Suzanne Storer on mon 2 mar 98
I see in my supplier catalogue that vermiculite can be added to plaster to
lighten the weight of a plaster mold. Should it be added right after mixing
up the plaster and water? Makes sense to me to cover the object to be cast
with maybe a 3/8" coating of straight plaster before pouring on the
vermiculite/plaster mix. Anyone done this before? any tips?
Thanks, Suzanne
Jonathan Kaplan on mon 2 mar 98
>----------------------------Original message----------------------------
>I see in my supplier catalogue that vermiculite can be added to plaster to
>lighten the weight of a plaster mold. Should it be added right after mixing
>up the plaster and water? Makes sense to me to cover the object to be cast
>with maybe a 3/8" coating of straight plaster before pouring on the
>vermiculite/plaster mix. Anyone done this before? any tips?
>Thanks, Suzanne
I would descourage this practice as the vermiculite can migrate to the
casting surface or to whatever surface you are using and otherwise defeat
the ability of paster to pick up detail. Careful design of molds can yield
molds of appropriate weight.
While you could pre pour a skim coating, andthen perhaps use the method you
have outlined above, I would prefer to have my casting molds cast in a
single pour as the interface between two layeer of poaster will have way
different absorbancy characteristics than that of a single correct pour.
Jonathan
Jonathan Kaplan, president jonathan@csn.net
http://www.sni.net/ceramicdesign/
Ceramic Design Group Ltd./Production Services
PO Box 775112
Steamboat Springs CO 80477
(USPS deliveries only)
Plant Location
1280 13th Street Unit 13
Steamboat Springs CO 80487
( UPS, courier, and common carrier deliveries)
(970) 879-9139*voice and fax
http://www.sni.net/ceramicdesign/
http://digitalfire.com/education/clay/kaplan1.htm
KLeSueur on tue 3 mar 98
As an alterntive to plaster molds, you might try blue styrofoam from Dow. It
comes in many thickness. I cut it with a band saw and sand the edges. The
foam is far easier to fabricate than wood and it's open structure aids in even
drying.
All of my forms are drape. In other words, I lay the clay slab over the form
not in it. I've used this techique with foam as thick as three inches. If you
have trouble with release just dust the slab with cornstarch before draping.
Using foam has allowed me to have a consistance and finished pieces. In fact,
I'm often accused of ram pressing my slab work because of the consistancy.
Most of my forms are made by joining two pieces of foam. The top one is the
interior or bowl of the piece. The bottom one is wider and defines the rim. I
join them with wood glue.
I hate having plaster in my studio and this has allowed me to eliminate it.
Kathi LeSueur
Linda Blossom on tue 3 mar 98
When I tried adding vermiculite to plaster to make a mold, the vermiculite
floated. What a mess.
Linda Blossom
2366 Slaterville Rd.
Ithaca, NY 14850
6075397912
www.artscape.com
blossom@lightlink.com
-----Original Message-----
From: Suzanne Storer
To: Multiple recipients of list CLAYART
Date: Monday, March 02, 1998 11:08 AM
Subject: lightweight plaster molds
----------------------------Original message----------------------------
I see in my supplier catalogue that vermiculite can be added to plaster to
lighten the weight of a plaster mold. Should it be added right after mixing
up the plaster and water? Makes sense to me to cover the object to be cast
with maybe a 3/8" coating of straight plaster before pouring on the
vermiculite/plaster mix. Anyone done this before? any tips?
Thanks, Suzanne
MLCeramics on wed 4 mar 98
----------------------------Original message----------------------------
Most of my forms are made by joining two pieces of foam. The top one is the
interior or bowl of the piece. The bottom one is wider and defines the rim. I
join them with wood glue.
Kathi- Can you please elaborate on how you work with the foam. I am
particularly interested in this section about the two pieces which are joined.
Thanks, Meg Levine
mlceramics@aol.com
Darrol Shillingburg on wed 4 mar 98
Hi Suzanne and All,
You can make very large, thin and strong plaster molds by imbedding burlap
in the plaster. An open weave fabric is best, but most any will do. Put
down a "splash coat" of plaster and then lay down smallish pieces of burlap
that have been dipped in plaster. Covering the splash coat with burlap
before it sets will eliminate the tendency of the burlap to separate from
it. Overlapping the pieces of burlap builds
strength in the mold. Reinforce large flat section with strips of wood, or
pipe, or conduit attached with plaster and burlap. I've made many, many
molds this way, some as large 9'x9'. You can also use chopped fibers and
vermiculite in plaster, but I prefer burlap!
