jonathan byler on fri 18 jul 08
if you really want them to hold up try ceramical. one of my
coworkers uses it in his ram presses, and if it will hold up for
that, just think how long the molds will last under "normal" use.
one thing to note about plasters that have portland cement added for
extra strength is that they have a shorter guaranteed shelf life.
something like 6 months. granted, I have used old stuff before that
was kept well, and it was surprisingly durable, but would you risk
that if you were making molds that use 2 bags at $50 ea, and hours of
your time to make? probably not. much cheaper to get a fresh bag
than have a short life from your mold.
jon byler
3-D Building Coordinator
Art Department
Auburn University, AL 36849
On Jul 18, 2008, at 11:54 AM, James F wrote:
> Tim...
>
> I once contacted US Gypsum technical support on this very
> question. The short answer is that #1 Pottery Plaster is just a
> bit stronger and more durable than ordinary Plaster of Paris
> (Moulding Plaster). Your construction plaster is likely also
> Plaster of Paris, and as such has a dry strength of about 2000
> PSI. #1 Pottery Plaster has a dry strength of 2400 PSI. Molds
> made with #1 Pottery Plaster will just last a bit longer and resist
> damage a bit more than those made with Plaster of Paris. I have
> molds made with both types of plaster, and they are all holding up
> pretty well. If your molds will get heavy use, it might prove
> cheaper in the long run to use the good stuff.
>
> Hope it helps.
>
> ...James
>
>> Date: Fri, 18 Jul 2008 11:51:22 -0300
>> From: ceramista.tim@GMAIL.COM
>> Subject: Pottery Plaster #1
>> To: CLAYART@LSV.CERAMICS.ORG
>>
>> Question: What's special about Pottery Plaster #1? It is
>> expensive to
>> import here in South America, so I'm looking for ways to make my own
>> version ... until know I've been using regular construction plaster
>> (only occasionally the quick-setting kind).
>>
>> Regards,
>>
>> Tim
>
> _________________________________________________________________
> With Windows Live for mobile, your contacts travel with you.
> http://www.windowslive.com/mobile/overview.html?
> ocid=TXT_TAGLM_WL_mobile_072008
Timothy Joko-Veltman on fri 18 jul 08
Question: What's special about Pottery Plaster #1? It is expensive to
import here in South America, so I'm looking for ways to make my own
version ... until know I've been using regular construction plaster
(only occasionally the quick-setting kind).
Regards,
Tim
James F on fri 18 jul 08
Tim...
I once contacted US Gypsum technical support on this very question. The sh=
ort answer is that #1 Pottery Plaster is just a bit stronger and more durab=
le than ordinary Plaster of Paris (Moulding Plaster). Your construction pl=
aster is likely also Plaster of Paris=2C and as such has a dry strength of =
about 2000 PSI. #1 Pottery Plaster has a dry strength of 2400 PSI. Molds =
made with #1 Pottery Plaster will just last a bit longer and resist damage =
a bit more than those made with Plaster of Paris. I have molds made with b=
oth types of plaster=2C and they are all holding up pretty well. If your m=
olds will get heavy use=2C it might prove cheaper in the long run to use th=
e good stuff.
Hope it helps.
...James
> Date: Fri=2C 18 Jul 2008 11:51:22 -0300
> From: ceramista.tim@GMAIL.COM
> Subject: Pottery Plaster #1
> To: CLAYART@LSV.CERAMICS.ORG
>=20
> Question: What's special about Pottery Plaster #1? It is expensive to
> import here in South America=2C so I'm looking for ways to make my own
> version ... until know I've been using regular construction plaster
> (only occasionally the quick-setting kind).
>=20
> Regards=2C
>=20
> Tim
_________________________________________________________________
With Windows Live for mobile=2C your contacts travel with you.
http://www.windowslive.com/mobile/overview.html?ocid=3DTXT_TAGLM_WL_mobile_=
072008=
jonathan byler on fri 18 jul 08
go to this us gypsum website:
http://gypsumsolutions.com/application.asp?app=Ceramics
there you will find links to everything you ever wanted to know (and
more) about various plaster types and other gypsum products.
