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LilyT

soft brick coating for salt and wood fire

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hi, all!

 

Looking for advice from you all on use of coatings for

soft brick used to line a kiln for soda and wood firing, but

the kiln will also use propane to help heat it and provide

some air movement for better oxygenation.

Does anyone here have any experience on what might

be useful or a waste of time/money/effort? I am

hoping to have a kiln with hard brick on the floor

and top but save mass and increase insulation by

using soft brick on the mid to upper walls. Can this

work to have a reasonable lifespan? Am I crazy?

Ignorant? Both :-).

 

I saw that Mark C. had some comments about

colloidal silica and zircon flour (on Clayart) a while

back, so maybe he can chime in, too, on his experience

and whether it may or may not help in this case?

I am seriously confused as to whether coatings help

bind together soft brick or prevent vapor penetration

or maybe something else altogether different, so

any education in this matter would be gratefully

accepted.

 

Any information, recommendations, clues would

help.

 

Thanks!

-Lily

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Lily

This should cover it

http://ceramicartsdaily.org/community/topic/2248-crumbling-soft-brick-in-kiln/

I do not use this in the salt kiln -I use it in the bag walls and walls in the heat trench and in burner ports and on fiber in those areas on my reduction gas kilns.</div><div>The best use of the zircon is to keep bricks from spalling it sticks to them and stays its good for soft brick to hold it together

As its a silica binder it will not be good in a salt environment as salt sticks to high silica items like shelves and bricks

Things that have more alumina work better in salt kilns to resist.

For the heat of a wood kiln firebox this zircon stuff would be idea-I have not used it much above a bagwall height. Soda to me seems very Benin compared to salt and I have not been around it much.

In my salt we used ITC on soft brick and I have my own proprietary coating I'm developing for such use and have been using that.

Mark

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We used a zircon flour/colloidal silica coating in grad school to coat the soft brick doors on our salt and soda kilns. It worked great. Zircon is very resistant to salt/soda vapor. I used to use a zircon flour and EPK mix for wadding.

 

The salt/soda glaze will not form without alumina present in the mix, too, which is why you can actually just dust flint on the shelves to protect them during the firing.

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Here is a basic salt kiln wash-no silica in this

http://ceramicartsdaily.org/firing-techniques/soda-firing/the-many-layers-of-kiln-wash-how-to-find-the-best-kiln-wash-for-your-firing-temperature-and-methods/

 

We make our wading from 50/50

Alumina and EPK-it comes off easy in heavy salt.

Mark

post-8914-134342052877_thumb.jpg

post-8914-134342052877_thumb.jpg

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Thanks, Mark and Neil, for taking the time to help me out! This subject makes my

brain hurt every time :-).

 

Let's see if I'm understanding correctly here...

 

Vapor glazing reactions occur when fluxes land on the silica, so I should use

higher alumina products (e.g. alumina) or items with silica that have higher

melting temperatures (e.g. zircon) even when they have silicates in them

(zircon, EPK). Some fluxing can even be your friend, as in John Britt's modified

kiln wash where he adds 1% feldspar, so that materials don't lift off the

kiln and stick onto your pots.

 

However, salt (sodium, calcium, or potassium) and silica also won't form glaze

unless there is some alumina too, so I can use a pure silica (flint) material to help

shield surfaces.

 

Neil's experience that colloidal silica/zircon does actually protect kilns is useful data.

As is Mark's experience with ITC.

 

So my issue with soft brick (made of alumina and silica) where the hot face

fluxes (due to ash deposition and soda/salt) and eventually spalls off when

it's penetrated about 3/16 inch into the brick, can be moderated

by adding a coating that sticks to the brick surface (i.e. fluxing in) but having a

close enough coefficient of thermal expansion such that it does not want to fall

off during temperature shifts. (and not using soft brick on the roof)

 

And thanks, too, for mentioning the wadding choices! I have not tried zircon

in the wadding, though we have used the other recipes. I will try some.

 

The photos of Mark's gorgeous pots unloaded safely were great. I have

fired a combination of soda and wood, and I am wanting to try just soda

and just salt eventually. I think our wadding problem is due to the

sheer amount of ash being so heavy in some areas that a large flood of glass sticks

the pot to the shelf/floor (and breaks the pot as it cools). Bigger wadding may

be the answer, or more control in the firing, or maybe using soft brick as the wadding.

