Dennis Mummert on sun 18 feb 01
I'm sure almost everyone has told you this by now, but don't heat your
molds. A fan stirring up the air is my method of choice for getting
saturated molds to dry. It doesn't even have to be much air, anything to
get the air moving and changed with what is hanging around in their
vicinity. Don't let 'em freeze if they're damp, either. If they're in a
small closed room, at least open the door so you get some fresh.
-----Original Message-----
From: Ceramic Arts Discussion List [mailto:CLAYART@LSV.CERAMICS.ORG]On
Behalf Of Gordon
Sent: Sunday, February 18, 2001 5:21 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: drying plaster mold question
I have some plaster molds that were given to me to use in my
teaching.. they are old and have been stored outside... i tried them to see
how they work and the detail is fine but they took a long long time to
release.. not a good idea in a school situation where the time is
limited...I am used to mold that release in 30 minutes but these took
hours...
I was wondering if it would help if I would dry them out in the kiln for
awhile before i used them.. would they release faster? or would i just
break them...
what temperature should i use... and how long should i let them dry...i
have a computer for my kiln so I can hold a temperature.
thanks in advance for any and all help
Kathleen Gordon
Palo Alto, Ca 94301
650-328-9164
fax 650-328-9113
email:kjgordon1@homail.com
"if things seem under control then you are not going fast enough!"
Mario Andretti
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Louis Katz on sun 18 feb 01
I see no reason not to put the molds in the kiln with the lid closed and set the
kiln to slowly ramp up to 120 degrees F. Course it won't dry the molds much, and
the humidity will just condense on the oustide of your kiln wall somewhere and
probably shorten your kilns life.
Better would be to get a dehumidifier blowing into a closed rack space. We do this
for my mold making class. The temperature stays down, the humidity stays down, the
airflow stays up and we get new molds to dry in a few days. The water that comes
off the dehumidifier is used to make casting slip. Our water here is very hard.
Keep your molds closed and banded as them dry.
You have to worry not only about air temperature but radiant heat. Plaster looses
water at such a low temp 127? that even a high wattage lightbulb can creat
problems.
Louis
Gordon on sun 18 feb 01
I have some plaster molds that were given to me to use in my
teaching.. they are old and have been stored outside... i tried them to see
how they work and the detail is fine but they took a long long time to
release.. not a good idea in a school situation where the time is
limited...I am used to mold that release in 30 minutes but these took
hours...
I was wondering if it would help if I would dry them out in the kiln for
awhile before i used them.. would they release faster? or would i just
break them...
what temperature should i use... and how long should i let them dry...i
have a computer for my kiln so I can hold a temperature.
thanks in advance for any and all help
Kathleen Gordon
Palo Alto, Ca 94301
650-328-9164
fax 650-328-9113
email:kjgordon1@homail.com
"if things seem under control then you are not going fast enough!"
Mario Andretti
Ceramic Design Group on sun 18 feb 01
> I was wondering if it would help if I would dry them out in the kiln for
> awhile before i used them.. would they release faster? or would i just
> break them...
> what temperature should i use... and how long should i let them dry...i
> have a computer for my kiln so I can hold a temperature.
> thanks in advance for any and all help
Never attempt to dry plaster molds in a kiln. You will calcine the plaster
and render the mold useless.
Molds are dried in industry using dryers, not kilns. Dryers move a constant
volume of air with a known heat content and change the air in the dryers on
a calculated basis. The water content of the molds is reduced slowly over
time to a known moisture content. Some industrial standards will weigh the
mold dry, then soak the mold for a given time to increase the moisture
content in the mold. Then the mold is weighed and this will be what the
casters need to provide an ideal casting condition.
Good Luck
Jonathan
Jonathan Kaplan, president
Ceramic Design Group
PO Box 775112
Steamboat Springs CO 80477
voice and fax 970 879-9139
jdkaplan@cmn.net
info@ceramicdesigngroup.net
Plant Location:
1280 13th Street Unit 13
Steamboat Springs CO 80487
(please use this address for all deliveries via UPS, comman carrier, Fed Ex,
etc.)
