bricks are the preferred matyerial from which to construct your oven but they are relatively difficult to acquire and quite expensive here in Australia. The going price is between A$4 and $5.50 each.
I have bought Russell Jeavons’ book (from the UK through Amazon) only to find that his restaurant and ovens are only 25km away from me, where he uses old “pressed reds” bricks for all of his ovens. He has built 4 in total which are used commercially, two in his restaurant. The picture of the bricks in his book show bricks that were typically made here some 50 to 100 years ago in Adelaide. To satisfy my curiosity, I am going to his restaurant in 2 weeks for a meal to check out personally his build materials and technique. I am also enrolling in 2 of his many courses that he is offering with regards to wood fired ovens and using/cooking in them.
I have also been doing some experimentation with a 1200?C fired solid clay paver 230 x 115 x 70mm @ .85c each and a fire brick 230 x115 x75mm (which is 6 times as expensive) @ $5 each.
I aquired the two sample bricks from a ‘local’ brick kiln that supplies many oven builders with both types of bricks. They maintain that they supply more builders of ovens with clay pavers than their firebricks.
I drilled a 55mm deep x 5mm hole into the 'mathematical centre' of the brick, put in the thermocouple probe and siliconed it in so that it was sealed from the surrounding heat and only gave the temperature increase that permiated the brick through to the centre. I then put the bricks into our new kitchen fan forced electric oven set to 180?C and read the temperature increase as the brick heated from all 6 sides. I used a Digitech QM1600 digital thermometer with 2 thermocouples. The results are as follows:
Brick #1:Red clay paver and brick #2: Cream Fire brick
Time elapsed
Brick #1 #2
5min 17?C 17?C
10 min 27? 21
15 min 40? 28?
20 min 56? 41?
25min 71? 54?
30min 86? 67?
35min 97? 79?
40min 103? 89?
45min 104? 97?
50min 104? 108?
55min 104? 114?
60min 104? 121?
I then removed the bricks from the oven, sat them on newspaper on the kitchen bench and recorded the following figures whilst they cooled.
10min 81?C 106?C
20min 75? 97?
30min 66? 85?
40min 59? 76?
50min 51? 65?
60min 49? 61?
70min 45? 56?
80min 42? 53?
90min 40? 48?
100min 37? 45?
110min 35? 41?
120min 32? 38?
These results seem contrary to what is generally believed. The red clay paver absorbed the heat quicker and gave up the heat quicker than the fire brick but ceased to heat up more than 104?C whilst the fire brick continued to increase in temperature. (This may be due to the thermocouple measuring the air in the hole rather than the internal brick surface. I should try the test again and switch the thermocouples). I am not surprised by the findings as darker objects absorb energy more readily than lighter objects, as with the paler cream fire brick.
The brick manufacturer maintains that the pavers will be quite stable and not deteriorate until the bricks reach their firing temperature of 1200? C which is highly unlikely.
With this information, which brick would be preferred for both the hearth and the dome of my oven?
Has anyone got any ideas or more importantly any similar experiences using such materials?

Neill

[james]

Hey Neill,

There are some really good questions here -- some of which is made more complicated by the fact that your local firebricks are $5, not $1.25.

I can add a couple of things here, and see what other folks have to offer. I have talked to various people with different expertise about the difference between clay brick and firebrick on the basic questions of longevity, heat up time, high heat retention, and moderation heat retention.

In terms of clay bricks breaking down, there is no issue with high heat (they are fired at very high temperatures). The issue is thermal cycling, where they will be heating up to 1000ºF, then down to zero, each time you use the oven. Clay bricks are prome to spalling with thermal cycling, where small pieces begin to flake off over time. It's the expansion and contract where they have trouble. In my personal experience, I had a chunk of brick crack and fall down the first year of operation with a red clay brick dome. Still, this isn't a huge issue. If you think about how often you will use your oven, and how long you want it to last, it should be OK.

In terms of absoring and holding high heat, my experience is that firebrick are better. I have two ovens of similar design, one with clay brick and one with firebrick in the dome, and I find the firebrick oven is more responsive at higher temperatures (600-800ºF). Your test was lower temperatures, and I'm not sure what to take from that. Firebricks have set percentages of alumina and sillica, which are set to efficiently conduct heat at those higher temperature.

To relate this back to precast ovens, there are less expensive ovens made from clay and better ovens made from controlled refractories (like the ones FB sells). My experience cooking in low-end clay ovens and the FB ovens also confirms that the better materials are better at coming up to heat and holding heat. You can feel the difference.

For a Pompeii builder, I think that if a red clay brick is $.40 and a firebrick is $1.25, you should build with a firebrick (if you have the budget), and also that it is also OK to build the dome with red clay brick -- either if budget is an issue, or is your local firebricks are $5.

