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mixing plaster

updated wed 11 apr 07

 

Elaine Beaufait on mon 27 mar 00

This is my first communication on this list. After reading all the great
responses to other questions I feel confident someone can help me out
here. I am looking to create a wedging table. The size of the structure
is 28 x 32 x 2.5. This is an old counter that I am having the sides
added to. My question is how to mix the plaster. Anything I need to be
aware of. I believe someone said it is tricky but I forgot who said it
and just what did they mean??

Thanks
Elaine Beaufait
Hudson, NY

John Rodgers on tue 28 mar 00

You would be safe to mix at a ratio of 1.5 to 1, ie 1.5 lbs plaster to 1 lb
of water. If you use USG #1 Pottery plaster that ratio will give you a
density of about 72, which is plenty good for a wedging table.

John Rodgers
In Alabama where a cold front just passed through cooling everything off.

Elaine Beaufait wrote:

> ----------------------------Original message----------------------------
> This is my first communication on this list. After reading all the great
> responses to other questions I feel confident someone can help me out
> here. I am looking to create a wedging table. The size of the structure
> is 28 x 32 x 2.5. This is an old counter that I am having the sides
> added to. My question is how to mix the plaster. Anything I need to be
> aware of. I believe someone said it is tricky but I forgot who said it
> and just what did they mean??
>
> Thanks
> Elaine Beaufait
> Hudson, NY

Claude Stephens on tue 28 mar 00

Elaine,
Something you may want to think about is deviding you wedging table top
in two sections. This is if you intend to work with both red and white clay
bodies. This way your nice whites won't pick up the iron the red body will
surely leave at least a bit of behind. Just install a 1x2 strecher piece
before pouring. As for the plaster I wish I had asked your question before I
built mine. Just a thought. Claude

Richard Gilbert on wed 29 mar 00

Elaine,
Have you considered wood instead of plaster? Plaster is harder to clean if
you are wedging different colors of clay. Plaster also tends to dry your
clay out too quickly and make it short.
An untreated wood surface requires no replacement.
Richard Gilbert
Cherryville, NC


Elaine Beaufait wrote:

> ----------------------------Original message----------------------------
> This is my first communication on this list. After reading all the great
> responses to other questions I feel confident someone can help me out
> here. I am looking to create a wedging table. The size of the structure
> is 28 x 32 x 2.5. This is an old counter that I am having the sides
> added to. My question is how to mix the plaster. Anything I need to be
> aware of. I believe someone said it is tricky but I forgot who said it
> and just what did they mean??
>
> Thanks
> Elaine Beaufait
> Hudson, NY

Joanne L. Van Bezooyen on wed 29 mar 00

How much does a pound of water weigh?

John Rodgers wrote:

> ----------------------------Original message----------------------------
> You would be safe to mix at a ratio of 1.5 to 1, ie 1.5 lbs plaster to 1 lb
> of water. If you use USG #1 Pottery plaster that ratio will give you a
> density of about 72, which is plenty good for a wedging table.
>
> John Rodgers
> In Alabama where a cold front just passed through cooling everything off.
>
> Elaine Beaufait wrote:
>
> > ----------------------------Original message----------------------------
> > This is my first communication on this list. After reading all the great
> > responses to other questions I feel confident someone can help me out
> > here. I am looking to create a wedging table. The size of the structure
> > is 28 x 32 x 2.5. This is an old counter that I am having the sides
> > added to. My question is how to mix the plaster. Anything I need to be
> > aware of. I believe someone said it is tricky but I forgot who said it
> > and just what did they mean??
> >
> > Thanks
> > Elaine Beaufait
> > Hudson, NY

Jeff Lawrence on wed 29 mar 00


Elaine Beaufait was asking about plaster:
My question is how to mix the plaster. Anything I need to be
aware of. I believe someone said it is tricky but I forgot who said it
and just what did they mean??

Thanks
Elaine Beaufait
Hudson, NY

Hello Elaine,

My best tip is to weigh the water and the plaster according to mfr
suggestions. Too much plaster and you'll get a hard non-absorbent cast. Too
much water and you'll get punky plaster that wears away quickly.

My next best tip is to wear rubber gloves from the getgo. Split ends are bad
enough in your hair -- on your fingers they're the pits!

Some other pearls:
- Sift the plaster into the water and let slake for a couple of minutes.
Slaking means you can walk away and do something else for a bit -- it allows
the plaster and water to commingle in peace. Sometimes I slake for 10
minutes and no harm done and sometimes I get caught up in something else and
slake for 20 minutes. At 20 minutes it gets thick pretty fast.

- Mix with a drill for 2 minutes, then with a stick or something for 30
seconds to let air bubbles escape. Of course, you'll put air back in when
you pour it, but you must cling to the belief that there'll be less in there
for that ritualistic 30 seconds.

