crumbling soft brick in kiln

[Sandra Jean]

I was gifted a small gas fired kiln, lined with soft brick that spent it's former life as a wood-soda hybrid kiln. Now, the soft brick inside is falling apart at every touch. Some spots are being held together with old kiln wash, but after my first two bisques and thorough shop-vacuuming, I still have stuff floating around inside. This has not been a problem through bisqueing, but I am ready to glaze fire and fear my pots will be ruined by all this stuff floating around. I would like to eventually buy new bricks to replace the old, but I can't do that before these pots need to be done. This is an unanticipated problem! Time to get creative! I am open to all ideas. One is lining these bricks with kiln cement. Would it, too, flake off?

[neilestrick]

Soda and wood are very hard on soft brick kilns. They deteriorate very quickly. It will continue to fall apart. I don't think you'll find anything that will help it. Nothing will stick to old bricks very well, especially if they're sealed up with a layer of soda and wood vapor. The best you can do is keep your pots packed tight to the shelf above so there's less of a chance of stuff getting in. A protective shelf above the top layer will help, too.

[Sandra Jean]

Soda and wood are very hard on soft brick kilns. They deteriorate very quickly. It will continue to fall apart. I don't think you'll find anything that will help it. Nothing will stick to old bricks very well, especially if they're sealed up with a layer of soda and wood vapor. The best you can do is keep your pots packed tight to the shelf above so there's less of a chance of stuff getting in. A protective shelf above the top layer will help, too.

 

 

 

 

However, even in the bisque, I found particles in wares on the mid-level shelves. I'd like your opinion on the kiln cement idea. If I get a coat on those bricks, will the cement keep them together for the 2-3 firings I need for the upcoming show?

[neilestrick]

Very doubtful on the cement. It won't bind very well to the old brick, and probably won't be thick enough or strong enough to hold if the layer underneath cracks away. I certainly wouldn't trust it with a load of pots until I tested it. Is the surface of the bricks glazed over from the soda and ash? Are the bricks flaking, or a layer of old wash on the surface of the bricks?

[Mark C.]

If it where my kiln and was even thinking about washing it I would make up this which I have used many times. First let me say these products are a bit harder to find and also require application skills-This formula was passed on to me by a glass blower that coats his glory hole on soft brick as well as fiber and I have used it on both.That said here is the deal-

This stuff sticks and stays stays put even in fireboxes.

 

 

You will need some liquid COLLOIDAL SILICA as well as some milled ZIRCON -This is a product Laguna clay carries

The colliidal siica is harder to find-High Temp in Portland carried it at one time.

1 gallon is plenty of the liquid

start out by vacuuming kiln then spray all soft brick with water via a mister bottle so its slightly damp. if its warm out only do the area ahead of your application.

Start with a small say cereal bowl 1/2 full of colloidcal silica about 3/4 cup -This will be your learning curve batch-

add milled zircon powder to this until its like heavy cream (this liquid absorbs a huge amount of powder)-use a wider brush and apply a coat to damp area bricks- coat kiln -let dry then bisque fire.

This mix works as the best coating I have ever seen or used-Its a bit hard to brush and will ruin your bowl and brush but will stick to just about anything-It can be sprayed as well. Work it into all cracks as its acts like a glue as well.

Use a respirator when spraying. It covers my soft bricks and rarely spalls (comes off)

You will not find this pre made and must make your own from scratch.

Good luck-this stuff works. Its about 100% better than any other wash you may want to apply to a kiln.

Mark

[Sandra Jean]

I'm going to try this as soon as I get a chance. The fact that it is cheaper than the cost of new bricks seals the deal.

[DAY]

Throw some saggars?

[perkolator]

interesting recipe....i'm going to have to experiment with that.

 

i would recommend you try out some ITC coating, perhaps ITC-100. apply it pretty much the same way you would the coating mentioned above, with the bricks being pre-wet to help capillary action. stuff is not cheap but works VERY well and is designed for coating and prolonging the lifespan and insulation properties of kilns.

[Mark C.]

The ITC 100 is also a very good coating a bit more spendy but really sticks as well. I sprayed several kilns over the years with it.

Mark

[neilestrick]

I think the hard part is going to be getting stuff to stick to bricks that are old and covered with layers of wash and soda. Every coating I have every used only really worked well on newer, still porous bricks. I'm interested to see how this goes. Keep us posted if you try anything.

[Mark C.]

One thing you could do is sandblast that wash and soda coating lightly then shop vac the whole mess up then proceed with coating.

Mark

[Sandra Jean]

Okay, so here's something new to add to the conversation.