I would be interested in hearing what other folks think.
James

[nissanneill]

Thanks for the reply James,
I am well aware tof the potentioal breakdown of the bricks over time but many people are using clay bricks for obvious financial reasons.
I just visited a huge demolition site yesterday and bought a couple of sample firebricks at $1.00 each from a huge boiler in an old abatoirs which will make the oven far more viable. They are a little knocked around as they are possibly 50+ years old but I can pick through the10 pallettes for the best.
I have done a search of the company which was bought out in the Dandenong district of Melbourne in the 50's and I am not sure of the rating of the bricks. They weigh just bunder 3Kg, for the standard brick size of 230 x 115 x 75mm, the same as the $5 local bricks. I will contact the kiln tomorrow to check on their content.
I have no worries paying the price for the bricks but the oven is only a very small expense when compared to the other renovations that need to preceed it and after the build. I also have 2 kit cars from the UK to finish building and another wedding (the last daughter) in 6 months to finance, so I need to watch the dollars.
Whilst I have your attention, I am playing with designs for casting some cast iron oven doors (at this stage looking at double doors 500mm wide, 300mm high at the edges and 380 max in the centre of the arch), and frames for the oven. Only prototype sketches at this stage but looking for ideas and innovations. Any suggestions?
When I work out how to post pictures and scans will put them up for comment before I make the patterns.
Have just purchase a 14" diamond saw blade for cutting the bricks (need to make the saw now with graduated scale forcompound angle cuts) so the oven and doors are definitely on the way.

Regards

Neill

[jengineer]

3 Kg per brick (6.6 lbs)
230 x 115 x 75mm (9 X 4.5 X 3 inches)

Sound like they will work - good find

[edschmidt]

Great discussion,
Ill take issue with one thing though, James states that a clay oven is a lesser oven. I dont have personal experience with a clay oven but cannot understand how a well made vetrified clay of proper materials (IE fireclay, grog,etc) would be inferior to a cold cast refractory. I actually built my oven from a castable refractory and have had no problems, but arent firebricks just properly formulated and fired clay?
Just wondering.

[nissanneill]

Thanks guys,
decission made! Will get off the net, call the brick manufacturer for their fire brick content and then go out and spend half a day sorting the best secondhand bricks for use. Lucky I am on holidays at the present.
Drew up my plans for a 1000mm internal dimensiom Pompeii oven with 2 swing cast iron doors last night and looking promising. A total of 143 full brick only needed for the hearth, first row of standing soldiers and the remaining cut half brichs, 10 rows in total. Casting the frame will cause major problems with tapers and relieving when the patterns are pulled from the sand mold so guess it will be made from heavy grade angle and rolled flat lintel bar.
Will post some pics when I get it underway shortly.

[james]

Way to go Neill,
It'll be fun to get going, and enjoy your holiday.

Ed, I will take a stab at answering your question, and look forward to hearing with other folks have to offer. I think we are pushing the collective ball forward on this topic.

When you ask "what's the difference between vetrified clay of proper materials (IE fireclay, grog,etc) and a firebrick", I think you put your finger on it. Isn't a firebrick a brick with the right material? It's the material that matters, and red clay bricks don't have a complete mix. For example, our terracotta bakeware producer buys clay from Montelupo (an area known for good natural clay), then adds 45% alumina they import from Germany to make the final mix before the pans are fired. That allows the pans to conduct heat better and it makes them more temperature and thermal cycle resistent. It costs more, but it makes a better pan.

I think this translates to bricks and ovens. My experience with a clay oven is interesting. It was made by a mid-tier oven producer in Tuscany. What is interesting is that they sell two lines of ovens using the same forms. They sell the clay ovens through building supply stores, but you can special order refractory ovens the same sizes as the clay one. The refractory ovens use the mix (binders and a fired/ground firebrick aggregate) they use for their commercial ovens -- and they cost a lot more. One of our competitors in the States does the same thing. A line of entry level clay ovens and a line of more expensive refractory ovens.

I installed the clay oven and used it for a year, and it wasn't great. When I installed the second oven (a Casa), I felt you could really tell the difference.

So I have anecdotes and things producers tell me.

What do other folks think?
Jame

[nissanneill]

James,
You convinced me with the fire bricks and well, I are now under way. I have purchased and collected 200 fire bricks around the back this very evening. I sorted through 3 palettes for good ones. The very accurate scaled plans that I did last night requires 143 full bricks for the hearth, first row of standing soldiers and the remaining 9 rows/chains utilising half bricks.
I cheched with the refactory manufacturer in Bacckus Marsh, Victoria, and they claim that their medium use bricks, Darley 26 weigh around, 4kg (in fact their specs calculate to 3.689 Kg), their Darley 38 - 4.5Kg, and their Darley 48 around 5Kg each. In the ones that I collected today, I found around 10 bricks that weigh closer to 6 Kg. I was thinking of putting then to one side of the general oven hearth for special cooking as I believe they are the high temp bricks that could be used to cook pizza when the remaining oven temp drops to bread baking temperatures. They will be easy to remove or replaced if/ whenever needed.
Still working on the cast doors with fellow member Hendo and will keep you in formed of progress.

[dmun]

The alumina in the refractory products is a by-product of the aluminum manufacturing industry. It isn't a traditional material. Like our high-tech insulation products, it's better than the traditional stuff.

[james]

You learn something new every day.
James