Firebrick - Low duty, High duty

[thecac]

I am beginning to pull the material together for an intended build this summer. I advertised in the local media for firebrick and have a line on a quantity of never-used firebrick very cheap. The problem is that there is no way for me to know whether it is low, mediium or high duty. This is a steel mill town so I suspect that the brick somehow came from the steel mill and that it may be high duty.

Is there any way for me (a firebrick novice!) to determine what duty level this brick is?

Assuming it is high duty, can I use it for my oven anyway? What issues would using it present.

Thanks for the help.

As an aside, one week ago I had never even considered building a wood fired oven and now I cant think about anything else.

Mark

[Frances]

Re: Firebrick - Low duty, High duty

As an aside, one week ago I had never even considered building a wood fired oven and now I cant think about anything else.

Can't help with the brick,sorry, but I can tell you're off to a good start already...

[gjbingham]

Re: Firebrick - Low duty, High duty

Dmun noted something about the comparative weights of low vs high duty brick. Son of a gun if I can remember which is which.

If the brick did indeed come from a steel mill, then I agree with you. Probably high duty brick. The downside of high duty brick is that it takes much more fuel and time to get the bricks to heat to pizza temps. Once they get there, they retain the heat much more efficiently than low duty.

The idea for the Pompeii oven originally stated by James on this site was (paraphrased) that he felt the best brick properties for a pizza oven were those that allowed it to heat up quickly with a minimum amount of fuel, hence the recommendation for low duty bricks. If you intended to use the oven to bake multiple loads of bread after your pizza bake, a medium or high duty brick might be better suited to your purposes. (James - please edit this if I messed up your intent.)

Personally, low or medium duty will work fine. I'd stay away from high duty.

[egalecki]

Re: Firebrick - Low duty, High duty

I believe that high duty bricks are also extremely hard to cut, making it not worth it to use them.

[tigersmith]

Re: Firebrick - Low duty, High duty

Hey Mark,
Low duty firebrick weigh about 8 pounds each. The medium duty weigh less and the heavy duty weigh even less. The way I understand it, the low duty brick absorb heat, the high duty brick reflect heat, (insulate). Those who really know this stuff will chime in shortly, I am sure.
Actually, I wonder if you could use a layer of high duty brick under a layer of low duty brick instead of insulation??? Probably not...Sorry, just thinking out loud.

George

[tigersmith]

Re: Firebrick - Low duty, High duty

Actually,
forget most of what I said in my last post...

See this primer on fire brick: Brick Oven Design | Choose the Right Brick Oven Brick

You will probably have to copy and paste the above link. I haven't figured out how to include links yet.

George

[thecac]

Re: Firebrick - Low duty, High duty

Thanks for the input everyone. I am hearing from all of you that the best way to go is the low duty brick.
My dilemma is this.... low duty brick costs $2.50 ($2 US) a piece where I live in Canada. I can get the new high duty bricks for 50 cents each. I am hearing that they would likely perform ok, possibly taking a little longer to come up to temp but that they are harder to cut. I guess my question is then "how much harder to cut?". Does anyone have experience cutting them?

I will be building my oven on a shoestring and this would be an opportunity to save quite a bit of cost. Having said that, it is only a good deal if I can cut the bricks and if they perform well.

Thanks

[dmun]

Re: Firebrick - Low duty, High duty

I think high duty bricks will work fine. How hard are they to cut? Why don't you buy one of each and cut them in half to find out?

[thecac]

Re: Firebrick - Low duty, High duty

Thanks, great suggestion, why didn't I think of that. I need to go dark for a few days while I am away on a business trip but I will test cut a high duty and a low duty brick when I get back and post my findings.

Thanks again.

Mark

[gjbingham]

Re: Firebrick - Low duty, High duty

One last idea you might consider is sending a PM to CanuckJim. He might know of a source of low duty firebricks in your area of Ontario. He's a great guy and only "yells" at you if you use store bought white bread. Couldn't hurt to try.
G.

[mrsrat]

I picked up a few firebricks today but they had no idea what I was talking about when I asked if they were medium duty. I came home and weighed one and it weighs 6#11oz. Does that mean I bought low duty bricks?

[david s]

I picked up a few firebricks today but they had no idea what I was talking about when I asked if they were medium duty. I came home and weighed one and it weighs 6#11oz. Does that mean I bought low duty bricks?

The high duty bricks are extremely dense and consequently hard to cut. Their density will be over 200kg/m3 (2kg/litre) Medium duty more like around 1.7, As you don't give you brick dimensions you can measure it, work out its volume, weigh the brick and therefore calculate its density. D=M/V. Easiest to work in metric.

[mrsrat]

Sorry they are a standard 9x4.5x2.25

[david s]

Assuming you are talking inches, then your brick volume is 1.5 litres. Weigh it and calculate its density.