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duraboard as dams

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Carol
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duraboard as dams

Postby Carol » Tue Apr 13, 2004 11:14 am

Am considering using duraboard strips as dams since I can get longer lengths than with cut-up mullite shelves. I know it's an insulator while mullite transmits heat.

Do I need to modify my firing schedule to compensate for the insulating nature of the duraboard? Can I mix duraboard and mullite dams in the same kiln load? Can I mix them on the same piece? Any other pros/cons to using duraboard dams?

Thanks

Carol

Phil Hoppes
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Postby Phil Hoppes » Tue Apr 13, 2004 11:40 am

Should not be a problem. I would not think that you would need to modify your schedule. You would want to rigidize them again after they are cut so that all faces have been rigidized. Also you obviously need to kilnwash them too. I'd probably use fiberpaper as a buffer between them and the glass just to be on the safe side. I've used fiberboard as a dam for thick oval shapes I've been firing (sinks). It works fine. As a stand alone dam the only caution is to not cut them too narrow or if they are narrow you may want to put some bricks, kiln furniture, etc. something heavy behind so if you are fusing something very thick (> 1/2") the weight of the glass does not move the dam. This shouldn't really happen but I always error on the side of caution. An ounce of prevention is always better than a pound of cure.

On the schedule, if you are really concerned, do a test case to see what it does. I always do this when I'm reaching in unknown territory.

Phil

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Postby Brad Walker » Tue Apr 13, 2004 11:43 am

I have used Duraboard, mullite, Ceramaguard, and Skamol board as dam material. In each case I have lined the material with strips of 1/4" thick fiber paper. My experience has been that the differences between the products is minimal, and I have seen no issues from mixing the different types in one firing.

On a similar subject, I have butted the material together end to end when I needed a longer piece than I had in hand. Once this is lined with a long strip of fiber paper (easily available from the roll, as long as needed), it works just as well as a single long piece of dam material. In fact, given that longer pieces sometimes warp, I prefer using shorter pieces end to end. I've done this for dams up to 3 feet long, but don't know why it wouldn't work for even longer ones.

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Postby Bert Weiss » Tue Apr 13, 2004 2:24 pm

Phil Hoppes wrote:Should not be a problem. I would not think that you would need to modify your schedule. You would want to rigidize them again after they are cut so that all faces have been rigidized. Also you obviously need to kilnwash them too. I'd probably use fiberpaper as a buffer between them and the glass just to be on the safe side. I've used fiberboard as a dam for thick oval shapes I've been firing (sinks). It works fine. As a stand alone dam the only caution is to not cut them too narrow or if they are narrow you may want to put some bricks, kiln furniture, etc. something heavy behind so if you are fusing something very thick (> 1/2") the weight of the glass does not move the dam. This shouldn't really happen but I always error on the side of caution. An ounce of prevention is always better than a pound of cure.

On the schedule, if you are really concerned, do a test case to see what it does. I always do this when I'm reaching in unknown territory.

Phil


Phil

I don't understand the desire to rigidize board. They come rigidized when you buy them. Why bother? I never have and I don't see why I would want to.
Bert

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Postby Phil Hoppes » Tue Apr 13, 2004 4:15 pm

Bert Weiss wrote:
Phil Hoppes wrote:Should not be a problem. I would not think that you would need to modify your schedule. You would want to rigidize them again after they are cut so that all faces have been rigidized. Also you obviously need to kilnwash them too. I'd probably use fiberpaper as a buffer between them and the glass just to be on the safe side. I've used fiberboard as a dam for thick oval shapes I've been firing (sinks). It works fine. As a stand alone dam the only caution is to not cut them too narrow or if they are narrow you may want to put some bricks, kiln furniture, etc. something heavy behind so if you are fusing something very thick (> 1/2") the weight of the glass does not move the dam. This shouldn't really happen but I always error on the side of caution. An ounce of prevention is always better than a pound of cure.

On the schedule, if you are really concerned, do a test case to see what it does. I always do this when I'm reaching in unknown territory.