 

I should be clear that the bricks do not show signs of glazing, nothing is shiny or melted looking. The prior owner had kiln washed the inside to make it easier to clean between firings. So, basically, what is crumbling is that layer of kiln wash and some of the exposed brick. The bricks look very porous in some spots. I have removed chunks that were loose, but everytime I pass my hand over the bricks I get what looks like cookie crumbles. I am interested in finding out more about the Colloidal Silica (is this basically sodium silicate?)/Zircon mixture, but have received information stating that it would be too much of a "patch". The ITC is rather expensive (though, not as much as new bricks) and was told buy a kiln repairer that if I am not necessarily interested in improving the insulative value of the kiln, ITC is overkill. His recommendation was to use Rigidizer, which is $30/gallon and should act as the seal I need to keep these brick intact.

 

Any new thoughts on the subject? Not knowing the properties of these different formulas, I feel confused!

[neilestrick]

If your bricks are crumbling, then they're probably just plain old. In order to get them to hold together and harden up with any type of surface application, I'm thinking you'll need to get the layer of wash off first, otherwise it could still flake of and take the top coat with it. That's going to be a lot of work. Personally, I would start with the cheapest option and go from there. But whatever you choose get the wash off first so the new coating will penetrate the bricks.

[Guest JBaymore]

The rigidizer is likely a bad idea. Short term fix for long term loss. Will eventually deteriorate the bricks worse than they will already will go with the wood/soda.

 

Likely the soda was the main culprit in killing the hot face of the insulating firebricks. It will cause the hot face if the bricks to flux and therby shrink more than the rest of the brick which then will cause cracks paralell to the hot face which causes the bricks to spall (flake off). Then the prior owner probably used a basic kiln wash of some sort to try to help the situation....... which just added some mass (weight) to the inside face of the already spalling bits of brick.... causing them to fall off efven worse.

 

ITC 100 HT is really meant for application to NEW and clean and stable refractories. I've never had decent luck using it on old stuff that is already deteriorating. If you do try this...... use this stuff THIN! It does improve the emissivity of the kiln lining...... which evens out the firings and cuts fuel consumption. It MIGHT stabilize the bricks if you clean them well to start with (see below).

 

While it will seem like doing a lot of damage.... scrape off all the crap that the prior owner had applied first. (If BIG chunks of bricks start coming out as you do this .... you likely have the reason that the kiln was a "gift" to start with.) The kiln will look like hell then. Then use a stiff brush to dust off the surface completely. (Wear a GOOD well fitting respirator for ALL of this work.) Then wash the soft brick off with a re ally good dose of water.

 

Then the colloidal silica/zircon application is the way to go here. No, is is NOT sodium silicate.....water glass. DON'T use that!!!!!

 

best,

 

....................john

[DAY]

Remember- this is a FREE kiln!

[neilestrick]

Remember- this is a FREE kiln!

 

 

There is no such thing as a free kiln.

[Mark C.]

The rigidizer is likely a bad idea. Short term fix for long term loss. Will eventually deteriorate the bricks worse than they will already will go with the wood/soda.

 

Likely the soda was the main culprit in killing the hot face of the insulating firebricks. It will cause the hot face if the bricks to flux and therby shrink more than the rest of the brick which then will cause cracks paralell to the hot face which causes the bricks to spall (flake off). Then the prior owner probably used a basic kiln wash of some sort to try to help the situation....... which just added some mass (weight) to the inside face of the already spalling bits of brick.... causing them to fall off efven worse.

 

ITC 100 HT is really meant for application to NEW and clean and stable refractories. I've never had decent luck using it on old stuff that is already deteriorating. If you do try this...... use this stuff THIN! It does improve the emissivity of the kiln lining...... which evens out the firings and cuts fuel consumption. It MIGHT stabilize the bricks if you clean them well to start with (see below).

 

While it will seem like doing a lot of damage.... scrape off all the crap that the prior owner had applied first. (If BIG chunks of bricks start coming out as you do this .... you likely have the reason that the kiln was a "gift" to start with.) The kiln will look like hell then. Then use a stiff brush to dust off the surface completely. (Wear a GOOD well fitting respirator for ALL of this work.) Then wash the soft brick off with a re ally good dose of water.

 

Then the colloidal silica/zircon application is the way to go here. No, is is NOT sodium silicate.....water glass. DON'T use that!!!!!

 

best,

 

....................john

 

 

I think Johns idea getting down to new brick is right on track then coat it with my mixture I posted.

-Laguna clay Co sells the milled Zircon and you will have to source out a supplier that sells the colloidal silica by the gallon.

Mark

[Mark C.]

Here is a source for colloidal silica-Its sold in 1 gallon and 5 gallons.Mark

REMET Corporation

301 Turner Street

Utica NY 13502

Contact: Ed or John

Phone: 315-797-1845

Scott Martin - Inside Sales

REMET Corporation

Phone: (800) 445-2424 ext 277

Fax: (315) 797-4848

smartin@remet.com

[StefanAndersson]

Here is a source for colloidal silica-Its sold in 1 gallon and 5 gallons.Mark

REMET Corporation

301 Turner Street

Utica NY 13502

Contact: Ed or John

Phone: 315-797-1845

Scott Martin - Inside Sales

REMET Corporation

Phone: (800) 445-2424 ext 277

Fax: (315) 797-4848

smartin@remet.com

 

 

Thank you for this Mark. I will try your recepie.

