Jeff Longtin on fri 13 sep 02
Alan said:
>When going for longer mixing times, keep a sharp eye on the mix. The first
>time I tried mixing Hydrostone for the time recommended in the USG
>literature, it hardened up right there in the mixing bucket... Use your
>head, not a blind eye on the timer. :-)
A note on plaster mixing times:
Original 50 lb. bags of plaster usually have a date printed somewhere on
them. Before mixing a large quanity it is good to check that date. This date
can help you know how much, or how little, you can mix your plaster.
Plaster that is 6 months old, or newer, tends to take longer to set up.
Plaster that is between 6 months and 1 year old mixes really well in the
proscribed timeframe. If your plaster is over 1 year old you should be
prepared for your plaster mix
to set up quickly, sometimes really quickly!
Stores that supply foundry shops tend to have the freshest plaster. Pottery
supply stores tend to have more sporadic supplies, sometimes wonderfully
fresh, sometimes woefully old.
Plaster age is the one "x" factor that you always need to consider when
working with large quanities of plaster.
Take care
Jeff Longtin
Complex Molds Made Easy
.
Ditmar on fri 13 sep 02
As an addenda to Jeff's post....
Age, AND how / where it's stored makes a big difference. A 6 month old bag I
store in Hawaii will have different setting times from a bag stored in
Arizona. Test first to be sure. .....Moisture / humidity is the culprit.
I actually love to keep around old plaster. I know it sets F-A-S-T, so I can
use it, and finish some projects that much more quickly. ( e.g. a bag of
casting plaster that sets in about 1 minute, from when it hits the water. )
-Ditmar
>
> A note on plaster mixing times:
> Original 50 lb. bags of plaster usually have a date printed somewhere on
> them. Before mixing a large quanity it is good to check that date. This
date
> can help you know how much, or how little, you can mix your plaster.
> Plaster that is 6 months old, or newer, tends to take longer to set up.
> Plaster that is between 6 months and 1 year old mixes really well in the
> proscribed timeframe. If your plaster is over 1 year old you should be
> prepared for your plaster mix
> to set up quickly, sometimes really quickly!
working with large quanities of plaster.
>
> Take care
> Jeff Longtin
> Complex Molds Made Easy
>
>
>
> .
>
>
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Paul Huel on mon 16 sep 02
Greetings
My experience with plaster:
I mix 1 liter of water with 1.5kg of plaster. This is pottery #1
plaster.
I try for the water temperature around 20-25 deg C. (75F). I add the
plaster to the water and let slake for 2-3 minutes then mix slowly
with my hand/arm. =20
In my experience, it takes anywhere from 5-10 minutes of mixing until
the plaster is ready to pour, somewhat more time than others have
mentioned. I think this may have something to do with the amount of
plaster being mixed and or the temperature of the water. =20
When I buy plaster, I try to get it in a 5 gallon bucket as soon as i
can to keep it from absorbing water. I haven't found that after a
year that it sets any sooner, perhaps the bucket is keeping it from
absorbing water.
Paul
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