Composition of clay flue tiles?

[Marty]

I was asked what the melting point of clay flue tiles is and cannot find the answer.

I assume it is 2800-3500 F or so like fire brick but do not know.

Is anyone familiar with any standard industry practice for the manufacture of clay flue tile liners if there is one?

 

[Marty]

This appears to be a little known subject...

How about this question:

"How hot can a chimney fire get?"

 

[Roospike]

Right before the point of clay flue tiles melting. :cheese:

 

[Marty]

Right before the point of clay flue tiles melting. :cheese:

Yeah, thats what I was telling him, but this guy wants to hear it in terms of science.

I'm guessing that whoever makes them uses the closest clay they can get their hands on and adds 'who knows what' to the mix, with no particular attention paid to the normal fire clay manufacturing process for industrial apps.

Oh well.

Unless BeGreen wants to make a clay flue tile burning video I guess it ends there.

 

[Roospike]

Dont know what there rated for ( 2100° I would think or more )

 

[restorer]

Two sources said they are rated at 1,800* to 2,400* F. The "melting" point will be many times that temp. Realize, they line ovens that melt steel and iron with brick. The electric furnaces for refining many other minerals are lined with brick and never melt. Koalin clay has a lot of things added to enhance it's resistance to heat. Special high temperature ceramic liners can handle thousands of degrees higher, think of the tiles on the space shuttle.

 

[BrotherBart]

OK. I found one manufacturer of the stuff that says that they are tested to withstand 1,000 C for 30 minutes. That would be 1,832 degrees Fahrenheit. Continuous temps of 600 C which is 1,112 F.

Pretty much the same as UL1777 for stainless liners.

 

[elkimmeg]

What is the temp of a mapp torch? as it did nothing to the clay flue exposed for 5 minutes all it did was change color

Fire clay flue linings (ASTM C-315) with a 5/8" wall thickness governs the manufacturing process. They are used in low heat appliances as found in residential applications

Low heat is the range below 1200 degrees they are tested to 2000 degrees for 5 minutes to reflect the normal range of a chimney fire

Chimney fires occure in a heat range of 1800 degrees or less. A chimney fire is not hot enough to melt the fire clay, but sudden high heat exposure can crack and destroy them


As to what temp it melts, I suspect it is the same temp of molten rocks. Most chimnys are not exposed to lave flows and Volcanos over 2000 degreess

 

[Marty]

...

As to what temp it melts, I suspect it is the same temp of molten rocks...

Right. Which varys widely.
I guess they test to UL standards but some degree of luck, if you would call it that, would be involved in the composition of the final product. If the base clay material is derived from a fortuitous blend of minerals your melting temp would increase. Not that one would worry about them melting in a real world setting... it's more of an academic question than any real concern about the safety of a clay linner.

Thanks to everyone for the feedback.

BB, I'll tell him about UL 1777 and tell him to do a chemical analisys of a sample from his chimney if he wants to know the exact melting point.

 

[GVA]

Here's another question..... What about the mortar between each of these clay tiles? What is this rated for?

 

[BrotherBart]

Here's another question..... What about the mortar between each of these clay tiles? What is this rated for?

In most cases it isn't rated for anything. It is pretty much accepted that even though codes call for refractory mortor that virtually all chimneys flue tiles are installed with the same plain old mortor that the bricks are buttered with.

 

[Marty]

Here's another question..... What about the mortar between each of these clay tiles? What is this rated for?

I found this rough guestimate: "the melting point of concrete varies between 1800-2500°C. "
(broken link removed to http://www.meg.co.uk/meg/app10.htm)

 

[GVA]

well I don't know about the melting point but if you get a torch close to concrete it tends to pop and blow a chunk right out of the floor.
So I guess I was wondering what a chimney fire could do to degrade and,or loosen this mortar.

 

[Marty]

The temp difference between the inside of a clay flue tile and the outside during a sudden chimney fire is what causes them to crack as well ...so I would suppose the same would apply to the morter. I think that's the best safty related argument behind a steel linner inside of the clay tiles you end up with a double fail safe... not to mention 'if you steel liner is damaged it's a lot easier to replace than the clay tiles.

