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rtnaw 06-02-2007 08:40 AM

Firebrick rating?
Hello again,

I am a little nervous about this low, medium, and high duty firebrick rating thing. I just purchased a batch of 125 fire bricks from a local concrete/masonry distributor. They seem to have no idea what low, medium, or high duty firebrick is. I now have no idea what type of firebrick I just purchased. I called most of the contruction and masonry companies in the local area and they don't seem to know either. I am hesitant to start the floor and dome until I know exactly what I purchased.
From what I can gather, the firebrick I purchased is used mostly for fireplace installation. Is there anyway to tell by weight, size or color what the rating of the firebrick is? As always, thanks for any help can give me.


dmun 06-02-2007 08:51 AM

Re: Firebrick rating?
You have the right brick. If the guys at the brickyard don't know what it is, and sell it for fireplace use, it's low duty firebrick. It's typically buff colored, and a bit bigger than a red common brick.

The medium and high duty firebrick come from refractory suppliers, and are for furnaces and kilns. They are considerably more expensive.

james 06-02-2007 08:53 AM

Re: Firebrick rating?
Hi Rob,

Everyone who has bought bricks and jump in as well on this, but here is my two cents.

A majority of the firebricks that the local masonry suppy companies carry are made for fireplaces, and are basically low, or at most medium duty firebricks -- which are perfect for the Pompeii Oven. I didn't even know the differences between the various firebricks when I built my Scott oven -- and I doubt the supply store did either. And the bricks were fine.

High duty firebricks are very high alumina, and are basically made for very high temperature industrial applications (like melting metal) -- and they are something that the average building supply company does not carry. We added the information on high duty firebricks more for people who where finding used bricks (from furnaces, etc.), were being given bricks, or who were finding their bricks from less traditional suppliers -- to let them know what is out there.

Basically, I think you are in tall grass -- and you are ready to go.

What do others think?

james 06-02-2007 08:55 AM

Re: Firebrick rating?
Hey David,

Great minds think the same. Did you see that our two postings were made at almost exactly the same time?

I guess that means we're right. :-)

rtnaw 06-02-2007 10:26 AM

Re: Firebrick rating?

Thanks a lot guys, I can breathe a sigh of relief, I was really worried about the wrong brick and shooting myself in the foot after all the hard work so far. Thanks for the great site and the fast answer.


CanuckJim 06-02-2007 10:31 AM

Re: Firebrick rating?

These things seem to vary a bit, region by region. Here, if you buy firebrick from a masonry supplier, you get 2/3 yellow fireplace brick and 1/3 medium firebrick. The medium brick is a sort of brownish color. These I used for the very center of the hearth. All in all, though, you'll be fine with what you have.


DrakeRemoray 06-02-2007 10:34 AM

Re: Firebrick rating?
Just to put your mind at ease more, I used medium duty, becuase that was all I could find (all the local brick places sold the same brick from the same supplier) and my oven is working really well retaining heat for a very very long time, which was the worry with a high or medium brick. That is, those bricks are supposed to have more insulating properties than the low duty ones. I am sure the ones you have will be fine.


DrakeRemoray 06-02-2007 10:35 AM

Re: Firebrick rating?
And Canuck Jim and I just posted at the same time too...shouldn't we all be out baking?


Balty Knowles 06-23-2007 09:59 AM

Brick Wedges

I saw the photos in the gallery, congrats it looks great. I had a comment about the brick shims photo you posted. I tried to start a new thread re this but couldn't figure it out, I hope some of the other guys catch this & perhaps comment.

I'm not a mason by any means but when I left college 25 years ago I they told me I was an engineer.

Assuming brick has better thermal qualities than the mortar then the I would think the extra brick is good . The wedge shape of the shim however will cause a stress raiser at the sharp end & I noticed back of the wedges were protruding from the dome which makes them vulnerable. In the unlikely event that something strikes the back of the wedge then this could cause a crack in the mortar on the inside of the dome. I would grind the back of the shims at least flush with the outside of the dome to minimize this. Also, whenyou cut the shims leave a flat area on the thin end (say 1/4 ") rather than a sharp point.

Keep up the good work



wlively 06-23-2007 01:47 PM

Re: Firebrick rating?
I am afraid I have to ever so slightly disagree.

I used a similar method of shiming some of the courses. If you are going to cover the dome, you don't need to bother with trimming the shims. Mine were only just sticking out, say less than 1/4 inch and easliy covered smooth when I troweled on the cladding layer.

Agree with preventing stress risers. When using the shims you need to make sure you have mortar oozing out of the joint. The shim is only to prop the brick to the desired angle and hold it until the mortar dries, so there should be a continuous bearing surface under the brick. That way no points of stress.

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