Phil


Phil

I don't understand the desire to rigidize board. They come rigidized when you buy them. Why bother? I never have and I don't see why I would want to.


Bert,

Not where I buy them, unless I'm confusing a brand name with something else. All my shelves are Low Density Duraboard manufactured by Unifrax. I get mine directly from Unifrax. They are not rigidized. Never bought them any other place but I would not imagine that they are rigidized there either. Plus, even if they are rigidized on the surface, as soon as you cut one up the interior sides you cut with a knife are now untreated board for at least that portion where the original rigidizer did not soak in. I guess you don't have to treat them but the fiber particulate that comes with working with them is not that good for you. Rigidizing keeps that down as well as making a harder surface.

Phil

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Postby Bert Weiss » Tue Apr 13, 2004 5:31 pm

Phil Hoppes wrote:Bert,

Not where I buy them, unless I'm confusing a brand name with something else. All my shelves are Low Density Duraboard manufactured by Unifrax. I get mine directly from Unifrax. They are not rigidized. Never bought them any other place but I would not imagine that they are rigidized there either. Plus, even if they are rigidized on the surface, as soon as you cut one up the interior sides you cut with a knife are now untreated board for at least that portion where the original rigidizer did not soak in. I guess you don't have to treat them but the fiber particulate that comes with working with them is not that good for you. Rigidizing keeps that down as well as making a harder surface.

Phil


I do use HD board sometimes. The HD stands for high density and it somewhat more rigid than LD. I have worked with LD board and not rigidized and it does stick a bit so I can see the efficacy of using the colloidal alumina.

Using colloidal silica simply adds more toxic particles to the mix. If I understand correctly, cristabolite is created when colloidal silica is heated and cristabolite is a much more dangerous particle than alumina silicate fiber. On the other hand colloidal alumina will make the board more rigid, and less sticky, which are both good properties.
Bert



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Carol
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Postby Carol » Tue Apr 13, 2004 6:38 pm

Bert Weiss wrote:[
I do use HD board sometimes. The HD stands for high density and it somewhat more rigid than LD. I have worked with LD board and not rigidized and it does stick a bit so I can see the efficacy of using the colloidal alumina.

Using colloidal silica simply adds more toxic particles to the mix. If I understand correctly, cristabolite is created when colloidal silica is heated and cristabolite is a much more dangerous particle than alumina silicate fiber. On the other hand colloidal alumina will make the board more rigid, and less sticky, which are both good properties.


So if I understand you, the HD board doesn't need a rigidizer for strength, but to prevent sticking? Would a sifted layer of plaster or kiln wash do the same thing?

Carol

Phil Hoppes
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Postby Phil Hoppes » Tue Apr 13, 2004 6:51 pm

Looking at the Unifrax web site, neither HD or LD board is rigidized as sold by Unifrax. The colloidal alumina Bert speaks of is a better way to go than colloidal silica. You can choose to rigidize or not, it's up to you. According to the Unifrax info sheets, HD boards are LD boards with the addition of clay. You can purchase RG boards from Unifrax which are already rigidized. HD boards are made mostly for applications where higher weights are to be supported as they have a higher modulus of rupture (MOR) than the LD boards. If you go to the Unifrax website:

http://www.unifrax.com

and click on products and then click on boards and then click on Duraboard you will see all of the Duraboard products they manufacture. You can click on each datasheet as well as MSDS (Material Safety Data Sheet). If you read these through, neither of these are great for you. By cutting one you expose an edge that is non rigidized (I'm guessing even if you have the RG boards). To keep particulate matter down I would recommend rigidizing them. If you can get colloidal alumina as Bert recommends, it is the best solution.

Phil

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Postby charlie » Tue Apr 13, 2004 6:56 pm

Carol wrote:So if I understand you, the HD board doesn't need a rigidizer for strength, but to prevent sticking? Would a sifted layer of plaster or kiln wash do the same thing?