 

[DriftWood]

As to what temp it melts, I suspect it is the same temp of molten rocks. Most chimnys are not exposed to lave flows and Volcanos over 2000 degreess

"I have never actually remelted magma, but it is done in the lab. I do know that magma melt ranges from 1000 to 3000 degrees celsius, so it would take a high temperature furnace to reach the lower limit. The higher the silica content the easier the melt I would assume."

http://answers.google.com/answers/threadview?id=46463

 

[Eric Johnson]

Here's another question..... What about the mortar between each of these clay tiles? What is this rated for?

In most cases it isn't rated for anything. It is pretty much accepted that even though codes call for refractory mortor that virtually all chimneys flue tiles are installed with the same plain old mortor that the bricks are buttered with.

You're supposed to use refractory cement. I'm sure people do use regular mortar, as BB says, but I'd think it would crumble and fall out after awhile. I've cleaned enough nasty old clay liners in my day. Gimme stainless any day of the week. A sweep I used to know said it wasn't uncommon to find chunks of clay liner mixed in with all the creosote in the cleanouts of chimneys he would clean. He said all he could do was tell the owner (or tenant) that it was time to get a new chimney, but they rarely did.

Up in the Adirondacks if you have a bad chimney fire in an external, clay-lined chimney, the volunteer fire departments don't think twice about pulling the whole works down if they think there's a chance of the building becoming involved. Then you've got a stinking, smoldering pile of rubble in your yard and no heat.

 

[elkimmeg]

Well I got called away to view another chimney fire. More paper work in the morning. IT was an old I guessing here garison slam in installation. No visable tags on the stove to identify it
This was a real burner, Cresote factory, finally touched off. A lot of smoke damage in the home. I don't know if the FD will allow the residents back in tonight. When I left, they had the big fans aring it out. They dropped one of those bag dry chemicles bombs to put it out. I had FD remove the stove from the home,so that it would not be used again. The clay liners did what they were suposed to do., contain the fire, but the fire cracked them beyond repair. I never see the full blown fire. I'm called in afterwards to follow up. No fire damage beyond the chimney only smoke damage to the home, also no water damage Those dry chemmicles prevent extensive water damage. Guess what there were split near the stove and they were not close to being seasoned..

Part of the decision to allow thm back in the home. is to figure out if the fire damaged the flue connected to the oil burner. Due to its so cold I think the FD will not shut down the boiler to prevent freeze up damage. My guess is, they will not be returning tonight , but in day light when the second flue condition is determined a decision will be made.

 

[Eric Johnson]

Sadly ironic that this stuff always happens when people can least afford to be left out in the cold.

 

[Martin Strand III]

Right before the point of clay flue tiles melting. :cheese:

Yeah, thats what I was telling him, but this guy wants to hear it in terms of science.

I'm guessing that whoever makes them uses the closest clay they can get their hands on and adds 'who knows what' to the mix, with no particular attention paid to the normal fire clay manufacturing process for industrial apps.

Oh well.

Unless BeGreen wants to make a clay flue tile burning video I guess it ends there.

Marty:

I have no info on the maximum temperatures clay flue liners can take before melting, sorry. But it's very high.

However, I do know that they (the red clay flue liners) are made from clay and are then fired (like bricks) in a kiln at high temperatures unlike concrete, which is a mix of portland cement and an aggregate hardened by chemical reaction. Flue liners are not concrete as one poster in this thread may believe.

Red clay, in flue tiles and bricks, is red due to an impurity, iron, in the clay. Impurities like iron (and lime) lower the melting point of the final fired masonry unit while another ingredient in clay, tends to raise its melting point: alumina. A high alumina clay has a higher melting point, like porcelain. Clay also contains silica which undergoes change in its crystalline structure and contributes to a fired clay's brittleness. All these materials work together "in the mix" to give the final flue tile or brick its properties. Oh, whiter "fire brick" has less iron, less impurity, therefore has a higher melting point than an ordinary brick explaining why it's commonly used as a firebox liner and why your stove costs a little more than if the firebox were lined by red brick (less $) which may be OK since it can take the heat there but may crack a bit easier.

Before a clay flue liner will melt, it will mostly likely crack (see Elk's post above about the condition of flue tiles after a recent chimney fire). This is due to the clay flue liner's geometry, susceptibility to cracking from its poor thermal shock (fast heat/cool thermal cycling) properties and its low coefficient of thermal expansion.

Aye,
Marty

Grandma used to say, "It's the little things that can make the difference."