Darrol in Elephant Butte, NM
DarrolS@Zianet.com
on the web at http://www.zianet.com/DarrolS
>
> ----------------------------Original message----------------------------
> I see in my supplier catalogue that vermiculite can be added to plaster
to
> lighten the weight of a plaster mold. Should it be added right after
mixing
> up the plaster and water? Makes sense to me to cover the object to be
cast
> with maybe a 3/8" coating of straight plaster before pouring on the
> vermiculite/plaster mix. Anyone done this before? any tips?
> Thanks, Suzanne
John H. Rodgers on wed 4 mar 98
-- [ From: John H. Rodgers * EMC.Ver #2.5.02 ] --
Linda, I have used vermiculite lot. You have to wait until the plaster
begins to go toward a plastic state before adding the vermiculite or it will
float. There is a very narrow window of time that you will have in which to
mix it before it becomes to pastey to pour. Then you would have to spread it
on. Of course if you are going to use this mix to make a light weight mold,
a good splash coat would have to be applied to the model first, to get the
detail. the vermiculite will interfere. And you do run the risk of having
hard spots in the finished mold where absorption might be affected. For
carving and sculpture, though, the vermiculite/plaster makes a good working
material.
John Rodgers
In Alabama
-------- REPLY, Original message follows --------
Date: Tuesday, 03-Mar-98 01:03 PM
From: Linda Blossom \ Internet: (blossom@lightlink.com)
To: Clayart \ Internet: (clayart@lsv.uky.edu)
Subject: Re: lightweight plaster molds
----------------------------Original message----------------------------
When I tried adding vermiculite to plaster to make a mold, the vermiculite
floated. What a mess.
Linda Blossom
2366 Slaterville Rd.
Ithaca, NY 14850
6075397912
www.artscape.com
blossom@lightlink.com
-----Original Message-----
From: Suzanne Storer
To: Multiple recipients of list CLAYART
Date: Monday, March 02, 1998 11:08 AM
Subject: lightweight plaster molds
----------------------------Original message----------------------------
I see in my supplier catalogue that vermiculite can be added to plaster to
lighten the weight of a plaster mold. Should it be added right after mixing
up the plaster and water? Makes sense to me to cover the object to be cast
with maybe a 3/8" coating of straight plaster before pouring on the
vermiculite/plaster mix. Anyone done this before? any tips? Thanks,
Suzanne
-------- REPLY, End of original message --------
KLeSueur on thu 5 mar 98
In a message dated 3/4/98 8:56:16 AM, you wrote:
<interior or bowl of the piece. The bottom one is wider and defines the rim. I
join them with wood glue.
Kathi- Can you please elaborate on how you work with the foam. I am
particularly interested in this section about the two pieces which are joined.
Thanks, Meg Levine>>
Example: square bowl form, 2" deep with a 1/2" rim.
I would first decide the top and bottom dimensions of the bowl form. In this
case, 12" wide at the rim of the bowl and 8" in the bottom. I would draw the
outline of the top of the bowl form on a piece of 2" styrofoam and then
calculate the angle I would need to cut to get an 8" bottom. I would then set
my bandsaw ( just a small Delta model, but you could use a jig saw) to the
proper angle and cut out the form.
For the rim, I would take a piece of 1/2" styrofoam and draw the same shape as
the top of the bowl, but 1" wider all around. Then cut out this piece.
I would sand the edges of the bowl form that make the bottom so that the form
is slightly rounded.
To join the pieces, I use Elmer's wood glue applied to both surfaces. Then
center the bowl form on the rim form and let dry.
The slabs I use are just slightly over 1/4". I carefully drape them and use a
sponge to coax the clay around the form. Use a metal scraper ( a wall paper
scraper works well) to smooth the bottom. I cut off excess clay with a pin
tool. It's less likely to damage the form than a fettling knife. Let dry until
the edges are just lifting off of the form. (If your studio is drafty turn the
forms. If one side starts to dry too rapidly just dampen it with a sponge)
Then flip over and they should release.
I use a cheese cutter to put a bevel on the edge and smooth with a sponge. I
dry everything face down on styroform sheets until at least leather hard.
Good luck,
Kathi LeSueur
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