# What causes firebrick to crack ?



## 740jsmayle (Jan 23, 2015)

I had a fire brick crack during the 13/14 heating season. I replaced all my fire brick. I noticed this a.m. while filling my furnace that there is another one cracked. Just curious as to what causes this ? operator error or bad bricks?
Scott


----------



## aarolar (Jan 23, 2015)

The ones in my Fisher are probably 30 years old and still in one piece so I'm thinking its brick quality.


----------



## Chris-PA (Jan 23, 2015)

It may also be how tight they fit, or some stress point.


----------



## Marshy (Jan 23, 2015)

How hard do you throw you wood into the firebox could make them crack. Otherwise its not impossible to crack them if you heat them fast enough but not as likely because it would have to be heated really damn fast.


----------



## Del_ (Jan 23, 2015)

Just a theory:

For the first fires of the season firebrick may have a high moisture content absorbed over the summer. I've read that even cast iron stoves can absorb moisture over the summer and that the first few fires of the season should be light to drive out this moisture before heavy firing. The other reasons listed above are sure to be factors.


----------



## Fred Wright (Jan 23, 2015)

Oversized splits, overfilling the firebox, impact from tossing logs in the furnace, inferior brick. Any of these scenarios can result in broken bricks.

We replaced several broken bricks last year and the year before. This year we've had no broken brick. Only thing we're doing different is burning smaller splits than before.


----------



## Whitespider (Jan 23, 2015)

Heat stress would be the most likely _raison d'être_... not that other factors such as impact won't contribute, but heat stress first.
I have yet to crack a side brick in my furnace (second season), and I just _toss_ large chunks of wood in there (plenty of impact)... but it has a large unlined firebox area above the brick and forced air flowing across the outer skin to pull heat away. My secondary combustion stove on the other hand does not have the large unlined area or the air flow, and I don't _toss_ wood in it (I'm actually careful about impacts). During secondary the heat is extremely intense (admittedly, I run it hard out in the shop) and it cracked bricks all the time. I finally quit replacing the side brick... there's just the brick on the floor now (most cracked). It actually throws more heat without the side brick... but I'm guessin' it wouldn't pass EPA testing without them.
*


----------



## GVS (Jan 23, 2015)

740jsmayle said:


> I had a fire brick crack during the 13/14 heating season. I replaced all my fire brick. I noticed this a.m. while filling my furnace that there is another one cracked. Just curious as to what causes this ? operator error or bad bricks?
> Scott


All good answers to this question.


----------



## GVS (Jan 23, 2015)

740jsmayle said:


> I had a fire brick crack during the 13/14 heating season. I replaced all my fire brick. I noticed this a.m. while filling my furnace that there is another one cracked. Just curious as to what causes this ? operator error or bad bricks?
> Scott


All good answers to this question.


----------



## Marshy (Jan 23, 2015)

I wont replace a cracked brick unless its at risk of falling apart or has fallen apart. Just a crack alone wont hurt anything IMO, its still serving its purpose. I have one brick that is cracked 3 ways from a hard impact and I'll just leave it until a piece comes off and falls into the firebox. Replacing them every 5 years seems like a waste of money and time IMO.


----------



## Henry Fuller (Jan 23, 2015)

Marshy,
I agree with you what you saying about fire bricks replacement not needed, I have been serviced customer multi-wood combo. furnaces with minor brick crack 2 or 3 ways (as long they stay locked together and not loosen up). I see that you are about 15 min. ride up north from where I live. We have been very lucky with the weather we are having below you (so far).

Henry


----------



## haveawoody (Jan 23, 2015)

I used to get cracked bricks from cleaning to much ash out of the woodstove.
Clean bricks with hot fires are a bad combination, leaving 1" of ash in the woodstove and no cracked bricks since for me.


----------



## Marshy (Jan 23, 2015)

Henry Fuller said:


> Marshy,
> I agree with you what you saying about fire bricks replacement not needed, I have been serviced customer multi-wood combo. furnaces with minor brick crack 2 or 3 ways (as long they stay locked together and not loosen up). I see that you are about 15 min. ride up north from where I live. We have been very lucky with the weather we are having below you (so far).
> 
> Henry


 
Hi Henry,
Its been a weird winter for sure, more mild than last year and not nearly as much snow. We could use another foot of snow on the trails to smooth the ride though. All this cold weather at night the last 2 weeks and no lake effect is strange, but Im not complaining too much because if the wind was blowing it would have probably doubled my firewood use. 15 minutes south should put you between Central Square and Fulton, we're practically neighbors!


