Jump to content


Member Since 08 Aug 2013
Offline Last Active Jan 16 2017 06:09 PM

Posts I've Made

In Topic: Fractured Kiln Shelves...

16 January 2017 - 03:10 PM

Mike In ceramics often things work until (even thought not done right) until one pushes the limit -such as your fast fire.

It does matter that all posts are under one another from the floor to the ceiling. You may get away with this for years but sooner or later it will get you .

Wadding is EPK and alumina hydrate mixed 50% 50% with a little water.

next time make sure all pots including under floor all always lined up-the wadding as on under floor pots only to level. fire the 1st time a bit slower to dry wadding .

I will speak to your pots layout only after I know what you use above that full shelve ? all full shelves or some 1/2 shelves??


We use full rounds all the way up the stack. We use to use halves, but when I'm firing a full load of Rocks cups, I need every single cubic inch I can get. We use a 3 post arrangement between shelves. In bisque I allow a 1/2" space between the rim and the bottom of the next shelf, except when I get to the thermocouple. I make sure there we have enough vertical space to provide 2" of clearance on all sides of the thermocouple. 

In Topic: Fractured Kiln Shelves...

16 January 2017 - 03:04 PM

Is the shelf always the bottom shelf? Could it have been warped before the fast firing? I'm thinking if there were additional supports under the shelf, which must be the case or the shelf would have dropped, then an uneven support would add to the stress on this shelf. Always under the assumption that the 3 posts were the most effective and efficient way to stack...
Are your posts needing replaced/ground.. remembering an article by Mark..
How are all these comments tracking in your brain Mike?



I loaded it myself, the only reason I recently loaded it was because the first and much older shelf fractured. That shelf had been the floor shelf since 2013. It was only removed to replace the elements and vacuum the kiln. 


I suppose the stresses building up over time would explain the first fracture, but what about the second? It happened on the first fire.


There was no signs of warpage when I loaded it, and I did check to see if there was a wobble, and there was none. Now, our posts have some miles on them, and they have been dropped and knocked around. So, it is entirely possible we had a post that was no perfectly level. Plus we had some pots blow from too much moisture a few days ago, so there could have been some debris that wasn't completely cleaned out from the kiln. I did find some bisque shards, but nothing under the spacers, when I cleaned out the shelf.


It's possible the posts need to be replaced. I'll do that as precaution, and check them over to see if they need to be ground. Good suggestion...


This good stuff, I'm learning a lot...  No one ever told me how post the spacers when setting up a kiln. If I can get by with just 3 that would be nice.

In Topic: Fractured Kiln Shelves...

16 January 2017 - 02:55 PM

so I think you said you added for posts under the bottom shelf around the center. Were there 3 outer edge posts to support the ones supporting the shelves as well?
If you had 7 posts under the bottom shelf, it could be some were slightly different in height and stressed that she enough to crack it.



Here is the configuration of spacers on the first fracture:


                                X           X



     X                                                           X


     X                                                           X



                               X           X


Keep in mind, that configuration was in place since 2013 without incident... After the first shelf broke, I modified the spacer patter as follows:



                               X           X




     X                         X        X                      X


     X                         X        X                      X




                               X           X

The second shelf split on the first fire of this config... It was a newer shelf, much newer. 

In Topic: Fractured Kiln Shelves...

16 January 2017 - 02:49 PM

Are the 3 posts on the top of the shelf aligned with 3 corresponding posts underneath the shelf?


Additional posts generally don't help, they just cause the shelf to rock which creates a lot of stress points.


A shelf that large may not be able to handle the really fast heat up unless it's up off the floor to the point that the bottom element groove is under the shelf to throw some heat under there and even it out. A little preheat wouldn't hurt, either.

No, the shelves above are not aligned with the spacers below, but we've been using this post stack for 2 years without incident. If the cause is misaligned force vectors it must be an accumulated fatigue thing. And, if that's the case why would it have happened on the new shelf just as fast and old shelf? 


The fast fire could be causing the negative space above the shelf to heat way faster than the space below. Good Point! We might have to go to a custom fast fire with a hold at the low end of the ramp to allow the bottom to heat up before moving up to the top of the schedule. I would hate to raise the shelf. We fight for cubic inches, to increase our firing yield, every day...


I did not know that more posts brought nothing to the party. I'll try reducing the number of posts and align them with the rest of the posts in the stack. It's worth a test. Thanks!

In Topic: Fractured Kiln Shelves...

16 January 2017 - 02:40 PM


I would use some wadding on the spacers first time you put shelve in to level it all up.

Was this shelve stored on concrete at all for any time before use? or was it always on bottom and the fast schedule was just done and it cracked?

What's wadding? 


Never stored on concrete... 


Recently replaced a shelf that fractured in a firing two days earlier... That shelf was just on the bottom and the fast schedule was run.


This shelf was pulled from a wall rack and replaced the bottom / floor shelf.