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waynespizzaworld 01-25-2011 01:59 PM

light duty verses medium duty
I am currently planning a second oven for a friend that will be slightly different in design and size than the first oven. If anyone is interested in seeing photos of the first build the link here Picasa Web Albums - wayne - Wayne's Pizza... will get you to a photo album showing this build. Big thanks to this site as I could not have built this first oven without its support.
My question is regarding the fire brick. I used a light duty last time and I am very happy with it but have never used another oven or even seen another oven in operation so I don’t know what to compare mine to. I understand the plans now recommend a medium duty at 38% alumina. My local source for brick can ONLY get me the same light duty that I used last time rated at 24-29 percent alumina.

1-How much difference will there be in going with the medium duty?

2- I am assuming it will take longer to heat up and hold its heat longer but also will get hotter. Even with pizza’s now I feel like my floor can get a bit hot and I need to let it cool for a good 5 minutes after brushing off the coals from floor. I can heat my oven easily in 45 minutes for pizza temps. All bricks burnt to clear and roof at around 800 degrees or hotter. If I go with a medium duty how much do you think the above characteristics will change?
Thanks for this Wayne

david s 01-25-2011 02:52 PM

Re: light duty verses medium duty
I think that the general consensus is that the extra cost of heavy duty bricks is unwarranted for the, marginal improvement in performance. These bricks are designed to perform to temps about four times that to which we fire. You probably wouldn't notice the difference anyway.

waynespizzaworld 02-13-2011 06:57 PM

Re: light duty verses medium duty
It is medium duty not high duty I am asking about here. It just seems odd that when I built my last oven light duty was what I think folks were recomending. Now FB kits come with medium duty and FB is recomending using medium duty. I may waste 500 extra dollars on these bricks compared to light duty in Canada.
I guess may main question is how much longer to heat a 42" oven with med instead of light duty and also how much longer will the mediums hold heat than the light duty.
I don't want this to sound like a complicated science project but I do need to know the answer to both these questions and hoping that I can be saved from the grief of paying too much for a med duty that is not really going to add to the oven or it may even be worse if it takes too long to heat up.......CONFUSED IN CANADA.....wayne

DrakeRemoray 02-13-2011 09:44 PM

Re: light duty verses medium duty
I think light duty is still preferred. I think either would be fine, but med duty is supposed to shed heat faster too, which can lead (supposedly) to burned crusts on the bottoms of bread from the hearth shedding heat faster. I would save the $500...

david s 02-14-2011 01:02 AM

Re: light duty verses medium duty
I think it complies to the law of diminishing returns. You can pay a lot more, but get a hardly measurable difference. A bit like the Hi Fi buffs in the 70's. I'd go for the light duty, but if you've got the spare cash...

dmun 02-14-2011 07:18 AM

Re: light duty verses medium duty
The big problem with medium duty firebricks is that they push you over the threshold from brick yard, which is a high volume, high competition business, to refractory suppliers. There's much less competition and therefore much less price flexibility once you switch to the lower volume suppliers. I think this accounts for the price difference rather than a real alumina/silica price differential.

I don't think there's any real difference in performance at the temperature levels we run at.

waynespizzaworld 02-14-2011 08:10 AM

Re: light duty verses medium duty
Thanks guys, good advice. You have just saved my 500 bucks. Appreciate it..........wayne

RTflorida 02-14-2011 08:15 AM

Re: light duty verses medium duty
dmun, well said. Remembering back, light duty firebricks ranged from $.77 to about $1.60 each at the brick/stone yards. The medium duty and heavy duty started at over $2.50 each and went over $6.00 at the 2 refractory suppliers I visited. There were considerably more choices at the refractory suppliers - several different colors, several different angles of arch bricks, as well as different sizes of bricks and hearth type blocks. All of this came with a steep price as well as a minimum 7-10 day wait.
I opted for the cheapest instock option ($.77) light duty bricks from the same brickyard that had the lowest price in the state for heatstop ($55 a bag). I can't compare them with anything else, but I have been very happy with my oven and performance. So far no cracking or spalling and no signs of wear on the hearth. I'm pretty certain I could not be happier if I had spent 2-3 times more for the medium duty.


lwood 02-14-2011 07:56 PM

Re: light duty verses medium duty
So what did we determine? What is the real difference between light medium and heavy duty fire brick, as it applies to us. I have heard heat retention and wear as the primary considerations. Heat retention is what I am really interested in. Do the higher duty bricks actually hold more heat?

david s 02-14-2011 09:22 PM

Re: light duty verses medium duty
Yes, because they are denser.

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