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Cracked kiln shelves


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#1 DallasGypsy

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Posted 25 April 2012 - 04:02 PM

Last week, I bought a used kiln with a huge amount of kiln furniture. A friend helped me transport the stuff and, when I started looking at the shelves more closely, I discovered that about half of them were cracked. The cracks are about three or four inches long from the edge toward the center.


My question is ... can these be used in the kiln or not? Would kiln fix mend them enough to use?


Thanks for your advice.

#2 neilestrick

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Posted 25 April 2012 - 04:36 PM

I've been using some cracked shelves just like those, both cordierite and silicon carbide, for several years. The silicon carbide have warped much more quickly than the non-cracked ones, but the cordierite have not been any worse. There's always the chance that they'll fall in half, but I'm a gambler.Posted Image The cracks are functioning as a stress relief, so unless they get banged, there's a good chance to they'll hold up in the firings. No guarantees, though. You could definitely use one as the floor shelf.
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#3 perkolator

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Posted 25 April 2012 - 05:19 PM

there's not really any fix for this. using them is your choice but is definitely a gamble. don't toss them though, still many uses for a compromised shelf.

in our studio we mainly produce larger-scale sculpture, not lightweight pottery - so when a shelf gets a crack any more than just a short hairline, we'll set it aside for "waste shelves" that will catch an anticipated mishap, or for a very low-weight bearing situations. for shelves beyond this point, I'll break it up into smaller pieces for propping up/elevating work. for us, it's cheaper/extra insurance to just buy a new shelf than to have a stack be compromised and possibly cause LOTS of damage should the shelf fail mid-firing and dump a heavy load onto neighboring shelves/work and/or damage the kiln. also doesn't hurt to have lab fees which help support new furniture purchases when things break.

for pots or similar, you could be ok depending on what goes on the shelf. should you choose to use it, keeping the load over the supports below will definitely help vs loading the weight right over the crack (which would just not be a smart decision :unsure:)

#4 Mark C.

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Posted 25 April 2012 - 05:36 PM

If your kiln load is like this one on my car kiln(photo) I would not use cracked ones near the bottom of stack.
If its mid range electric use I would use them-I assume you are talking about mullite shelves. some tricks are if you can span the crack with a stilt this can help. No amount of miracle glue will help them. They can always just fall into two pieces during a fire-but that said they usually do not
I fired silicon carbide ones that had cracked for many years with no issues to cone 10
As noted in above posts handle them with more care.
Mark

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#5 GEP

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Posted 25 April 2012 - 07:31 PM

One of my cordierite shelves (20 inch round shelves for an electric kiln, glaze fire to cone 6) has a crack just like you describe. I use the shelf all the time, making sure to place the crack on a post. It's been over five years and the shelf has not cracked further or caused any other problems.

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#6 Denice

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Posted 26 April 2012 - 08:26 AM

I used cracked shelves all of the time, I used extra post under it in case it cracks further it won't fall in. To prevent them from cracking further I drill a hole at the end of the crack with a sixteen inch drill bit. Since I have been doing this none of the shelves have continued cracking and it's been 7 years since I started drilling holes. Denice

#7 icyone

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Posted 27 April 2012 - 09:35 PM

Great idea with the drilling holes Denice. Brilliant

#8 DallasGypsy

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Posted 29 April 2012 - 05:52 PM

Thanks for all your input and ideas. I've decided to forego using the cracked shelves and ... if I need more shelves, I'll buy some new ones.




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