Jonathan Kaplan on thu 2 oct 97
May, once again, offer a correction to an earlier post regarding plaster
mixing. It is important that correct information be posted on this list so
that results, at least in the case of mixing plaster whether it be for bats
or other wise, yield predictable results.
As a professional mold maker for many years using plasters of all types and
rubber materials of all types, the correct way to mix plaster is as
follows:
1. Use a volume/mix slide rule available from US Gypsum.
2. Weigh the water
3. Weigh the plaster
4. Dump the plaster into the water
5. Let the plaster slake for 2 1/2 minutes
6. Mix the plaster for 2 1/2 minutes
7. Pour the plaster, over a sharp edge to break the air. Pour into a corner
of the mold box/coddle. Do not pour directy over the model of whatever you
are making a mold of.
The 5 minute rule (2 1/2 slake, 2 1/2 mix has worked for me for many many
years.
Remember that each type of plaster has its own consistancy and this is what
needs to be observed, and why the "just sift the plaster into the water
until it mounds on top" is misinformation and while it may produce workable
results, does not take full advantage of the characteristics of plaster.
If you do it right the first time, you won't have to repeat your work.
Jonathan
Jonathan Kaplan, president jonathan@csn.net
Ceramic Design Group Ltd./Production Services
PO Box 775112
Steamboat Springs CO 80477
Plant Location (please use this address for all UPS shipments)
30800 Moffat Ave Unit 13
Steamboat Springs CO 80487
(970) 879-9139*voice and fax
http://www.craftweb.com/org/jkaplan/cdg.shtml
http://digitalfire.com/education/clay/kaplan1.htm
Evan Dresel on sat 4 oct 97
At 07:42 AM 10-2-97 EDT, Jonathan once again helped us all find the way to
better plaster. And I am all in favour of precision and above all
understanding what you are doing. So my question is why bother *weighing*
water when it is so much easier to measure it's volume. If you go metric
it's easy: One liter water weighs one kilogram. The only times I weigh
water is in measuring density and for calibrating volumetric ware and then I
apply bouyancy and temperature corrections. But I doubt you need that kind
of accuracy. Now the plaster you'd better weigh. (I still claim the key to
being a successful chemist is not so much knowing how to measure carefully
but knowing how carefully you need to measure.)
-- Evan in eastern Washington where the hop crop didn't do well this year
but grapes were much better -- got to love this alcohol-based economy.
>----------------------------Original message----------------------------
>May, once again, offer a correction to an earlier post regarding plaster
>mixing. It is important that correct information be posted on this list so
>that results, at least in the case of mixing plaster whether it be for bats
>or other wise, yield predictable results.
>
..
..
..
>2. Weigh the water
>
>3. Weigh the plaster
..
..
..
>Jonathan Kaplan, president jonathan@csn.net
>Ceramic Design Group Ltd./Production Services
>PO Box 775112
>Steamboat Springs CO 80477
>
Jonathan Kaplan on sun 5 oct 97
>----------------------------Original message----------------------------
>At 07:42 AM 10-2-97 EDT, Jonathan once again helped us all find the way to
>better plaster. And I am all in favour of precision and above all
>understanding what you are doing. So my question is why bother *weighing*
>water when it is so much easier to measure it's volume. If you go metric
>it's easy: One liter water weighs one kilogram. The only times I weigh
>water is in measuring density and for calibrating volumetric ware and then I
>apply bouyancy and temperature corrections. But I doubt you need that kind
>of accuracy. Now the plaster you'd better weigh. (I still claim the key to
>being a successful chemist is not so much knowing how to measure carefully
>but knowing how carefully you need to measure.)
>
>-- Evan in eastern Washington where the hop crop didn't do well this year
>but grapes were much better -- got to love this alcohol-based economy.
>
>>----------------------------Original message----------------------------
>>May, once again, offer a correction to an earlier post regarding plaster
>>mixing. It is important that correct information be posted on this list so
>>that results, at least in the case of mixing plaster whether it be for bats
>>or other wise, yield predictable results.
>>
We do some down and dirty volume "weighing" and it has worked so far, lo
these many years, and after making thousands of blocks, cases, and
production molds, indeed it does save some time. I like the idea of having
specific containers that when filled to rim(remember that old "Brim"
commercial??) hold a certain amount of material.
And I do think that there is a small degree of variation that one can apply
to correct plaster mixing techniques. For instance, at a 70 consistancy, it
takes exactly 4.2 pounds of water to set up 6 pounds of plaster. I've been
using 4 pounds of water to six pounds of plaster and it works for me. I
would however, use the caveat that it may not be prudant to push that
envelope too far. Plaster is forgiving if you understand it beforehand. It
can be very unforgiving and nasty if abused.
Rubber mold making materials are in another catagory altogether. If anyone
is interested, I'd share some notes on the flexible stuff sometime.
An awe inspring polychromatic fall here in the high country of Colorado.....
Jonathan
Jonathan Kaplan http://www.craftweb.com/org/jkaplan/cdg.shtml
http://www.ceramicsoftware.com/education/clay/kaplan1.htm
jonathan@csn.net
Ceramic Design Group Ltd./Production Services Voice:
970-879-9139 POB 775112
FAXmodem: same
Steamboat Springs, Colorado 80477, USA CALL before faxing
Plant Location: 30800 Moffat Avenue #13 Steamboat Springs Co 80487
(please use this address for all UPS, courier, and common carrier
shipments)
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