- Pour when the surface starts to show tracks of the stirring stick -- It'll
be about heavy cream consistency. If you pour slowly into a corner and let
the puddle spread, you should be able to avoid adding much more air.

- Clay your seams or you'll be cleaning plaster off the floor!

Have fun! plaster is a lovely material.


Jeff Lawrence ph. 505-753-5913
Sun Dagger Design fx. 505-753-8074
18496 US HWY 285/84 jml@sundagger.com
Espanola, NM 87532 www.sundagger.com

john a gibson on wed 29 mar 00

Elaine, if you multiply width times lenth times height you will have the
number of cubic inches in your area. Then divide by 81. 81 cubic inches
in a quart of water. This will tell you how many quarts of water your
area will hold. once you have the number of qts. then decide how many
pounds of plaster per qt. it is recommended any where from 2.5 to 3.0.
by the plaster co. 2.0 lbs. works well.

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Pierre Brayford on fri 31 mar 00


-----Original Message-----
From: Joanne L. Van Bezooyen
To: CLAYART@LSV.UKY.EDU
Date: 29 March 2000 23:04
Subject: Re: Mixing Plaster


A useful mnemonic from my childhood " A pint of water weighs a pound and a
quarter."
You'll have to work it back the other way to get a pound of water.

>----------------------------Original message----------------------------
>How much does a pound of water weigh?
>
>John Rodgers wrote:
>
>> ----------------------------Original message----------------------------
>> You would be safe to mix at a ratio of 1.5 to 1, ie 1.5 lbs plaster to 1
lb
>> of water. If you use USG #1 Pottery plaster that ratio will give you a
>> Elaine Beaufait wrote:
>>

Tom Eastburn on sat 1 apr 00

Doesn't a pound of water = 1 pound? Don't we have fun.

----- Original Message -----
From: Pierre Brayford
To:
Sent: Friday, March 31, 2000 3:21 PM
Subject: Re: Mixing Plaster


> ----------------------------Original message----------------------------
>
> -----Original Message-----
> From: Joanne L. Van Bezooyen
> To: CLAYART@LSV.UKY.EDU
> Date: 29 March 2000 23:04
> Subject: Re: Mixing Plaster
>
>
> A useful mnemonic from my childhood " A pint of water weighs a pound and
a
> quarter."
> You'll have to work it back the other way to get a pound of water.
>
> >----------------------------Original message----------------------------
> >How much does a pound of water weigh?
> >
> >John Rodgers wrote:
> >
> >> ----------------------------Original
message----------------------------
> >> You would be safe to mix at a ratio of 1.5 to 1, ie 1.5 lbs plaster to
1
> lb
> >> of water. If you use USG #1 Pottery plaster that ratio will give you a
> >> Elaine Beaufait wrote:
> >>

Earl Brunner on sat 1 apr 00

Hmmm. Wouldn't a pound of water weigh about 16 ounces?
Humor
doesn't come across on this list very well, You are joking
right?
Less subtlety.......

Pierre Brayford wrote:
>
> ----------------------------Original message----------------------------
>
> -----Original Message-----
> From: Joanne L. Van Bezooyen
> To: CLAYART@LSV.UKY.EDU
> Date: 29 March 2000 23:04
> Subject: Re: Mixing Plaster
>
> A useful mnemonic from my childhood " A pint of water weighs a pound and a
> quarter."
> You'll have to work it back the other way to get a pound of water.
>
> >----------------------------Original message----------------------------
> >How much does a pound of water weigh?
> >
> >John Rodgers wrote:
> >
> >> ----------------------------Original message----------------------------
> >> You would be safe to mix at a ratio of 1.5 to 1, ie 1.5 lbs plaster to 1
> lb
> >> of water. If you use USG #1 Pottery plaster that ratio will give you a
> >> Elaine Beaufait wrote:
> >>

--
Earl Brunner
http://coyote.accessnv.com/bruec
mailto:bruec@anv.net

Wade Blocker on mon 3 apr 00



----------
> From: Earl Brunner
> To: CLAYART@LSV.UKY.EDU
> Subject: Re: Mixing Plaster
> Date: Saturday, April 01, 2000 1:22 PM
>
> ----------------------------Original message----------------------------
> Hmmm. Wouldn't a pound of water weigh about 16 ounces?
> Humor
> doesn't come across on this list very well, You are joking
> right?
> Less subtlety.......
>
> Pierre Brayford wrote:
> >
> > ----------------------------Original
message----------------------------
> >
> > -----Original Message-----
> > From: Joanne L. Van Bezooyen
> > To: CLAYART@LSV.UKY.EDU
> > Date: 29 March 2000 23:04
> > Subject: Re: Mixing Plaster
> >
> > A useful mnemonic from my childhood " A pint of water weighs a pound
and a
> > quarter."
> > You'll have to work it back the other way to get a pound of water.
> >
> > >----------------------------Original
message----------------------------
> > >How much does a pound of water weigh?
> > >
> > >John Rodgers wrote:
> > >
> > >> ----------------------------Original
message----------------------------
> > >> You would be safe to mix at a ratio of 1.5 to 1, ie 1.5 lbs plaster
to 1
> > lb
> > >> of water. If you use USG #1 Pottery plaster that ratio will give you
a
> > >> Elaine Beaufait wrote:
> > >>
>
> --
> Earl Brunner
> http://coyote.accessnv.com/bruec
> mailto:bruec@anv.net

