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Solutions For Flaky Kiln Wash

kiln wash kiln shelves

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#1 seedy45

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Posted 17 August 2013 - 10:20 AM

I have been working with clay for many years but only firing my own stuff for about 4 years.  I have this recurring problem.  The kiln wash flakes off after every firing - bisque or glaze. (firing bisque at 04 and glaze at 6 in my electric Vulcan kiln) I am constantly cleaning shelves and it seems to be getting worse the more I use these shelves.  I have tried completely removing all the old wash and replaced it with new.  I have tried simply removing the stuff that is the loosest and then washing over it and the surrounding areas.  I've tried thick and thin applications. I am extremely careful with my shelves and do not allow any greasy or oily contamination.  I am using kiln wash that has been mixed for some time (??? years???).  I wouldn't think that's the problem, but maybe....  Anyone have some suggestions????



#2 Chris Campbell

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Posted 17 August 2013 - 10:55 AM

I think it might be too thick. I use mine mixed about as thin as water maybe skim milk.

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#3 Benzine

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Posted 17 August 2013 - 11:12 AM

I agree with Chris.  I've run into the problem before, and it was because I mixed the wash/ applied it too thick.

 

Mix it to the consistency, that Chris suggested, and apply three thin coats.  I alternate the direction of each coat, the first horizontal, then vertical, then horizontal, but I won't say that it's necessary, just my preference. 


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#4 Mark C.

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Posted 17 August 2013 - 11:40 AM

One other point is this wash commercial or homemade-whats the formula?I agree its to thick and needs thining.

Remove all old wash and start over.

Mark


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#5 JohnDonovan71

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Posted 17 August 2013 - 12:00 PM

I have been using a 50/50 silica & EPK kiln wash recipe (by weight), firing the EPK in big bisque-fired bowls before mixing. I also started mixing it much thinner last year, like skim milk thin, and applying 2-3 thin coats. My kiln wash flaking pretty much went away after I made those changes!



#6 neilestrick

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Posted 17 August 2013 - 01:46 PM

If the formula is high in kaolin, like over 20%, you'll need to calcine some of the kaolin. I would leave 10% normal, to help keep the wash suspended in the bucket and make application smoother. To calcine, just put a bunch of kaolin in a bowl and run it through a bisque. Kaolin shrinks when fired, and that's what makes it flake off. By calcining, you pre-shrink it.


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#7 Wyndham

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Posted 17 August 2013 - 02:28 PM

I've had good results with 1/3 silica(325mesh), 1/3 epk,1/3 alumina hydrate, wich does the same or about the same as calcining the epk.

Wyndham



#8 MikeFaul

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Posted 17 August 2013 - 04:26 PM

Hmmmm... Have you tried Jeff Campana's approach?

http://jeffcampana.c...ling-kiln-wash/

A bit more work, but sounds effective. I'm getting ready to try it this week.

#9 Mark C.

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Posted 17 August 2013 - 05:03 PM

Looks like Jeff Campana uses the same recipe

Mine is 

by wieght

50% alumina

25% calcined EPK-(which is called glomax I'm told)-I always make my own

25% EPK

 

I applied this with a roller-two coats

 This was is easy to remove .

 

 

Jeff's is a darvon/ thinner mixture-as my shelves are all flat as a ruler (advancers) I do not bother with this step.

Mark


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#10 Marcia Selsor

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Posted 17 August 2013 - 05:17 PM

I agree with Chris, Mark and others as far as may be a thick application and the suggestion of adding calcined kaolin is good and the addition of alumina hydrate is good. I add about 10-15% and use 50/50 silica/kaolin by volume not weight.
You can make your own calcined kaolin by putting some kaoling in a bisqued bowl and bisque fire it to remove the chemical water.Using this will reduced the shrinkage of the kiln wash.

Marcia

#11 Pres

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Posted 17 August 2013 - 05:40 PM

This seems to pop up often in the forum. If I remember correctly, there was atopic on applying kiln wash about two months ago.

Adding my two cents. Wash is too thick. Mix like skim or 2% milk and apply coats in different directions. Two willusually do.

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#12 seedy45

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Posted 17 August 2013 - 09:43 PM

Hmmmm... Have you tried Jeff Campana's approach?

http://jeffcampana.c...ling-kiln-wash/

A bit more work, but sounds effective. I'm getting ready to try it this week.

Let me know how it works. 



#13 seedy45

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Posted 17 August 2013 - 10:30 PM

Thanks everyone!  I knew there had to be solution/s to this problem that you would be able to help me out with.  I am planning on getting the composition make up of the kiln wash I buy from our local distributor.  I think it has alumina in it, but if it doesn't, I am planning on making my own and calcinating the kaolin.  I will also completely clean my shelves and re-apply 2 - 3 very thin coats of wash.  Thanks again for all your help!



#14 Mark C.

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Posted 17 August 2013 - 10:39 PM

Most commercial washes are cheaply made and are low in alumina or none at all.At least all the ones folks have given me.

Mark


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#15 Benzine

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Posted 17 August 2013 - 11:12 PM

Most commercial washes are cheaply made and are low in alumina or none at all.

Mark

And the alumina is what, really helps prevent things from "Sticking"?


"Anything worth believing, is worth questioning"

#16 justanassembler

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Posted 18 August 2013 - 04:49 AM

 

Most commercial washes are cheaply made and are low in alumina or none at all.

Mark

And the alumina is what, really helps prevent things from "Sticking"?

 

basically, yes.  see: refractory materials.



#17 morah

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Posted 18 August 2013 - 06:12 PM

When you say apply two coats do you fire between each coat, let the first dry before applying the second, or just put on the two coats right away?



#18 Benzine

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Posted 18 August 2013 - 08:38 PM

When you say apply two coats do you fire between each coat, let the first dry before applying the second, or just put on the two coats right away?

You apply one basically after the other.  I usually do several shelves at once, so I'll go horizontal with one coat, on all the shelves, then go back vertically, then horizontally.

 

By the time I get done with the last of each of the shelves, the first coat is set enough.  Kiln wash does dry fairly quick anyway, because the shelving material absorbs the water in the kiln wash.


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#19 morah

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Posted 18 August 2013 - 08:59 PM

Thanks for clarifying. Does it flake less if you bake the newly washed kiln shelves empty or is it fine to put a bisque load on them? I assume a glaze load would be a bad idea on newly washed shelves that haven't been baked.



#20 Benzine

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Posted 19 August 2013 - 07:00 AM

No sense in wasting electricity, just fire the shelves the same time you are firing a bisque.

In a pinch, I have fired the shelves with a glaze load. I didn't have any problems.
"Anything worth believing, is worth questioning"





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