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Undersides Of Shelves Glossing, Blistering And Flaking.


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#1 Babs

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Posted 19 August 2014 - 07:52 PM

As the title says, my shelves have been fired many times, never kilnwashed on the sides and undersides but lately they have been blistering and this has cracked and flakes during firing, revealing the rough interior. If I grind these it will be the " guts ' of hte shelf which will be facing the grinder, is this the way to go?



#2 neilestrick

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Posted 19 August 2014 - 09:08 PM

What kind of shelves? What kind of kiln/firing?


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#3 Babs

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Posted 19 August 2014 - 09:49 PM

well I fire an electric kiln and don't know the trade name for these shelves but they are cream coloured! common garden stuff. Not modern state of the art. I'm firing midrange now but these shelves  have been to c10 in their lifetime. Not near my paper stuff today or I could get a brand, Aus. though.



#4 Mark C.

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Posted 19 August 2014 - 09:50 PM

How about a photo of the flaking bottoms ?

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#5 Babs

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Posted 19 August 2014 - 09:59 PM

Sure when i get back to my place.



#6 Mark C.

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Posted 19 August 2014 - 10:11 PM

My guess without seeing them is use a 4 inch grinder and smooth them up-dust them off and call it good.

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#7 Babs

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Posted 20 August 2014 - 04:22 AM

Attached File  Photo0384.jpg   29.06KB   0 downloads

Attached File  surface of shelf lifting.jpg   20.13KB   0 downloads

here is the shelf undersurface. This one has been progressing for a time, also this one, making a fibber of me has been lightly kiln washed. the other shelves are still in my killn, unloading tomorrow



#8 Wyndham

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Posted 20 August 2014 - 08:40 AM

Kiln wash will gloss out and flake over time if you don't sand/grind/clean the shelves.

I have used a portable belt sander to  clean off old kiln wash.

https://www.google.c...x-a&channel=nts

 

It's the second set of images on the page

 

Wyndham



#9 Mark C.

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Posted 20 August 2014 - 10:34 AM

Sand or grind it smooth is what I would do.

Mark


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#10 Babs

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Posted 20 August 2014 - 05:55 PM

It'll be a grind as this is rough stuff exposed.



#11 neilestrick

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Posted 20 August 2014 - 06:16 PM

I can't tell anything from the photos! :rolleyes: It's odd that kiln wash would gloss and blister. Are you sure it was kiln wash and not something else?


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#12 Mark C.

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Posted 20 August 2014 - 06:59 PM

Thew photos do not show much.

The 4 inch grinder with masonary or diamond blade-I would go masonary as its a bit slower cutting.

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#13 Babs

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Posted 20 August 2014 - 08:27 PM

OK, OK Cheap phone here!!, or clay on your glasses Neil :D

My prob  with grining is that the smooth ground surface of the shelves seems to be lifting and flaking to expose a really rough interior.

I'll post better photos today as I unpack.

i've heard of shelves becoming glssy on underside but  this is electric firing ..

The second photo was trying to show the lifting of  the surface of the shelf  ...



#14 High Bridge Pottery

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Posted 20 August 2014 - 09:05 PM

I thought kiln shelves were a solid thing, not an outer and inner layer but I also thought there was only one type of shelf till a few months ago. 



#15 Babs

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Posted 20 August 2014 - 09:14 PM

Attached File  blister.jpg   55.94KB   0 downloads

Attached File  flaking shelf.jpg   61.23KB   0 downloads

Hopefully more evident. In upper left corner one can see??? the shelf surface which has been "protected' by the support ie original surface of shelf albeit pitted and gunked by unwashed kiln furniture, can't remember the proper word at the mo and I know you guys will hunt me down if i use post instead of some other esoteric word. :D

This shelf has had no kiln wash on this surface.

My kiln does bump up incredibly if placed on high as I have been known to do. Would this be a cause?



#16 Mark C.

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Posted 20 August 2014 - 11:22 PM

This is some type of coating as best as I can tell-

looks like a thick layer of washes.

 

(I thought kiln shelves were a solid thing, not an outer and inner layer but I also thought there was only one type of shelf till a few months ago. )

Shelves come in many different types and most here on this forum ask about their electric ones as one type-a 1/2 inch mullite with several sides that fit electric kilns

But wait theres more than one type-really

 

Mullites are cheap and thats what most use in electrics I have found

But their are many types and many thicknesses
They come in hollow core coralites (lighter stronger) which are like honeycomb insides that are hollow.
These also come in standard 12x24 or larger sizes and thickness for higher temps
There are the old standard silicon carbides which where the best when I came into ceramics 3/4 inch was the thing back in the day
Then came the dry pressed high alumina English shelves that I replaced all my older warped siclicon carbides with mine where all 1 inch and warped way less at cone 11 they weigh 30#s each.
Then came the recyristalized silicon advancers that NEVER warp or change and are just over 1/4 inch thick and a 12x24 wieghs 9#s
then the cheaper knock offs from China-I have one on kiln floor thats warped and cracked right now.These are not the same as advancers really.
So when you talk about shelves everyone its best to say what kind you are talking about?
Now as for Babs she is in Australia and I have no idea about that material over there (I have visited Aus but saw zero shelves but did do the Sidney Bridge climb 10 years ago) but have a strong sense its Mullite and there are mullite all the way through except for that coating someone applied and is now peeling off.
Mark

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#17 Babs

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Posted 21 August 2014 - 02:38 AM

Never had wash on it Mark that is why I am bamboozled. Somestuff must be vapporising and coating the shelves.



#18 neilestrick

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Posted 21 August 2014 - 08:32 AM

Much better photos! That's definitely not normal behavior for a kiln shelf. Either some vapor is getting to them or there was something wrong in their original formula or something was put on them that wasn't wash. How long have you been using these shelves? I would replace them, not mess with grinding.


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#19 oldlady

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Posted 21 August 2014 - 10:23 AM

babs, these shelves look just like the ones i was given with an older kiln.  i also suspected some kind of vaporizing.  i tried scraping, did not work.  took the shelf to an expert in  the business of grinding various surfaces.  told him to try anything.  he did and called me to say it would not come off and he did not want to try anything else on them.   i got new ones.  before that, they dropped junk all over whatever was below them during firing.

 

kiln furniture is simple.  posts hold up shelves. they come in various shapes, my favorite is a triangular post with a central hole because they take less room.  there are square ones, odd shaped ones and some, usually used in wood or gas firings are called soaps or half soaps.

 

someone recently wrote a book and incorrectly put the word "stilts" in place of the word "posts".   stilts are actually the things that are used to raise lowfire glazed earthenware off the shelf to protect the ware from sticking to the shelf.  they sometimes have metal prongs sticking up from a ceramic base and leave tiny pinpoint marks stuck in the glaze on the bottom of earthenware.  some stilts are made with all ceramic materials with pyramidal points to support the ware.  these can be very sharp if broken off the bottom of a piece after firing.

 

sorry you need to replace your shelves, it is a real expense.


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#20 Babs

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Posted 21 August 2014 - 07:07 PM

Thought as much. :(

The shelves are very old.

Was going to ask if it would be better to use discs for concrete/cement, or stone and cast on grinder , but from the above seems like it would be a waste of time.

Dilemma now as the kiln is so old and unless I purchase a new one with same dimensions I'll be sinking money with no return.

Old lady,Thanks for the definitions re kiln furniture, my nouns get lost, not dementia been like it all my life.

For time being I'll grind around the edges of break in surface and hopefully keep the edges from dropping on ware below.....

Thanks everyone.






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