Carol


it's tough to sift it on a vertical face of a dam and get it to stick :)

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Postby Carol » Tue Apr 13, 2004 7:09 pm

charlie wrote:
it's tough to sift it on a vertical face of a dam and get it to stick :)


Very true, LOL. I use fiber paper inside my dams as it has a bit of "give" which I figure is a good thing as the glass expands.

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Postby Bert Weiss » Tue Apr 13, 2004 10:25 pm

Phil

The process of making a board is to take fiber and rigidizer of some sort and form a board. Blanket is not rigidized. Boards are. The LD boards have less mass then the HD boards. The mass is rigidizing material that is soaked in to the fibers. You can of course continue to rigidize the boards on your own.

You could kiln wash the board rigidized or not. Paper is a good interface. Carol has HD boards on hand and I don't see a neccessity to further rigidize it after cutting, although I won't argue that it won't help seal in the fibers.
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Phil Hoppes
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Postby Phil Hoppes » Wed Apr 14, 2004 12:44 am

Bert,

I coat my LD boards with NALCO which as I understand it is basically colloidal silica. When these boards arrive from Unifrax, they are soft, flaky and can easily break and chip. I coat them with NALCO and burn them out. The surface becomes like ceramic. If you flick it with your finger it sounds like china. You can then sand the surface to make it smooth. I coat them with a solution of kilnwash and more NALCO and fire them high again. This makes a very hard surface that I again sand smooth. By this time most if not all surface defects are gone. I typically wash them again and fire again. By this time they are ready for glass. After they've been fired and washed about a half dozen times I can usually get two or three firings between having to wash them.

I'll be the first to admidt I'm not a chemist. If the binders Unifrax talks about in their product breif is what you are calling rigidizer, then they come rigidized. For me, when they come from the factory they blow dust all over the place. There is a SIGNIFICANT difference in the surface and handling properties of these boards after I've rigidized them with colloidal silica. From the factory, I can't handle them without wearing a respirator as they make me hack all over the place. I soak them and cook them up with the NALCO and they work great. No dust. No chipping. No flaking.
I get NALCO from Western Industrial Ceramics. It comes in liquid form and runs about $1.00/lb. This is something I learned from Doug Randall as this is how he preps his boards.

When I've ordered NALCO from Western, once they asked if I wanted rigidizer or colloidal silica. I asked what was the difference. I was told that rigidizer was about 4x more than the colloidal silica I was buying. I remember what Doug said he paid for Colloidal silica so I figured NALCO was what he got. I just Google'd NALCO and didn't come up with much other than there is a chemical company that works with refractories called NALCO. They got the original patent on colloidal silica in 1957 so I'm guessing that what I have is colloidal silica. Judging by what you've found out in your other post, looks like colloidal alumina is a better way to go and will probably be what I use in the future. Either way, for me, I don't care to use the Unifrax Duraborad as it is from the factory. At least the LD boards. I've no need for HD boards as they cost more and weigh a lot more and the enitre reason I've gone away from mullite is because they are so d*#&* heavy and I'm convinced they can't be made large and flat. (At least I haven't found any).

BTW, the difference between HD and LD boards is that there is clay in the HD boards. Don't take my word for it, this is directly from the Unifrax product brief's on thier web site.

Phil

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Postby Amy Schleif-Mohr » Wed Apr 14, 2004 8:55 am

Hi Carol,

I just read this thread for the first time. I just wanted to chime in and recommend a cutting tool, if you haven't cut your board yet. I cut board all the time and what I've found to work the best/quickest is a drywall saw. It's only a couple of bucks at the hardware store and you have lots of control. I've tried utility blades and a few other things. The drywall saw works the best by far.

I would also recommend that you back up all your dams with bricks. I just use regular bricks that I have burned out.

Just one more thing. If you have board dams (long ones, like 20" or more) and a board shelf, be careful. The shelf will eventually warp and if you put a nice streight dam on it there will be a gap and the glass will run out. This has been my experience. So, don't discount the shorter mullite dams end to end. And kiln wash the whole dam, sometimes the paper can fail or the glass will leak. This makes more work later.

