Porcelain finish "crazing"

[PA. Woodsman]

Last season I had noticed about a quarter-sized area on the top of my woodstove where the porcelain finish had "cracked", so I removed all of the loose paint and filled in the space with touch-up paint. I was told that this cracking effect is called "crazing" and is quite common with porcelain finishes. I'm just wondering why it only happens on certain areas-this is the top-rear of the stove, near where I have a steamer sitting. I also noticed that I can make out the backwards words "Vermont Castings" on the stove where the steamer sits-it actually somehow imprinted itself on the stovetop from the lettering on the steamer! I hope that this crazing stays limited to a small area of the stove. Any comments would be appreciated-thanks!

 

[EngineerDude]

Woodsman,

The term "crazing" generally is used to describe small cracks in a ceramic outer coating. As it would relate to the ceramic coating on a woodstove, this could result from a mismatch between the thermal expansions of the ceramic coating and and the (cast iron? steel?) body to which it's attached. In a common usage of the term, crazing would bring to mind widespread cracks, in a relatively consistent pattern. Frequently this is done on purpose, for esthetic purpose. The term would not be generally used to describe the phenomenon of a large piece of ceramic chipping off while the surrounding material remains.

Bottom line on use of the term, I personally wouldn't use this word to describe what you've observed on your stove.

Irrespective of what we call it, the failure of the bond between the ceramic and the metal can be due to the thermal expansion problem described above (materials expanding at different rates as the temperature changes, and the relatively brittle ceramic gets to a point where it can't handle the stress), or it could be simply a bad application of the ceramic. On this latter explanation, I don't have deep expertise in materials science, but from what I do know, it could be sub-standard ceramic material quality, improper surface preparation, inproper firing of the ceramic, the wrong ceramic chosen for application with that particular metal, etc., etc.

You don't state the age of the stove. Still under warranty? If so, I'd be back at the manufacturer real fast. Without knowing more, it's impossible to really conclude this, but I would suspect that this is not the last problem you're going to have.

 

[PA. Woodsman]

Woodsman,

The term "crazing" generally is used to describe small cracks in a ceramic outer coating. As it would relate to the ceramic coating on a woodstove, this could result from a mismatch between the thermal expansions of the ceramic coating and and the (cast iron? steel?) body to which it's attached. In a common usage of the term, crazing would bring to mind widespread cracks, in a relatively consistent pattern. Frequently this is done on purpose, for esthetic purpose. The term would not be generally used to describe the phenomenon of a large piece of ceramic chipping off while the surrounding material remains.

Bottom line on use of the term, I personally wouldn't use this word to describe what you've observed on your stove.

Irrespective of what we call it, the failure of the bond between the ceramic and the metal can be due to the thermal expansion problem described above (materials expanding at different rates as the temperature changes, and the relatively brittle ceramic gets to a point where it can't handle the stress), or it could be simply a bad application of the ceramic. On this latter explanation, I don't have deep expertise in materials science, but from what I do know, it could be sub-standard ceramic material quality, improper surface preparation, inproper firing of the ceramic, the wrong ceramic chosen for application with that particular metal, etc., etc.

You don't state the age of the stove. Still under warranty? If so, I'd be back at the manufacturer real fast. Without knowing more, it's impossible to really conclude this, but I would suspect that this is not the last problem you're going to have.

Thank you for replying to my question. There is an area on the top rear of the stove that is about 6" by 3" that is "crazing" (if this term is applicable)-it is cracking and you can see lines in it all over that area. The area that I had to repaint came off in pieces and exposed the cast-iron stove surface. I 'm thinking the same thing-eventually ALL of these little cracked pieces will loosen up and peel off and I'll have to touch it up. I'm thinking along the lines of you, that it probably for whatever reason was not applied as strongly there, and will continue to do this. I just hope that it stays confined to this small area on the top and doesn't want to spread. The stove is a 1993 Dovre Aurora, so the warranty has long run out-plus they were bought out several times over the years. I just hope that this will stay a "small" problem-I have no idea how I would repair it if the whole top went bad; I guess that I'd have to take it somewhere and get it sandblasted and re-enameled? I'll keep after it the best that I can; thanks again for your time and thoughts!

 

[PA. Woodsman]

Addendum...

On a related note, last night I noticed that there was a decent sized chip of porcelain missing from the top of my lattice steamer. Now this is at a spot where I know for certain that was not bumped, dropped, etc. So I guess that what we said before about "weak spots" and weak bonds of the porcelain coating are true-I see no other way that this would've chipped off!