Carol Tripp on sat 20 apr 02
I am trying to make some new plaster slabs to drain/dry out clay slops on.
I made two a few years ago and one is broken and the other too small.
Anyway, I "winged" it - like I did a few years ago - and just poured the
gypsom into the water, mixed and poured it out into an old drawer lined with
plastic. The plaster set but not hard - I could gouge it with my stubby
fingernail. Ah-ha, I thought, it's the type of gypsom. Backtrack here; I
live in Dubai and there are three types of gypsom available; one from Jebel
Ali, one from another emirate and one from Iran. So, I bought a different
type (50 lbs for under $3) and the same thing happened, even after several
tries. So, back to the shop and another bag, this time Iranian, which is
supposedly the best, though is costs even less than the local stuff. This
time, I read Vince's book, measured the water, the plaster, sifted it in,
used my watch,etc.- all by the book, except the gypsom - and, drum roll, I
can gouge this one with my fingernail too. None of them set up hard yet
porous like my original slabs.
I'd be grateful for any ideas.
Best regards,
Carol
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Roger Korn on sat 20 apr 02
I've had this experience with "old" plaster. The problem is that it is not
completely calcined. It eventually will get just as hard, but it can take
weeks.
You might try going to the hard end of the mix scale, say 65 parts water to
100
parts plaster and see if that mix hardens harder faster.
Not sure this is the problem, but it's an educated guess.
Roger
Carol Tripp wrote:
> I am trying to make some new plaster slabs to drain/dry out clay slops on.
> I made two a few years ago and one is broken and the other too small.
> Anyway, I "winged" it - like I did a few years ago - and just poured the
> gypsom into the water, mixed and poured it out into an old drawer lined
with
> plastic. The plaster set but not hard - I could gouge it with my stubby
> fingernail. Ah-ha, I thought, it's the type of gypsom. Backtrack here; I
> live in Dubai and there are three types of gypsom available; one from
Jebel
> Ali, one from another emirate and one from Iran. So, I bought a different
> type (50 lbs for under $3) and the same thing happened, even after several
> tries. So, back to the shop and another bag, this time Iranian, which is
> supposedly the best, though is costs even less than the local stuff. This
> time, I read Vince's book, measured the water, the plaster, sifted it in,
> used my watch,etc.- all by the book, except the gypsom - and, drum roll, I
> can gouge this one with my fingernail too. None of them set up hard yet
> porous like my original slabs.
> I'd be grateful for any ideas.
> Best regards,
> Carol
>
> _________________________________________________________________
> Chat with friends online, try MSN Messenger: http://messenger.msn.com
>
>
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--
Roger Korn
McKay Creek Ceramics
In AZ: PO Box 463
4215 Culpepper Ranch Rd
Rimrock, AZ 86335
928-567-5699 <-
In OR: PO Box 436
31330 NW Pacific Ave.
North Plains, OR 97133
503-647-5464
Mark Potter on sat 20 apr 02
Carol, Just a thought, and may be something you've already considered. The
plaster you are buying sounds like it is formulated for wall plastering and
building resurfacing. They use a great quantity of plaster for exteriors in
dry countries, where with paint, it holds up very well. It is very low grade
though. You need to get someone to go to the market or bazaar and get
Plaster of Paris. It is definitely harder, and definitely quicker setting so
be prepared. Normally I would say Plaster of Paris is too hard, and doesn't
absorb enough water for pottery purposes, but it is close enough and if
plaster in general where you are is of less quality, then I would ask for
it.
But - a sharp fingernail can gouge even Plaster of Paris, especially when
wet.
-----Original Message-----
From: Ceramic Arts Discussion List [mailto:CLAYART@LSV.CERAMICS.ORG]On
Behalf Of Carol Tripp
Sent: Saturday, April 20, 2002 1:18 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: plaster won't cure properly problem
I am trying to make some new plaster slabs to drain/dry out clay slops on.
I made two a few years ago and one is broken and the other too small.
Anyway, I "winged" it - like I did a few years ago - and just poured the
gypsom into the water, mixed and poured it out into an old drawer lined with
plastic. The plaster set but not hard - I could gouge it with my stubby
fingernail. Ah-ha, I thought, it's the type of gypsom. Backtrack here; I
live in Dubai and there are three types of gypsom available; one from Jebel
Ali, one from another emirate and one from Iran. So, I bought a different
type (50 lbs for under $3) and the same thing happened, even after several
tries. So, back to the shop and another bag, this time Iranian, which is
supposedly the best, though is costs even less than the local stuff. This
time, I read Vince's book, measured the water, the plaster, sifted it in,
used my watch,etc.- all by the book, except the gypsom - and, drum roll, I
can gouge this one with my fingernail too. None of them set up hard yet
porous like my original slabs.
I'd be grateful for any ideas.
Best regards,
Carol
_________________________________________________________________
Chat with friends online, try MSN Messenger: http://messenger.msn.com
____________________________________________________________________________
__
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
melpots@pclink.com.
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