firebrick conundrum. Help needed, not offered.

[dmun]

Heavy duty brick are heavier in weight? I thought it was the opposite. Most of what I think I've read seems to suggest that light duty=heavy weight; heavy duty=light weight.

Links? This may require more than my "what I've heard" approach. Please share your research with us.

[KEmerson]

Any notion I got about this was right here. I can't find any, though; I've been all over this forum for many months and cannot pick through the haystack for that particular needle. And it is very likely I simply misunderstood, but I will say that I feel I read it more than once. Maybe some posts were not clear themselves. Who knows? But I thought that to a great extent we are paying attention to the alumna/silica ratio. That more alumina makes a brick heavier duty all the way to becoming insulating brick. That alumina weighs less than silica so that the balance would mean more alumina = lighter weight than the reverse. So I thought a higher % of alumina i.e. above 30% or so just makes a brick heavier in its duty rating - or whatever that's called.
I may have been confused by James' brick primer. He mentions that insulating brick is very light weight - 2#. And that heavy duty firebrick has a very high alumina content. So in my head alumina then is lighter than silica and my logic told me (nasty logic!) that more alumina means heavier duty means in turn lighter brick. I may have seen heavy duty and insulating brick as either the same thing or close to it.
So, if you please, rather than my proving my apparently misguided research, could I just have the straight poop on this. I tend to doubt I'm the only one so confused. But I could be.
Thanks very much for the help. This forum is a far better resource, it seems, than even the vendors are.
Kim

[RTflorida]

Kim,
I don't think you are any more confused, just fretting over it more than most.
In my speaking with a refractory specialist (remember this was over 2 1/2 yrs ago, so my memory may be spotty) I was told the terms "light", "medium" and "heavy" are not used in the refractory industry.....these are generalized terms used to categorize bricks for non specific applications. Industrial applications require specific duty ratings and would never utilize bricks sold by such generalized terminology.
As I was told, a "light duty" could have a alumina content from around 18% to around 35%, "medium duty" from 35%-48/50%, and "heavy duty" up to 80% (usually in the mid 50s-60s).
Naturally, these varying formulas are going to affect weight, not to mention the exact dimensions.
We do not have an actual firebrick manufacurers representative who is highly active on this forum (at least no one stands out to me), so we use a lot of the generalizations. Remember, space shuttle technology is not needed to build a perfectly functional oven that will last a lifetime.

Generally speaking (using that term again), ANY one of the 3 brick options you have listed above should work fine; #1 and #2 most definitely, #3 does sound a bit light but they certainly do not sound like insulating brick (yes, they are only 2-2.5 lbs and are almost always white in color) or "heavy duty" (yes, they are the heaviest at over 9 lbs). I have held them all in my hands and at the time of my build, I read the MDS for all of them.

If you REALLY must know, you are going to have to find the specific manufacturer for each of your options and request an MDS for each. As I mentioned, I went to a refractory specialist and learned everything I though I needed to know, then found and purchased bricks that were simply sold as light duty fireplace bricks at a normal brickyard (no MDS provided) because they were far cheaper than the other suppliers.

Just pick one of the 3 and get building, you will be fine.

RT

[Gromit]

Kim,

You could also purchase this
Pompeii90 Oven Kit :: Installation Accessories :: Forno Bravo Store or this Pompeii110 Oven Kit :: Installation Accessories :: Forno Bravo Store and have 100% peace of mind that you are buying the right materials.

[KEmerson]

RT: Thanks, that's about all I needed.
David: Thanks but I just needed clarification on something confusing me. I'd rather do all this leg work, gather what I can and build. I enjoy this learning process almost as much as I enjoy the building and the results. Kits are what I avoid.

I'm generally happy with the bricks I've found. The #1 brick is probably safest all around. Thanks all.
Kim