I recently saw some *beautiful* seashell markings from filled shells used as wadding.

(Big seashells. Little marks. Sorry, I digress)

 

So I will try the colloidal silica / zircon on the lower portions of the kiln, and

consider painting it on the upper (soft brick, K26) areas too. It sounds like this

could be applied even to previously used (but not friable) surfaces, which is

good because I am using old hard brick (but new soft brick).

I haven't had as good luck with alumina based kiln washes (mixed with calcined and raw EPK) staying on (and

conversely when used thinly, the kiln shelf fluxes anyway) so I'll put

that on the back burner for now, so to speak. It may be something in

the way I'm applying it (or that I need to use the feldspar), so I'll think

about it.

 

I am curious about the sand layer, but that probably wouldn't stay put with

the rate of air flow by the top end of the firing.

 

 

Does this make sense? Have I used your advice correctly?

 

Thank you so much!

warmest regards,

Lily

 

As an aside, I was reading Euan Craig's blog recently and it seems he just lets the

soft brick get crusty (maybe he scrapes off the worst )and things just keep

working for upward of a hundred firings (that's enough for me, but

for you guys it's only a couple years, eh?) That's something to think about, too.

 

 

P.S. #2

I was also curious as to how high Mark's bagwall (mentioned in regard to the

zircon coating) is compared to the full height of the kiln?

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Thanks, Mark and Neil, for taking the time to help me out! This subject makes my

brain hurt every time :-).

 

Let's see if I'm understanding correctly here...

 

Vapor glazing reactions occur when fluxes land on the silica, so I should use

higher alumina products (e.g. alumina) or items with silica that have higher

melting temperatures (e.g. zircon) even when they have silicates in them

(zircon, EPK). Some fluxing can even be your friend, as in John Britt's modified

kiln wash where he adds 1% feldspar, so that materials don't lift off the

kiln and stick onto your pots.

 

(Wikapedia

Salt glaze pottery is stoneware with a glaze of glossy, translucent and slightly orange-peel-like texture which was formed by throwing common salt into the kiln during the higher temperature part of the firing process.Sodium from the salt reacts with silica in the clay body to form a glassy coating of sodium silicate. The glaze may be colourless or may be coloured various shades of brown (from iron oxide), blue (from cobalt oxide), or purple (from manganese oxide).[1][2][3]

However, salt (sodium, calcium, or potassium) and silica also won't form glaze

unless there is some alumina too, so I can use a pure silica (flint) material to help

shield surfaces.

 

Neil's experience that colloidal silica/zircon does actually protect kilns is useful data.

As is Mark's experience with ITC.

 

( I have had great experiences with ITC sprayed on soft brick in salt kiln-this coatings sprayed on damp bricks-in salt kiln)

( our k28s do spall over time but these coating help extend the life)

 

So my issue with soft brick (made of alumina and silica) where the hot face

fluxes (due to ash deposition and soda/salt) and eventually spalls off when

it's penetrated about 3/16 inch into the brick, can be moderated

by adding a coating that sticks to the brick surface (i.e. fluxing in) but having a

close enough coefficient of thermal expansion such that it does not want to fall

off during temperature shifts. (and not using soft brick on the roof)

 

And thanks, too, for mentioning the wadding choices! I have not tried zircon

in the wadding, though we have used the other recipes. I will try some.

 

The photos of Mark's gorgeous pots unloaded safely were great. I have

fired a combination of soda and wood, and I am wanting to try just soda

and just salt eventually. I think our wadding problem is due to the

sheer amount of ash being so heavy in some areas that a large flood of glass sticks

the pot to the shelf/floor (and breaks the pot as it cools). Bigger wadding may

be the answer, or more control in the firing, or maybe using soft brick as the wadding.

I recently saw some *beautiful* seashell markings from filled shells used as wadding.

(Big seashells. Little marks. Sorry, I digress)

(

We have used shells but they fluxed more than we liked)

 

So I will try the colloidal silica / zircon on the lower portions of the kiln, and

consider painting it on the upper (soft brick, K26) areas too. It sounds like this

could be applied even to previously used (but not friable) surfaces, which is

good because I am using old hard brick (but new soft brick).

