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Seedy Potter

Solutions For Flaky Kiln Wash

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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????

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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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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!

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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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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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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

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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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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!

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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?

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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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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.

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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.

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i agree that it sounds like your wash is simply applied too thick.

 

we also use a 50/50 epk/silica wash on our electric kiln shelves and don't really have any issues, the key is to keep up on good kiln wash maintenance/application.  we don't even use calcined material.  i've noticed the key is to not apply too thick in one layer and to make sure you rub off the flaky parts of the old layer with a rub brick before rewashing.  sure it's slightly more messy and time consuming to do this, but since this wash sticks "just enough" and yet easily comes off, it makes sense for us since the wash doesn't build up with repeated coats - which leaves a huge divot when a chunk comes off.  it also promotes our students good studio habits to clean and rewash the shelves every time they load/unload a kiln.

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Norm;

As much as I love Bentonite,  [to keep glazes in suspension], I wouldn't be putting it into kiln wash.

There are two types of kiln wash;

For salt soda and wood;

Alumina Hydrate 50 %

Kaolin                 50%

 

For electric kilns and gas kilns you use the following;

Kaolin   50

Flint      50

 

Keep these shelves away from your salt kiln as Flint/silica is a glass former.

Alumina hydrate is expensive and not necessary for electric.

Why are you adding fritt to your kiln wash? It is also a glaze former, and also expensive and heavy in a solution.

You don't need to be deflocculating anything. This is kiln wash we're talking about here.

Keep it simple.

TJR.

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I agree with justanassembler and Mark C.  -   Alumina Hydrate is Kiln Wash. I add just 5% to 10% kaolin or bentonite.

 

I also add Propylene Glycol to the water making application smoother and uniform, and I also stole Jeff Canpana's idea of using Darvan to make the kiln wash into a slip a couple of years ago - but you have to get used to the concept of kiln wash as a slip rather than a suspended glaze.

 

Silica does not belong in Kiln Wash, especially not 50%.  Silica is a glass-former. Glaze runs on a silica kiln wash provides all the flux needed to make your silica kiln wash into a glazze, leaving you using with a chisel and a hammer.

 

Some add 1% feldspar to keep kiln wash on the shelf, but this is more for ^10.  I add 1% Ferro Frit 3124 for ^6 kiln wash.

 

Dusting a shelf with extra alumina hydrate under the work of an amateur glazer can be a miracle.

 

That's some expensive kiln wash there. Silica can be used in kiln wash just fine. It is refractory, and far less expensive than alumina.

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