Ruth Ballou on sat 15 sep 07
Not a plaster queen, nor do I play one on TV but this method has =20
worked well for me.
Lose the pounds and ounces and try the metric system to figure out =20
this plaster stuff a lot faster. Most of the bother in mixing plaster
is related to converting US volume measurement to weight. The metric =20
system tidily eliminates this bother.
Only one calculation required. You can easily figure out the volume =20
of the item by filling it with water,
or by using displacement, if it is an object that can't be filled, =20
and then measure the water in a metric container,
i.e. in milliliters. Since one milliliter weighs one gram, this IS =20
the weight of the plaster in grams required for the object.
Multiply that number by the desired percentage of water, 75% being =20
what has typically been recommended
on clayart in the past. Measure out that with the same metric =20
container. Hamer and Hamer have a wonderful chart
for proportions of water to plaster, depending on the type of mold =20
being made.
Ruth Ballou
Surrounded by boxes in
Silver Spring, MD
On Sep 15, 2007, at 4:59 AM, Cindy reed wrote:
> I took a mold making class last spring and this is a water to =20
> plaster table
> we used at school:
>
> Water @ 72=B0F/22=B0C Plaster
>
> A. 236 ml (cc) 11 oz. 312 grams
> B. 473 ml (cc) 1 lb. 6 oz. 642 grams
> C. 946 ml (cc) 2 lb. 12 oz. 1.248 grams
> D. 1,419 ml (cc) 4 lb. 2 oz. 1,872 grams
> E. 1,892 ml (cc) 5 lb. 8 oz. 2,497 grams
> F. 2,365 ml (cc) 6 lb. 14 oz. 3,021 grams
> G. 2,839 ml (cc) 8 lb. 4 oz. 3,744 grams
> H. 3,312 ml (cc) 9 lb. 10 oz. 4,388 grams
> I. 3,785 ml (cc) 11 lb. 4,992 grams
> J. 5,678 ml (cc) 16 lb. 8 oz. 7,488 grams
> K. 7,570 ml (cc) 22 lb. 9,984 grams
> L. 9,463 ml (cc) 27 lb. 8 oz. 12,480 grams
> M. 11,356 ml (cc) 33 lb. 14,976 grams
>
> Example: 946 ml water + 1,248 grams dry plaster =3D 1,330 cc mixed =20
> plaster.
> Final mix will yield approximately 1.4 times the volume of water.
>
> Use centimeters to measure your container, Length * Width * Height
>
> So if your area is 22.5 * 11.3 * 6.4 =3D 1627.2
> You could mix up quantities in in line "D" (you will have plenty of =20=
> extra)
> or you could divide 1627.2 by 1.4 which will yield 1,162 and use =20
> quantities
> in line "C" which will give you extra but not way to much extra. =20
> Have a
> container ready to pour any extra plaster mixture into to create =20
> hump molds.
>
> We measured out both water and plaster then poured plaster into our =20=
> water
> and let soak for 2 minutes, then mixed gently for 2-3 minutes then =20
> poured.
>
> Hope this helps you,
>
> Cindy Reed
> Greenville, NC
>
>
>
> On 9/14/07 4:15 PM, "Ingeborg Foco" wrote:
>
>> Dear Charlie,
>>
>> Yes, I am using Pottery Plaster #1 and I need to pour my wedging =20
>> table. I
>> have been to the USG site several times and have emailed/spoken to =20=
>> their
>> customer service rep. They are quite helpful and so is their web =20
>> site but
>> no where did I find a chart on how to figure the volume of poured =20
>> plaster.
>>
>> I've been cautioned to be sure to weigh the water rather than =20
>> measure, weigh
>> the plaster, mix it with a certain type of paddle (which I =20
>> purchased) not to
>> over fill the container,hold
>> the paddle at a certain angle and have both the water and the =20
>> plaster at a
>> certain temperature etc etc. It all sounds rather technical =20
>> compared to the
>> way I usually mix small batches. I forget now how cool it was =20
>> supposed to
>> be but living in SW Florida makes it pretty hard to have everything
>> chilled. (my studio does not have AC and the water is like bath =20
>> water. I
>> hope to make this a monolithic pour and unless I can figure out =20
>> how to time
>> things I will most likely have to enlist help to get that kind of =20
>> quantity
>> poured all at once.
>>
>> I thank you for your help and calculations...maybe you would like =20=
>> to come
>> and help me pour the slab? :) I suppose I could find volunteers =20
>> from the
>> North about January. Unfortunately, I need to pour my table =20
>> within the next
>> couple of weeks.
>>
>> Again thanks
>>
>> Sincerely,
>>
>> Ingeborg
>>
>> thepottersworkshop.com
>>
>>
>>
>> On 9/14/07, Charlie Cummings wrote:
>>>
>>> Ingeborg,
>>>
>>> I'm assuming you want an absorbent slab and that you are using
>>> pottery plaster #1 at a consistency of 70.
>>>
>>> Multiply the dimensions and divide the total by 80. This will tell
>>> you how many quarts of water you need.
>>>
>>> 33 x 33 x 2 =3D 2178 cubic inches
>>>
>>> 2178 cubic inches / 80 cubic inches per quart water =3D 27.2 quarts.
>>>
>>> The proportion of plaster to water is- 1248g/quart
>>>
>>> You'll need 33945grams or 33.7 kilos ( x 2.2lb/kilo =3D 74.13 =
pounds)
>>>
>>> I would probably round up to 30 quarts to be sure there was
>>> extra. That means you need 82 pounds of plaster.
>>>
>>>
>>> USG pottery plaster #1 information
>>> http://www.gypsumsolutions.com/application.asp?prod=3D49&app=3DCeramic=
s
>>> Click on the "Gypsum Products Consistency Calculator "
>>>
>>> Charlie Cummings
>>>
>>>
>>> At 08:33 AM 9/14/2007, you wrote:
>>>> Hi Clay People,
>>>>
>>>> Can someone please tell me how to calculate the quantity of plaster
>>>
>>>
>>> Charlie Cummings Clay Studio & Gallery
>>> 4130 South Clinton Street
>>> Fort Wayne, IN 46806
>>> Charlie@claylink.com
>>> 260-458-9160
>>> www.claylink.com
>>>
>>>
>>>
> ______________________________________________________________________=20=
> _______>>
> _
>>>
>>
>> _____________________________________________________________________=20=
>> _________
>> 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 =20
>> melpots2@visi.com
>
> ______________________________________________________________________=20=
> ________
> 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 =20
> melpots2@visi.com
> =01
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