Amy

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Postby Gail Bunt » Thu Apr 15, 2004 7:49 pm

I'm a newbie, just tried to make my first mold out of fiber blanket rigidized with colloidal silica hardener/rigidizer. Put it on my only full kiln shelf and YECHHH, what a mess.

Colloidal silica dries at a glacial pace. I tried drying it in the kiln at 160F (the instructions threaten to set the kiln on fire over 175). It was nowhere near dry after several hours. Took it off the shelf to dry in the room; days later it is no drier, though humidity here is low.

I needed the shelf so eventually dried the shelf in the kiln at 500F. The stench of the colloidal silica burning off was enough to gag a goat, despite venting both the kiln and the room. The shelf no longer soaks up kiln wash the way it used to. I am firing on it now and crossing my fingers that the piece doesn't stick.

I'd like to try hardening some Durabord, but no way am I using any more colloidal silica. Who sells colloidal alumina? Don't suppose there a source in Canada?

Gail

Phil Hoppes
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Postby Phil Hoppes » Thu Apr 15, 2004 8:18 pm

Bert had a previous post on this. He will probably pipe in but if not, check the archives for Bert Weiss and collodial alumina. You get it in a powderd form. It is safer than colloidal silica and dries harder as I understand it.

On the colloidal silica, I put it on and ramp my kiln at 500DPH to 500 and hold it for 2 - 3 hours and then shoot up to 1600 to burn it out. Up to the 500 and at the 500 my kiln is well vented. Never had a problem doing it this way. It steams like crazy for the first hour.

On the stink, Duraborad is going to stink even if you don't treat it as you are burning out the binders in the board.

Phil

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Postby Gail Bunt » Thu Apr 15, 2004 8:34 pm

Phil,

Thanks for the info. Once I got into bail-out mode with the colloidal silica, I didn't think to finish it off by going up to 1600. Glad to hear the smell was just the binders.

I found Bert's post re colloidal alumina and will contact them. It's http://www.wesbond.com/wesolok_db.htm.

Gail

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Postby Lynne Chappell » Mon Apr 19, 2004 12:02 am

I just want to clarify something for those who haven't used rigidizer yet. Regular duraboard doesn't stick to glass (well a few fibers come off with the glass, but brush off it). If you rigidize with the usual stuff (colloidal silica, and Hotline rigidizer and probably most others), then it will stick to your glass like crazy. You must use kiln wash then, and reapply even more stringently than you do with your kiln shelf. If your wash on your kiln shelf starts breaking down, you get some kiln wash stuck to the bottom of your glass. If the wash on your rigidized fiber breaks down, a whole chunk of the fiber will come off stuck to your glass. If you don't kiln wash it at all, I shudder to think of the mess.

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Postby Phil Hoppes » Mon Apr 19, 2004 10:58 am

OK, I got a question here. Bert and I were discussing things back and fourth and I really had a question but I did not explain myself well enough. Bert mentions that Duraboard comes from the factory rigidized. Other people mention rigidizer, colloidal silica, colloidal alumina, etc. Anyway, the word rigidizer seems to be used in a ubiquitous fashion but I don't think it is the same thing in all cases and maybe should not be used this way. So for clarification I have a few of my own dumb questions:

1) Does duraboard get hard on the surface (like china) when it is just burned out as it comes from the factory? (I have not done this as I was instructed to always put colloidal silica on first and then fire it up so I don't really know if it gets a hard surface)

2) Is colloidal silica rigidizer? (Not a dumb question I think as if you read the above thread, rigidizer from Western Industrial Ceramics was like 4x the cost of colloidal silica. If they are the same stuff, why the 4x difference in cost. If they are NOT the same stuff, then what the heck is rigidizer?)

