Randall Moody on thu 8 mar 07
I have a commission for a large window surround to be sculpted, cast and
then machined in stone with a multi-axis router. The piece will end up being
around 4' x 4' by 1' deep. Does anyone have experience casting something
this large in plaster? Is there any way to stabilize or strengthen the
plaster for shipping? I am thinking maybe some sort of cheesecloth/gauze
type of material in the plaster. Any pointers would be greatly appreciated!
Nervous Randall in Atlanta
stephani stephenson on thu 8 mar 07
you can use sisal .
Sisal, hemp , also goes by other names, is a
traditional additive for large molds.
the fibers are very long and can be used to reinforce
molds of great size.
i think the largest i have made is over 3 feet ,
you add the fibers after the face coat and first
layers of plaster have started to thicken fibers are
laid into the subsequent slurry of plaster.
check out Douglas and Sturgiss or the Compleat
Sculptor or other sources online for prices and
availability. sisal was used for packing and all kinds
of things years ago, was plentiful and cheap...is
still carried by scupture supply...
also i would use a gypsum cement rather than a pottery
plaster. something like hydrocal,etc. check into which
one will best suit your purposes...depending on the
other materials involved.
a stronger gypsum cement will allow you to make the
mold thinner as well.
you might also pour the mold into a sturdy frame of
wood to protect it during shipping and handling put
some dowels or something to protrude into the plaster
to hold it...haven't tried that... just an idea...
Stephani Stephenson
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John Jensen on thu 8 mar 07
Big project...lots to learn and know.
Two things I've used to reinforce plaster: Burlap and loose hemp
fiber. Some one gave me the fibre, so I don't know where to get it;
but it works marvelously and takes more or less any shape. Since it
is loose it works in three dimensions; unlike burlap, which is in
sheets.
John Jensen, Homewood Pottery
homewoodpottery.com
johnjensen@homewoodpottery.com
>=20
> I have a commission for a large window surround to be sculpted, cast
> and
> then machined in stone with a multi-axis router. The piece will end
> up being
> around 4' x 4' by 1' deep. Does anyone have experience casting
> something
> this large in plaster? Is there any way to stabilize or strengthen
> the
> plaster for shipping? I am thinking maybe some sort of
> cheesecloth/gauze
> type of material in the plaster. Any pointers would be greatly
> appreciated!
>=20
> Nervous Randall in Atlanta
Megan Mason on thu 8 mar 07
Dear Randall,
How about nylon fibers? The cement folks use them.I also have somei bought
from Dupont that are about 1/2 '' or longer, never measured them that I have
used.
Meg
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John Rodgers on thu 8 mar 07
I re-inforce plaster with loose hemp fiber that I get from
www.polytek.com. Get their catalog. It has a world of info in it about
how to work with molds, plasters, rubber compounds and re-inforcing
materials.
Regards,
John Rodgers
Chelsea, AL
Randall Moody wrote:
> I have a commission for a large window surround to be sculpted, cast and
> then machined in stone with a multi-axis router. The piece will end up
> being
> around 4' x 4' by 1' deep. Does anyone have experience casting something
> this large in plaster? Is there any way to stabilize or strengthen the
> plaster for shipping? I am thinking maybe some sort of cheesecloth/gauze
> type of material in the plaster. Any pointers would be greatly
> appreciated!
>
> Nervous Randall in Atlanta
>
> ______________________________________________________________________________
>
> Send postings to clayart@lsv.ceramics.org
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> melpots@pclink.com.
>
>
Lois Ruben Aronow on thu 8 mar 07
You can go on Uline and get expanding/form-fitting foam. I'm assuming you
already know you'll need to crate the piece.
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Randall Moody
Sent: Thursday, March 08, 2007 8:29 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Clay related, Plaster
I have a commission for a large window surround to be sculpted, cast and
then machined in stone with a multi-axis router. The piece will end up being
around 4' x 4' by 1' deep. Does anyone have experience casting something
this large in plaster? Is there any way to stabilize or strengthen the
plaster for shipping? I am thinking maybe some sort of cheesecloth/gauze
type of material in the plaster. Any pointers would be greatly appreciated!
Nervous Randall in Atlanta
____________________________________________________________________________
__
Send postings to clayart@lsv.ceramics.org
You may look at the archives for the list or change your subscription
settings from http://www.ceramics.org/clayart/
Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
stephani stephenson on thu 8 mar 07
one nice thing about the sisal/hemp fibers is that they are long,long,long
a couple of feet long ,sometimes more...
also they can be pulled apart and you can use as little or much as you want...
You don't need to use very much, so you are not adding much weight..you want to try to get every strand submerged and surrounded by the gypsum/plaster.....
but it isn't a fussy part of the process. the fibers are quite strong, thin as they are
i have attempted to break some old molds, and the fibers had not rotted and were in better shape than the well used mold,actually.
i tried adding perlite to a mold once..now that i think of it, it was over 4 feet long...a large banana tree leaf. i did the face coat with ceramical, then backed it up with 2-3 inches of B-11 into which i stirred perlite...( i have a lot of that on hand and i was trying to lower the weight of the mold and also save on quantity of gypsum cement used.
when i added the perlite to the B-ll it made the batch thicken. rapidly. i didn't think about adding more water to compensate for the perlite sucking the water out of the plaster mix!
i wasn't sure it was going off so i mixed and poured the gloppy stuff quickly. when it was still shy of going off completely i scraped the back surface to submerge/shave any perlite protrusions...
considering it was just a gamble and i did it on impulse, it actually worked pretty well...the mold, for as big as it is, is something i can lift by myself and it is quite strong and seems to handle pressing well.... about 3" thick
i know there are other additives to lighten the plaster as well...glass balloons i believe and also i know that , in cement anyway, even things like sawdust and packing peanuts ,etc are added to lighten backing layers.....
helps if you experiment on something small and not important first though!
Stephani Stephenson
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Randall Moody on fri 9 mar 07
Thanks to everyone for their help in this! I am now torn between sisal and
fiberglass gauze.I can see the benefits of both and will probably make up my
mind based on the ready availability and cost of each. Now the fun part
begins! I will post the results when I am finished.
Randall.
amamenec@lineone.net on fri 9 mar 07
Any kind of celulose fiber will make the plaster cast very heavy at=20
this scale. Not to mention likely to go mouldy too. And a little=20
brittle. I've recently made a lifesized 4 piece mould using loose=20
weave fiberglass matting, and a little loose polypropeline fibers for=20
good measure, all in a very hard plaster to make a 1" thick plaster=20
jacket which is fairly light given the size of the panels. The plaster=20
I used was Prestia Creation, very hard, but you could try something=20
that sets hard local to you I'm sure.=20
How I made this was to mix the first batch without any additions and=20
'threw' the mix at the piece to be cast. This gave a thin fine coat.=20
Secondly I mixed severaly batches of plaster, and with each batch I=20
tore hand-sized pieces of the loose weave fiberglass and battered them=20
as you woulld say batter a cod, and then slapped each plaster battered=20
patch onto the the object being cast, overlapping each piece as I went.=20
I carried on adding patches and mixing batches of plaster intill I'd=20
made a 1" to 1 1/2" depth. Then I tidied it up and cranked it open. I=20
was casting onto clay so separation of the object and the plaster was=20
not a problem. If I'm casting onto anything other than leatherhard clay=20
I paint on vaseline thinned with white spirit first.
Hope that's useful. Let us know how you've done it when you have! Best=20
wishes,
Ama Menec, Totnes, Devon, UK.
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