I haven't had as good luck with alumina based kiln washes (mixed with calcined and raw EPK) staying on (and

conversely when used thinly, the kiln shelf fluxes anyway) so I'll put

that on the back burner for now, so to speak. It may be something in

the way I'm applying it (or that I need to use the feldspar), so I'll think

about it.

 

I am curious about the sand layer, but that probably wouldn't stay put with

the rate of air flow by the top end of the firing.

 

 

Does this make sense? Have I used your advice correctly?

( for us we try to avoid silica products in slat kiln-like silicon carbide shelves or posts which always get tons of drips on them-we use dry pressed high alumina English shelves coated with ITC as well-we sprayed out pots with itc-we spayed our fiber door and hard and soft brick walls and Roof (fiber) with iTC-it resists salt very well-We do use alumina in wading and avoid silica in all our recipies (home made kiln wash)

Thank you so much!

warmest regards,

Lily

 

As an aside, I was reading Euan Craig's blog recently and it seems he just lets the

soft brick get crusty (maybe he scrapes off the worst )and things just keep

working for upward of a hundred firings (that's enough for me, but

for you guys it's only a couple years, eh?) That's something to think about, too.

 

I added comments about to your text-I only have fired this salt kiln about 10 fires so far.

P.S. #2

I was also curious as to how high Mark's bagwall (mentioned in regard to the

zircon coating) is compared to the full height of the kiln?

 

(My bag wall in salt kiln is 4 bricks high on the 4 1/2 edge loosely stacked so thats 18 inches tall

Remember In the salt I have yet to spray the zircon mix-I only have used it in reduction firing kilns.

I will test in next salt fire next year.)

Heres the salt kiln when it was NEW

http://ceramicartsda...__fromsearch__1

Mark

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... <lots of great comments elided out temporarily as my sister's kids are coming over

soon and I gotta get the house straightened up, but I couldn't resist a quick reply>...

 

(My bag wall in salt kiln is 4 bricks high on the 4 1/2 edge loosely stacked so thats 18 inches tall

Remember In the salt I have yet to spray the zircon mix-I only have used it in reduction firing kilns.

I will test in next salt fire next year.)

Heres the salt kiln when it was NEW

http://ceramicartsda...__fromsearch__1

Mark

 

 

Mark, thanks for your comments, I promise to think about it and get to them soon!

 

 

-Lily

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... <lots of great comments elided out temporarily as my sister's kids are coming over

soon and I gotta get the house straightened up, but I couldn't resist a quick reply>...

 

(My bag wall in salt kiln is 4 bricks high on the 4 1/2 edge loosely stacked so thats 18 inches tall

Remember In the salt I have yet to spray the zircon mix-I only have used it in reduction firing kilns.

I will test in next salt fire next year.)

Heres the salt kiln when it was NEW

http://ceramicartsda...__fromsearch__1

Mark

 

 

Mark, thanks for your comments, I promise to think about it and get to them soon!

 

 

-Lily

 

 

Lily

I have done a lot of testing with this but recently learned that its best not to talk about testing so just forget any thing that I may have said about testing.I guess its best now for folks to make their own mistakes and not take advise from others.Heck I know very little on this subject-I've only been coating things for 25 years now.When I get better at it I'll post again.

Mark

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... <lots of great comments elided out temporarily as my sister's kids are coming over

soon and I gotta get the house straightened up, but I couldn't resist a quick reply>...

 

(My bag wall in salt kiln is 4 bricks high on the 4 1/2 edge loosely stacked so thats 18 inches tall

Remember In the salt I have yet to spray the zircon mix-I only have used it in reduction firing kilns.

I will test in next salt fire next year.)

Heres the salt kiln when it was NEW

http://ceramicartsda...__fromsearch__1

Mark

 

 

Mark, thanks for your comments, I promise to think about it and get to them soon!

 

 

-Lily

 

 

Lily

I have done a lot of testing with this but recently learned that its best not to talk about testing so just forget any thing that I may have said about testing.I guess its best now for folks to make their own mistakes and not take advise from others.Heck I know very little on this subject-I've only been coating things for 25 years now.When I get better at it I'll post again.