3) Bert mentions the boards come from the factory rigidized. Ok, I'll buy that but again to question 2, what the heck is rigidizer. Is it the sugar based binders that are used to hold the board together when they press it? Unifrax's website discusses many of their products in a product brief. Here they mention an RG, LD, HD and numerous other versions. In reading this it is a little appearant that they mention at least the RG is rigidized. You can kind of imply from their description that the others are also rigidized. They mention the HD has clay put in. Again, is clay a rigidizer? I guess I wouldn't call it that, I'd call it clay.

I might suggest that if rigidizer is NOT specifically the chemical colloidal silica, but relates to a specific chemical then it should not be used as a general term or if it is used as a general term the user should then elaborate on what exact chemical or material is being referenced as I believe the term "rigidizer" is being confused for a lot of different things. Depending upon ones experience, background, etc. this word means a lot of different things to a lot of different people. For one, it would certainly help me that is for sure.

To answer your question Lynn, you get one honking mess when you don't kilnwash properly. When I first starting using duraboard shelves I washed them with colloidal silica, burned them out and then started using them like my mullite shelves. This happend when I had only used them a few times but after the 2nd or 3rd time I got lazy and didn't wash in between firings and figured I could cheat a little like I could with a mullite shelf. WRONG!!! I had an 8" plate I was firing. It pulled a hole out of the board 8" in diameter and about 1/4" deep. Now that I've been firing them a lot (20 times or so) I can cheat a little if I want as I've been building a nice layer of wash up on my shelves. I've just been rewashing them every time without cleaning them off. Actually this works very well to smooth them out. In doing this there is a thin but VERY smooth layer of wash that I now lightly sand with very fine sandpaper (using a respirator with duraborad and colloidal silica!). My boards now are very, very smooth. I get outstanding results with the back finish on my glass. It takes quite a few treatments but it's worth it once it is all done.

Phil
Last edited by Phil Hoppes on Mon Apr 19, 2004 1:35 pm, edited 1 time in total.

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Postby Bert Weiss » Mon Apr 19, 2004 1:07 pm

I'm not quite a scientist or engineer here just a seat of the pants guy. I guess there are different materials that result in making fibers more rigid. It seems like there is clay of some sort, colloidal silica, colloidal alumina and possibly some other additives.

I'll make a guess that possibly the more expensive rigidizer is less concentrated but the same stuff?

Typically silica is a material that sticks to glass. Alumina is a material that does not stick. This is why kiln wash is essentially alumina. Kaolin the other ingredient in kiln wash is a high alumina content clay.

I have found that all it takes to seperate my float glass if a VERY thin layer of kiln wash. A single pass with a highly diluted mixture on a mullite shelf. Others say that it takes a heavier concentration to keep BE from sticking.

From what I have been told an essential difference between colloidal alumina and colloidal silica is that the alumina sinks in more than the silica. The silica remains on the surface and results in that hard hollow sounding surface. Since I haven't used the alumina on Unifrax boards, I can't comment on how that works, but I am told that it will sink in more.

I am working in my head on a new kiln wash that is basically alumina and mica (optional) mixed with CMC (home made Klyr fire). This mixture would be sprayed on, and wiped off after firing, and reused. I have not tried it yet so I don't know why it hasn't been marketed. Possibly because you have to mix the liquid component and the solid at the time of use. It seems to me that the CMC will make a better binder than EPK as it does not do the scum thing and it burns out so would be reusable. Maybe I'm dreaming... I think the mica is a really cool material for use in a kiln wash. It doesn't stick to float and if it does stick to BE, it would leave an irridescent sheen. Two seperate issues here, CMC as a binder for reusable kiln wash and mica as a component in a kiln wash mix.
Bert



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Re: duraboard as dams

Postby Terry Gallentine » Wed Sep 13, 2017 11:53 am

I needed a large shelf for my new kiln so I rigidized a 42"x48"X1/2" piece of Duraboard ES with colloidal alumina (Wesolok D). I dried it thoroughly before firing it but the board still warped when I fired it. Does anyone have any ideas of how to take the Duraboard back to a flat state? Does wetting it, pressing it and drying it work after it has been fired once?


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