"Custom design and manufacturing for the ceramic arts, giftware and pottery
industries. Molds, models, and tooling for slip casting, jiggering and
hydraulic pressing. Consultation on technical issues such as clay bodies
glazes, and kilns."
Cindy Gatto on sun 18 feb 01
DO NOT USE YOUR KILN. The kill will break up the mold at best and it will
definitely lessen the life of the mold drastically. You should never put a
plaster mold in a kiln. The only time you should try to speed up the drying
of a mold is with a mold dryer. Rather you should put it on a rack where air
can get all around it and let it dry on it's own. A little warm air may help
but only a little air should be used and make sure you strap the mold
together. Believe me I learned these things the hard way.
Sincerely:
Mark Petrin
The Mudpit
228 Manhattan Ave.
Brooklyn NY 11206
Mudpitnyc@aol.com
WWW.Mudpitnyc.com
vince pitelka on mon 19 feb 01
This has been an interesting thread, with a lot of misinformation. Jonathan
Kaplan posted the best information, since this is something he knows better
than most. If you have to dry plaster regularly, use a dry-box with a fan
and a very mild heat source. If you are in a humid climate, supercharge
your drybox with a dehumidifier, and you will dry your molds quickly but
gently. And as several people have pointed out, be sure the molds are
banded together when you dry them, to make sure they do not warp.
I have seen a lot of molds destroyed as a result of being dried in kilns.
Plaster cannot take the heat. But there are no absolutes in this regard.
We have several old Norman updraft gas kilns. The pilots are always on, and
there is a very gently heat in these kilns - perfect for drying molds - they
don't get much above 100 degrees, but it is enough to dry them in a day or
two when the kiln is not being fired.
I'd shy away from ever drying molds in electric kilns. I just ain't worth
the risk.
- Vince
Vince Pitelka
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@dtccom.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
http://www.craftcenter.tntech.edu/
Lili Krakowski on mon 19 feb 01
NO!!!! WAIT!! plaster USED to be used as a source of calcium in glazes.
Hint hint of why you should not heat it in the kiln, unless it is very
"cool" heat
However you can dry in a warm room. As you are in a school you can set
NEAR a kiln, or be extra nice-nice to the cafeteria folk:( "Oh, My! That
meatloaf was SUPERB!!!) and they might let you dry the molds near their
ovens on pizza day!
there is just a possibility that being outdoors either a fungus or just
dirt seeped in and blocked the pores. No recommendable idea how to cure
that: when I have the problem I just literally soak till the water comes
out the other side, but do not know if that reduces teh plater's life,
and I do not know how fragile these molds of your are.
Nor do I know if my "regular" fungus killer--chlorine bleach--would, would
not work SAFELY on plaster
Good luck
Lili Krakowski
Wade Blocker on tue 20 feb 01
I have been following this thread and am surprised that no one suggested
two things:
1. putting the mold on a rack and putting it out in the sun
2. putting the mold in the oven( kitchen) and setting the thermostat
to the lowest degree possible and letting the mold dry overnight.Mia in
springlike ABQ
CINDI ANDERSON on tue 20 feb 01
Kathleen
I was just reading Architectural Ceramics and Peter King says he dries his plaster
molds at 120 degrees F. Everyone here is saying you can't use a kiln, but maybe it
is because it is difficult to keep a kiln at that temperature. If you have an
electronic kiln that you can set at 120 degrees, I don't see why that wouldn't be
ok.
Cindi
Fremont, CA
Chris Stanley on tue 20 feb 01
This is a fun one! We took an old refrigerator and gutted all of the
cooling components. Next, we inserted a ceramic light socket with a
standard light bulb and wired that to a household thermostat. We set the
thermostat at 80 degrees and let the molds dry. As soon as the box hits 80,
the light shuts off! Under 80, the light comes on. Temperature vs. time is
the key. After the molds are dry, we activate them by dipping them in water
for a couple of seconds and they are good to go!
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