Page 1 of 1

bentonite for sand casting

Posted: Mon Jan 19, 2004 10:51 pm
by Bert Weiss
I have read here that bentonite can be mixed with sand as an alternative to dry plaster. I have had great results using olivine sand and plaster.

i was speaking with a foundry guy today who told me that he thought that an olivine/bentonite mix would need 5% water to work right. he thought that the water was needed to disperse the bentonite around the sand.

I don't picture that the moist pac would be good to use for kiln fired glass.

Can anybody tell me about how they use the bentonite for kiln casting. Is it good as a seperator dusting?

Posted: Mon Jan 19, 2004 10:56 pm
by Brock
That Olivine/Bentonite/water mix is what is used for sand casting with molten glass. Haven't used it in a kiln. Brock

Posted: Tue Jan 20, 2004 7:57 am
by rosanna gusler
aussie john was the one that said he used it. he said dry. it is a fine powder. i have 25lbs of it sitting on the floor waiting for my spare time to show up. rosanna

Posted: Tue Jan 20, 2004 12:43 pm
by rgm
Bert
I did a casting workshop with Berteil V. some years ago and have his sand mixture on paper - will post if you need it but he adds only 5
percent bentonite well mixed into the sand .
Robert

Posted: Tue Jan 20, 2004 1:26 pm
by rodney
Robert Middlestead wrote:Bert
I did a casting workshop with Berteil V. some years ago and have his sand mixture on paper - will post if you need it but he adds only 5
percent bentonite well mixed into the sand .
Robert
,,,,,,,,,,,,,,thanks robert, would you kindly send the info on what berteil v. does with this

is the water in the mix for the molten glass used to prevent the side wall of the sand from caving in,,,,,,if a persons uses a sheet of glass, what keeps the tops of any peaks from becoming flat

once the process is complete, is there ever any need for cold working, is there any sticking

thanks
rodney

Posted: Tue Jan 20, 2004 5:53 pm
by Bert Weiss
Robert Middlestead wrote:Bert
I did a casting workshop with Berteil V. some years ago and have his sand mixture on paper - will post if you need it but he adds only 5
percent bentonite well mixed into the sand .
Robert
I too took sand casting with Bertil V. and Paul M. Kiln casting is a different animal.

Posted: Tue Jan 20, 2004 9:17 pm
by rgm
So it is - guess I have to read every word more carefully .

Posted: Wed Jan 21, 2004 11:48 am
by charlie holden
Robert Middlestead wrote:Bert
I did a casting workshop with Berteil V. some years ago and have his sand mixture on paper - will post if you need it but he adds only 5
percent bentonite well mixed into the sand .
Robert
Robert,

I'm interested in what Berteil uses for the negative forms in his pieces. This is for hot casting. He pre-forms some sand mixture, often into heads and faces, and places them into the bottom of molds to make a negative space. Do you know what he uses for this?

We tried using sodium silicate bonded sand last summer at Pilchuck but it turned into hard rock during annealing. The word was that his negative forms turn to powder during annealing. I've heard he may use some kind of oil bonded sand from the UK. Are you familiar with this?

Thanks, ch

Posted: Wed Jan 21, 2004 5:52 pm
by Bert Weiss
Charlie

We used 2 meshes of olivine sand and bentonite. I don't remember the percentages, but I probably have the notes at home (where I'm not).

First you sift the sand in to a box so that it is lofty. Then he presses in his large form, like the boat hull. Then he presses in objects. You could use anything from plastic toys to wooden carvings... Finally the mold is coated with graphite or carbon from an acetylene torch in places where he doesn't want the sand to stick. No carbon where he wants it to stick. Then molten glass is poured in, using a team of ladlers. As the mold fills up, he drops in objects made of compatible glass or copper foil. The whole box,sand and glass goes in to the annealer...

Posted: Thu Jan 22, 2004 1:29 am
by rgm
Berteils small negative pieces ie little figures do turn to powder after the
process but we didn`t make any during the class . He said someone
makes them for him in Sweden . Berteil has the luxury of working for
a large glass production co. so has many helpers . Someone emailed
me for his sand mix . He gave us two versions :
1/4 old sand
1/4 60 mesh
1/2 90 mesh
5 percent bentonite

Second version :
equal parts - 80 mesh and 120 mesh sand with 5 percent bentonite
A lot of time is spent mixing this stuff . He emphasized that .

Posted: Thu Jan 22, 2004 4:30 am
by Kevin Midgley
Get an odd-job (that isd what it is called) Canadian made cement mixer for mixing mold materials. It is a small plastic barrel with baffles inside that is designed for a full bag of redimix cement. You dump in your materials lock on the lid and roll it across the floor. Works fast. They are under $40 Cdn. Kevin in Tofino

Posted: Tue Jan 27, 2004 1:25 am
by rgm
Does anyone have Warren Langley`s exact sand mixture for kiln
casting ?

Posted: Tue Jan 27, 2004 3:39 pm
by Bill Grix
Hi Robert
I was in Warrens class last summer. his sand, plaster mix was 80% sand to 20%plaster.

Bill

Posted: Wed Jan 28, 2004 12:09 pm
by rgm
Thanks Bill - was that olivine sand ?

Posted: Wed Jan 28, 2004 2:18 pm
by Lionel
80-10-10 sand/bent/water but you need to mull the hell out of it - I use my truck to run it over a few times. You also should use a steel frame and pack it with a ram. The mold has to be heated to 200 for about 8 hours to get all the water out before you charge or you will have big bubbles in your glass. Lots of torching helps for release.


http://home2.nikonnet.com/servlet/com.a ... emberguest

Posted: Wed Jan 28, 2004 3:46 pm
by Bill Grix
Hi Robert
Warren said he uses any kind of sand, he like the differnt texures you can get. I use silica and get good results. No need for bentonite or mulling.

Bill