IIRC most of the specialty plasters (i.e. not plaster of paris) have
varying amounts of portland cement, and probably other minerals added
to affect the strength, toughness, set time, etc.
jon
jon byler
3-D Building Coordinator
Art Department
Auburn University, AL 36849
On Jul 18, 2008, at 9:51 AM, Timothy Joko-Veltman wrote:
> Question: What's special about Pottery Plaster #1? It is expensive to
> import here in South America, so I'm looking for ways to make my own
> version ... until know I've been using regular construction plaster
> (only occasionally the quick-setting kind).
>
> Regards,
>
> Tim
Jeff Gieringer on sat 19 jul 08
I would also question absorption rates. Ceramical is a nice smooth
plaster, but I wouldn't use it as a slump/hump mold material as it
has a very low absorption rate. Just a thought.
Jeff Gieringer
Gatlinburg, TN
--- In clayart@yahoogroups.com, jonathan byler wrote:
>
> go to this us gypsum website:
>
> http://gypsumsolutions.com/application.asp?app=3DCeramics
>
> there you will find links to everything you ever wanted to know (and
> more) about various plaster types and other gypsum products.
>
> IIRC most of the specialty plasters (i.e. not plaster of paris) have
> varying amounts of portland cement, and probably other minerals
added
> to affect the strength, toughness, set time, etc.
>
> jon
>
>
> jon byler
> 3-D Building Coordinator
> Art Department
> Auburn University, AL 36849
>
> On Jul 18, 2008, at 9:51 AM, Timothy Joko-Veltman wrote:
>
> > Question: What's special about Pottery Plaster #1? It is
expensive to
> > import here in South America, so I'm looking for ways to make my
own
> > version ... until know I've been using regular construction
plaster
> > (only occasionally the quick-setting kind).
> >
> > Regards,
> >
> > Tim
>
Des & Jan Howard on sat 19 jul 08
Tim
Recently out of desperation, our usual home delivery of pottery
materials was a week away, we used a few kilos of the type of plaster to
which you refer.
The drape/slump mould castings had specks of grit, & on drying had a
skin that had to be scraped off, much time & effort.
In contrast the next batch of drape/slump moulds made from the 'real
stuff' were smooth & quite porous, no fiddling.
Define 'expensive', extreme PITA is expensive to me.
Des
Timothy Joko-Veltman wrote:
> Question: What's special about Pottery Plaster #1? It is expensive to
> import here in South America, so I'm looking for ways to make my own
> version ... until know I've been using regular construction plaster
> (only occasionally the quick-setting kind).
--
Des & Jan Howard
Lue Pottery
Lue NSW
Australia
2850
02 6373 6419
Timothy Joko-Veltman on sat 19 jul 08
All: thanks for the input, info, and advice.
Bill: setting time isn't a problem, though if it were, there's not
much I can do about it: our studio water is a bit chilly, and doesn't
warm up much during the day.
Des: Expensive = $5-10 USD per KILO + S&H ... not worth it for me.
Not when I can buy a 40kg bag for around $25 USD, and it gives
reasonable results.
James: The construction plaster I use says "99% CaSO4" on it ... is
nice and smooth (if mixed well), sets hard with high proportions of
plaster to water.
Jonathan: Thank you. That site is indeed very useful. If importing
#1PP is out, importing Ceramical is, too. But if it's just a question
of doping "normal" plaster with Portland cement, then it wouldn't be
hard to do ... just need to figure out good proportions.
Regards,
Tim
jonathan byler on mon 21 jul 08
Tim,
please post if you do any experimenting re: portland cement and
plaster mixes. Would be interested to see the results, even if they
are rather subjective, especially since I have too much other stuff
on my plate at the moment.
-jon
jon byler
3-D Building Coordinator
Art Department
Auburn University, AL 36849
On Jul 19, 2008, at 12:27 PM, Timothy Joko-Veltman wrote:
> All: thanks for the input, info, and advice.
>
> Bill: setting time isn't a problem, though if it were, there's not
> much I can do about it: our studio water is a bit chilly, and doesn't
> warm up much during the day.
>
> Des: Expensive = $5-10 USD per KILO + S&H ... not worth it for me.
> Not when I can buy a 40kg bag for around $25 USD, and it gives
> reasonable results.
>
> James: The construction plaster I use says "99% CaSO4" on it ... is
> nice and smooth (if mixed well), sets hard with high proportions of
> plaster to water.
>
> Jonathan: Thank you. That site is indeed very useful. If importing
> #1PP is out, importing Ceramical is, too. But if it's just a question
> of doping "normal" plaster with Portland cement, then it wouldn't be
> hard to do ... just need to figure out good proportions.
