Red Firebrick heat tolerance

[pianomark]

I recently got a great deal on about 150 red firebrick (as well as some regular cream colored firebrick, and a whole lot of regular clay building bricks).  These are all clean unused bricks, been stored up to about 15 years.  My understanding is that red firebrick is somewhat less tolerant of high temperatures.

Is that true?   Is there any way to test these for high heat resistance?

I am thinking maybe I can use them in the interior bell walls, as long as I keep them lower than the top of the riser.

Any thoughts?

Thanks

[Deleted]

The maximum recommended service temperature
for red bricks is about 1750 degrees F (945 C).

However with an alumina content above 25% the service temperature may be much higher.

Use a high power gas torch.
Propane flame temperature around 2192°F/1200°C
Butane flame temperature around 3092°F/1700°C

Heat a spot on the brick untill it glows yellow orange.
If a brick can endure that for 10 to 15 minutes whithout cracking
it has a good fire and thermal shock resistance and can be used everywhere in a stove.

[pianomark]

Thanks, Karl,

Exactly what I wanted to know.  I wasn't sure if such a test would immediately indicate heat intolerance, or if the failure might only happen over time with repeated thermal cycling (too late if it's already in the stove!)

[josephcrawley]

Red bricks are fine as long as they are not in the firebox or riser. I've used them for the main bell of several stoves with no problems.

[pianomark]

Just to clarify my original post, the bricks I am wondering about are definitely firebrick ( 9 x 4.5 x 2.25 with sharp square corners ), the retired mason I bought them from said they are firebrick. He said they were just colored red to give them an "antique" look (maybe he was having me on, trying to get a better price). I suspect they are a lower quality firebrick, perhaps made with lower quality (less alumina?) red clay.

So I am talking about red firebricks, not common red bricks. I have yet to perform any heat testing.

[Deleted]

Relatively mall amounts of red clay in fire bricks can save a lot of manufacturing costs
by lowering the sinter temperature by several hundred degree Celsius without
inflicting much negative impact on service temperature.

[Orange]

maybe they are magnetite bricks: donkey32.proboards.com/thread/2329/magnetite-heat-storage-bricks?page=2

[patamos]

I was asking a similar question a while back. Thanks Karl for the help on that one. I also put question out to builders here and there and the general sense i get is that the softer fired red bricks are better at handling intense thermal cycling due to their higher porosity - but much depends on their chemical make up. And of course the softer the brick the less it is able to handle mechanical stresses like loading big chunks of wood in the fire box. So there is a trade off.

Lars Helbro, who builds single skin clay brick heaters in Denmark summed up by saying: So long as they do not regularly experience temps above 570c, any clay brick will work.
It is then a matter of knowing where in your heater that transition point is. ONe general rule I hear is 'a few feet down stream from the fire box'. Or, to be cautious, 2ft per Kw of heat during max use.
This is easey to figure out in heaters with long flue runs, but more challenging in tall narrow heaters where the firebox is in close proximity.

[pianomark]

OK,  I did the test with a propane torch as described by Karl above, and the brick came through just fine, it now has a dark spot where it had been glowing orange.  No cracks or deterioration in hardness or abrasion resistance.  So I think they will be fine in any part of my bell, although I'll still try to keep them below riser height as a precaution.

So maybe the mason was correct, they are just firebrick that are colored red for asthetics.  They are not as dark a red as the smaller, much lighter weight common building bricks, so as Karl said maybe they just added enough red clay to color them and save cost without compromising refractability.

Thanks, everyone, for your responses.