----------



## 740jsmayle (Jan 24, 2015)

My furnace is like Whitespider it only has one row on the sides . I have been really careful not to throw splits in. I was thinking that could have caused it. As some have said it is not a problem so I guess I won't worry to much about it. Thanks for the replies much appreciated !!!
Scott


----------



## Vangellis (Jan 24, 2015)

I've had some in my stove that have a crack but have not fallen apart. The stove is coming up on 30 years and I haven't replaced a brick. All is well so far.



Marshy said:


> I wont replace a cracked brick unless its at risk of falling apart or has fallen apart. Just a crack alone wont hurt anything IMO, its still serving its purpose. I have one brick that is cracked 3 ways from a hard impact and I'll just leave it until a piece comes off and falls into the firebox. Replacing them every 5 years seems like a waste of money and time IMO.


----------



## Del_ (Jan 25, 2015)

https://www.google.com/search?q=moisture+cracking+firebrick&ie=utf-8&oe=utf-8


----------



## Whitespider (Jan 30, 2015)

Wouldn't ya' just know it??
It's been a week to the day since I posted on this thread I ain't cracked a brick in my furnace even though I just toss large chunks of firewood in.
Well this morning I'm tossin' and I hear a funny clank-like noise... look inside... well I'll be damned... cracked a brick on the right side.
I go back to to tossin' a couple more chunks and the same funny clank... look inside... well I'll be damned... cracked a brick on the left side.
Me and my big friggin' mouth‼
*


----------



## Erik B (Jan 30, 2015)

Whitespider said:


> Wouldn't ya' just know it??
> It's been a week to the day since I posted on this thread I ain't cracked a brick in my furnace even though I just toss large chunks of firewood in.
> Well this morning I'm tossin' and I hear a funny clank-like noise... look inside... well I'll be damned... cracked a brick on the right side.
> I go back to to tossin' a couple more chunks and the same funny clank... look inside... well I'll be damned... cracked a brick on the left side.
> ...


Should have knocked on wood when you said something about not cracking any firebrick


----------



## Fubar (Jan 31, 2015)

i have found some stoves that expand an contract rapidly will break the bricks if they don't have some clearance , and they also just cook over time and just start cracking naturally , i use to run a forge, it burned bricks up regularly, where the most heat was they would just crumble to dust ,also i don't think the new fire bricks are as good or withstand as much heat as the old "usa " made ones .


----------



## BeatCJ (Jan 31, 2015)

I'm thinking about soapstone in mine. I don't have that many to replace. Price is about 2 - 3 times what cheap Rutland bricks are, but I bet they will last more than 3 times as long. Trying to decide if the thermal properties in my stove would be worthwhile.


----------



## laynes69 (Jan 31, 2015)

BeatCJ said:


> I'm thinking about soapstone in mine. I don't have that many to replace. Price is about 2 - 3 times what cheap Rutland bricks are, but I bet they will last more than 3 times as long. Trying to decide if the thermal properties in my stove would be worthwhile.



I've heard of soapstone's cracking when a stove gets too hot. Placing them inside a firebox may be an expensive mistake. Standard firebrick are pretty dense and will take the heat.


----------



## 740jsmayle (Jan 31, 2015)

Are all firebrick the same quality regardless of what name they are sold under ?


----------



## BeatCJ (Feb 1, 2015)

laynes69 said:


> I've heard of soapstone's cracking when a stove gets too hot. Placing them inside a firebox may be an expensive mistake. Standard firebrick are pretty dense and will take the heat.


I'm not impressed with the standard brick I was able to buy for my stove. I do understand that they are exposed to extreme conditions. I would suspect that soapstone will stand up to the same conditions, though. I know it is used to line fireplaces and stoves. I would bet it, like commonly available fire brick is most likely to crack during rapid changes in temperature.



740jsmayle said:


> Are all firebrick the same quality regardless of what name they are sold under ?


I doubt it, but I couldn't tell you which (if any) brand is better than another. I would doubt the least expensive, most common brands (Rutland and Vogelzang) are the better bricks, but they are what is available.


----------