Mark

 

 

Hi, Mark,

Fancy seeing you here on this thread, too :-). Oops, I lost track of which threads

I'd replied to. (I've taken to mostly typing on my editor and pasting it in, but I have

literally >1000 windows open due to work etc and got lost). You sound like you

feel someone is disregarding your opinions - I hope it was not something I said that

may have inadvertently offended you!- I am doing my best to understand a difficult

subject where I am a beginner so forgive me if I misinterpreted or didn't give enough

weight to something you said.

If you still don't mind continuing this conversation, what I think I took away

from your illuminating comments was that ITC on soft brick protects, so I have

ordered the ITC and plan to use it there. I have changed my kiln design to have more

soft brick therefore, since this will make it need fewer makeovers and also lower

the energy requirements.

You said your seashells fluxed too much... were they just stuck then? Or did

the pots just sink through the shells?

I am not sure what to do with my shelves, lol, I had gotten all silicon carbide already

to start with (I had a bunch of shelves and some brick, and it occurred to me that

it could become a kiln). I guess if they get all eaten up, then I'll replace them with

alumina. Or maybe I'll stick to wood at first.

I will spray the posts (brick) with ITC, that's something I hadn't originally

thought about, thank you.

And perhaps I will put the colloidal silica/zircon mix in half the bottom of

the kiln (hard brick).

My goodness. This kiln will have such good parentage. I wish I could do

something to thank you and everyone for such kind help. Suggestions? Firing

party?

 

warmest regards,

Lily

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... <lots of great comments elided out temporarily as my sister's kids are coming over

soon and I gotta get the house straightened up, but I couldn't resist a quick reply>...

 

(My bag wall in salt kiln is 4 bricks high on the 4 1/2 edge loosely stacked so thats 18 inches tall

Remember In the salt I have yet to spray the zircon mix-I only have used it in reduction firing kilns.

I will test in next salt fire next year.)

Heres the salt kiln when it was NEW

http://ceramicartsda...__fromsearch__1

Mark

 

 

Mark, thanks for your comments, I promise to think about it and get to them soon!

 

 

-Lily

 

 

Lily

I have done a lot of testing with this but recently learned that its best not to talk about testing so just forget any thing that I may have said about testing.I guess its best now for folks to make their own mistakes and not take advise from others.Heck I know very little on this subject-I've only been coating things for 25 years now.When I get better at it I'll post again.

Mark

 

 

Hi, Mark,

Fancy seeing you here on this thread, too :-). Oops, I lost track of which threads

I'd replied to. (I've taken to mostly typing on my editor and pasting it in, but I have

literally >1000 windows open due to work etc and got lost). You sound like you

feel someone is disregarding your opinions - I hope it was not something I said that

may have inadvertently offended you!- I am doing my best to understand a difficult

subject where I am a beginner so forgive me if I misinterpreted or didn't give enough

weight to something you said.

If you still don't mind continuing this conversation, what I think I took away

from your illuminating comments was that ITC on soft brick protects, so I have

ordered the ITC and plan to use it there. I have changed my kiln design to have more

soft brick therefore, since this will make it need fewer makeovers and also lower

the energy requirements.

You said your seashells fluxed too much... were they just stuck then? Or did

the pots just sink through the shells?

I am not sure what to do with my shelves, lol, I had gotten all silicon carbide already

to start with (I had a bunch of shelves and some brick, and it occurred to me that

it could become a kiln). I guess if they get all eaten up, then I'll replace them with

alumina. Or maybe I'll stick to wood at first.

I will spray the posts (brick) with ITC, that's something I hadn't originally

thought about, thank you.

And perhaps I will put the colloidal silica/zircon mix in half the bottom of

the kiln (hard brick).

My goodness. This kiln will have such good parentage. I wish I could do

something to thank you and everyone for such kind help. Suggestions? Firing

party?

 

warmest regards,

Lily

 

 

You may want to ask Offcenter as he has vast wood firing experience and they coat those kilns.

John Baymore also has lots of this behind him-he has the most experience here and I respect him and what he says.

I only have 35-40 years of it so I;m a newby still testing and learning .

Mark

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