Soft brick wash recipe

[GwynneH]

Hi!  Looking for recommended soft brick wash/coating for a soda kiln constructed from a retired electric.  I have a bag of crystalline silica to start.  Is it recommended to mix this with anything other then water before application?

 

Thank You!

[Mark C.]

I would not use that silica at all

50% Alumina
50% Kaolin
this is a basic salt kiln wash

The 50% alumina is at a good start I also like some milled zircon

The kaolin makes it stick

So maybe 50 alumina Hydrate and 20 Milled zircon and 30 EPK

silica is not to be used in this wash at all-soda and salt go after it (stick to it like the silica in the clay pots)

water it down to thick cream-spray the soft bricks just befor applying as they will suck all the water out of wash if not a little damp 1st. One thin coat is far better than a thick coat which tends to spall off later. Keep  that coat thin .

 

[Kelly in AK]

1 hour ago, Mark C. said:

silica is not to be used in this wash at all

No silica!

I had the good fortune of getting a large amount of zircopax cheap, more than I could ever imagine using for glazes. I used a mix of 40% kaolin and 60% zircopax in my soda kiln (built from a hodgepodge of old electric kiln bricks). It certainly extended the life of the bricks, places that weren’t coated deteriorated faster. It fired hard, sturdy. Alas, there is no coating that will last indefinitely.

 In my case bricks from different kilns were mixed and some spalled sooner than others. That kiln had somewhere around 30 cone 6 soda firings before large chunks of the wall began peeling off. Soft bricks all spall eventually in soda. I rebuilt it this summer with new k-26 brick, used the same coating, dipping each brick before laying it. The places that get hit heavy are made from hard brick, and I have kiln shelves lining parts of the walls too.  

As Mark mentioned, it’s best to wet the bricks before applying. You’ll get a much better coating. 

[Bill Kielb]

I would agree with all and add that traditional wadding (50/50) has more than enough silica from the kaolin. I have even tried refractory coatings (ITC). In the end, salt soda eats away at everything.  I will say the bonded nitride shelves were better than the old silicon carbide. I don’t believe the nitride were recommended for that use at the time though.

I would have to count but that kiln probably had 20-30 ( mostly cone 10 soda with reduction - if ya wanted it) firings on it with regular patch type maintenance. I think with diligence that old Alpine could go 50 - maybe even 75 or more firings actually. All depending how diligent the maintenance of course.

Removable reduction mostly saved the O2 probe.

Edited January 30, 2023 by Bill Kielb

[neilestrick]

Soda/salt does not attack silica on its own. Plain silica is quite resistant to salt/soda effects. It's the silica/alumina/salt eutectic that causes the glaze to form. We used to dust silica onto the shelves for salt firings instead of using wash. That said, I would use a high alumina wash as stated. I think a 50/50 wash is more likely to shrink away and flake off, though, so I would calcine half the kaolin.

[Mark C.]

(calcine half the kaolin) Yes I forgot to mention this as well. Its what I do with my kiln wash for shelves .Same formula 50% alumina 25% calcined Kaolin and 25% kaolin