>
> Regards,
>
> Tim
Timothy Joko-Veltman on tue 22 jul 08
Ivy, that was extremely helpful. THANK you. I will let you (all)
know how it goes (I'm going to the store tomorrow).
Regards,
Tim
On Tue, Jul 22, 2008 at 12:49 AM, iglasgo wrote:
> Tim,
> My house is about 50 miles from the nearest source of plaster of
> paris, and if I want pottery plaster or Hydrostone I have to mail
> order it, so I have had to improvise on occasion.
> To simulate Hydrostone I've mixed regular plaster of paris and
> Portland cement. I read the Hydrostone MSDS which said that it had <5%
> of Portland cement and >95% of gypsum plaster. I mixed the powders up
> in the approximate ratio dry. From that point I followed the
> directions for Hydrostone. I was moderately satisfied with the result.
> Even with my most careful mixing there were still gray cement spots on
> the finished product, and it was not as strong as Hydrostone. But it
> was much stronger than regular plaster. Its porosity was somewhere in
> between Hydrostone and plaster, but the cement spots were very
> non-porous and stuck to my clay. After three tries I gave up on the
> improvisation and ordered the Hydrostone. If I had to do it over again
> I would try to find another way to thoroughly mix & screen the dry
> powder without kicking up too much dust.
> Hope this helps.
> -Ivy G.
>
>
>
> --- In clayart@yahoogroups.com, Timothy Joko-Veltman
> wrote:
>>
>> All: thanks for the input, info, and advice.
>>
>> Bill: setting time isn't a problem, though if it were, there's not
>> much I can do about it: our studio water is a bit chilly, and doesn't
>> warm up much during the day.
>>
>> Des: Expensive = $5-10 USD per KILO + S&H ... not worth it for me.
>> Not when I can buy a 40kg bag for around $25 USD, and it gives
>> reasonable results.
>>
>> James: The construction plaster I use says "99% CaSO4" on it ... is
>> nice and smooth (if mixed well), sets hard with high proportions of
>> plaster to water.
>>
>> Jonathan: Thank you. That site is indeed very useful. If importing
>> #1PP is out, importing Ceramical is, too. But if it's just a question
>> of doping "normal" plaster with Portland cement, then it wouldn't be
>> hard to do ... just need to figure out good proportions.
>>
>> Regards,
>>
>> Tim
>>
>
iglasgo on tue 22 jul 08
Tim,
My house is about 50 miles from the nearest source of plaster of
paris, and if I want pottery plaster or Hydrostone I have to mail
order it, so I have had to improvise on occasion.
To simulate Hydrostone I've mixed regular plaster of paris and
Portland cement. I read the Hydrostone MSDS which said that it had <5%
of Portland cement and >95% of gypsum plaster. I mixed the powders up
in the approximate ratio dry. From that point I followed the
directions for Hydrostone. I was moderately satisfied with the result.
Even with my most careful mixing there were still gray cement spots on
the finished product, and it was not as strong as Hydrostone. But it
was much stronger than regular plaster. Its porosity was somewhere in
between Hydrostone and plaster, but the cement spots were very
non-porous and stuck to my clay. After three tries I gave up on the
improvisation and ordered the Hydrostone. If I had to do it over again
I would try to find another way to thoroughly mix & screen the dry
powder without kicking up too much dust.
Hope this helps.
-Ivy G.
--- In clayart@yahoogroups.com, Timothy Joko-Veltman
wrote:
>
> All: thanks for the input, info, and advice.
>
> Bill: setting time isn't a problem, though if it were, there's not
> much I can do about it: our studio water is a bit chilly, and doesn't
> warm up much during the day.
>
> Des: Expensive =3D $5-10 USD per KILO + S&H ... not worth it for me.
> Not when I can buy a 40kg bag for around $25 USD, and it gives
> reasonable results.
>
> James: The construction plaster I use says "99% CaSO4" on it ... is
> nice and smooth (if mixed well), sets hard with high proportions of
> plaster to water.
>
> Jonathan: Thank you. That site is indeed very useful. If importing
> #1PP is out, importing Ceramical is, too. But if it's just a question
> of doping "normal" plaster with Portland cement, then it wouldn't be
> hard to do ... just need to figure out good proportions.
>
> Regards,
>
> Tim
>
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