[LilyT]

I wonder if Original Poster could upload a picture of the kiln? From her description

it doesn't sound like soda/atmospheric effects are fluxing the brickfaces. Could

the friable soft brick be due to the bricks having been exposed to moisture

and freeze damage? I have fired soda/wood ash in old soft brick kilns (hey, it's

what most of us can afford, right?) and it seems the exposed surfaces are

what get damaged, as a previous poster has suggested.

 

I have lined old electric kilns with a cheap brick repair mix of 50:50 Lincoln fireclay

and sawdust to help it insulate better, (I packed it into the grooves and molded

it over the face so the entire surface is covered). The fireclay is nice because

it has zero shrinkage when fired up to cone 10 - however note that there is

transient shrinkage at lower temps so if you use it initially at a ^5 or ^6 firing, it may

not work as well. This material was used in a conversion kiln that I subsequently

propane/wood/soda fired to cone 10. I've noticed it didn't all stay on 100% probably due

to my impatient packing - I had one 1-foot by 1-inch strip partially peel out of

the wall, though it didn't go far and didn't fall off. I feel that this can be used as

a layer of cheap protection for the brick.

 

If there is enough texture or grooves in face of the brick to make this mix stick,

it may be enough to lessen the crumbs and dust during the firing. You might use

a spray bottle to dampen the face of the brick while applying the coating to

help it cling better during the application.

 

Another thought is that kiln wash on the walls isn't always stable. I have made that

mistake, lol, hoping it would soak up some soda/ash to protect the brick. (alumina

hydrate 50, calcined EPK 50) In that case, in addition to tight packing, I took a

strong shop vac (outside and with a good quality dust mask) to blow and suck off

the unstable stuff before each firing. You have to run the open hose tip very close

to the wall to get good but not too aggressive cleaning. Like 1/4 inch. It's not perfect again,

but it lessens the floating junk, and I've had subsequent firings come out clean.

Oh, and be sure you remove any kiln wash from the ceiling of the kiln! Ask

me how I know:-). If you feel the need to cover the walls and ceiling, probably

the colloidal silica mix mentioned about would be more stable to vitrifying effects.

 

I hope some of my experience gives you ideas to help with your situation. These

old kilns require a bit of adjusting with each firing, kind of fun, but always

something to do and it adds terroir (if not terror) to your process... Good luck

and please post your results on what you did and what resulted!

 

Warmest regards,

-LilyT

[Mark C.]

I would be very careful applying anything to a lid or kiln roof-The kiln wash seems to be not the thing to use on inner walls. The alumina does not stick well and is always powdery-The colloidal silica (liquid) and milled Zircon sticks very well and does not come off easy unless you build up to much thickness.

LilyT-sounds like you have coated your fair share of old kilns

Mark

[LilyT]

Mark C, Your suggestion of avoiding coating the lid/roof is probably most wise.

I am eager to try your colloidal silica / zircon coating idea... I came across it

a few days ago in an independent search on a different topic. It sounds *great*,

thanks also for sharing the detailed instructions.

 

Would you also be so kind to share your technique for sandblasting? I have

not done that before as I tend to go low tech and manual first. I am

wanting to try it and am curious what machine / tool etc you use and

how to control it? Any tips and suggestions would be appreciated!

 

What an interesting conversation this is :-)

 

-LilyT

 

P.S., sorry to slightly hijack the topic...

[Mark C.]

You can pick up a cheap sandblaster at Harbor freight.com and get the sand from a lumber store- you need an air compressor as well to use one-you could rent one or borrow one.

The gun blasts sand which you will have to vacuum up later and can be reused if screened.You need eye and head protection as its messy-One could also use a small 4 inch grinder with safety guard removed-Do so at own risk-You did not hear that from me.

Mark

[LilyT]

You can pick up a cheap sandblaster at Harbor freight.com and get the sand from a lumber store- you need an air compressor as well to use one-you could rent one or borrow one.

The gun blasts sand which you will have to vacuum up later and can be reused if screened.You need eye and head protection as its messy-One could also use a small 4 inch grinder with safety guard removed-Do so at own risk-You did not hear that from me.

Mark

 

 

 

Aha, I love harbor freight... I will check it out. I am geeky and

like gadgets, I just don't use them as often as I should.

 

But ooh, I already have the 4 inch grinder with safety guard removed

(we didn't hear that from me, either) which we use to clean up the bad parts

on hardbrick after wood firing. What a good idea to use it on soft

brick, too. Your ideas are so innovative... brilliant! Do you think that

the sandblaster is more stable and the grinder sometimes takes out big

chunks by accident?

 

Lily

 

BTW I've been reading your post about spoon rest production.

Love it. All the details about making production and sales go fast

and efficiently are wonderful.