Joanne's mnemonic refers to the weight of an English pint.
Mia in ABQ

Valerie Hawkins on mon 1 oct 01


One other tip that I've read but not tried yet - line your mixing bucket
with a plastic bag. When your finished you can just pull it out and put
into the garbage. Don't need to sacrifice a glaze bucket if your careful!

Nanci Bishof on mon 1 oct 01


Try building/renovation sites for lots of free empty 5 gallon buckets of
drywall compound. Thats what I use to mix large batches of plaster. For
smaller batches (~ 2500 g) I use an inexpensive plastic paint pail. It rinses
really clean with the garden hose.

nanci

Marni Turkel on sat 7 apr 07


Hi Bruce,

If your plaster has enough things in it that you feel the need to
sieve it, it is generally not worth using. Good plaster feels like
flour with no little "rocks".

Using water that is warmer will slow down the set time, but in the
end bad plaster is bad plaster. I use water that is close to body
temperature, doesn't feel cold, doesn't feel hot. I mix with a drill
for about 30 seconds and then hand mix for a bit. If you have a film
of water on top of the casting while it is setting up, you need to
mix longer. I can't imagine mixing Pottery Plaster #1 for 9 minutes,
or even 3.

If you need really wear resistant molds, you might try Puritan
plaster. It is used for jiggering molds and is very hard, wear
resistant, designed for molds. The problem I found with it is that it
is not generally in high demand and what I got was already old.

Marni

--
Marni Turkel

2080 Llano Rd 1B
Santa Rosa, CA 95407
Phone 707-579-5567
Fax 707-579-1116

Frank Colson on sun 8 apr 07


Hey! All you mixed up plaster mixers! Set up time for plaster, hydrocal,
ultracal and hydrostone all goes faster with "warm" water. If you want to
slow down the action, add some vinegar into the water before adding plaster!

Frank Colson
----- Original Message -----
From: "John Jensen"
To:
Sent: Sunday, April 08, 2007 6:12 AM
Subject: Re: Mixing plaster


> Marni;
> Did you mean to say that warmer water sets slower? My experience is
> that using warmer water will speed up the chemical reaction which
> leads to setting.
>
> John Jensen, Homewood Pottery
> homewoodpottery.com
> johnjensen@homewoodpottery.com
>
>> -----Original Message-----
>>On Behalf Of Marni
>> Turkel
>> Subject: Re: Mixing plaster
>>
>> Hi Bruce,
>>
>> If your plaster has enough things in it that you feel the need to
>> sieve it, it is generally not worth using. Good plaster feels like
>> flour with no little "rocks".
>>
>> Using water that is warmer will slow down the set time, but in the
>> end bad plaster is bad plaster. I use water that is close to body
>> temperature, doesn't feel cold, doesn't feel hot.
>
> ______________________________________________________________________________
> 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.

John Jensen on sun 8 apr 07


Marni;
Did you mean to say that warmer water sets slower? My experience is
that using warmer water will speed up the chemical reaction which
leads to setting.

John Jensen, Homewood Pottery
homewoodpottery.com
johnjensen@homewoodpottery.com

> -----Original Message-----
>On Behalf Of Marni
> Turkel
> Subject: Re: Mixing plaster
>
> Hi Bruce,
>
> If your plaster has enough things in it that you feel the need to
> sieve it, it is generally not worth using. Good plaster feels like
> flour with no little "rocks".
>
> Using water that is warmer will slow down the set time, but in the
> end bad plaster is bad plaster. I use water that is close to body
> temperature, doesn't feel cold, doesn't feel hot.

stephani stephenson on tue 10 apr 07


a few comments
warm water speeds up setting.cold water slows it down.

you should not have to sift plaster. if it is fresh it
will dissolve well and will not have any hard
kernels.
if there is ANY plaster ANYWHERE, that has already
'gone off', such as hard kernels in the bag or old
plaster in the cracks or crevices of the bucket, it
may act as an accelerator for the new batch...keep
clean buckets. you can spray buckets with WD 40. also
when you clean them do not scratch them. it provided
places for the old plaster to remain, and affect new
batches.

large batches of plaster (say ones that fill up a five
gallon container or larger, may go off sooner than
small batches.

nevertheless with fresh plaster you should have no
problem meeting the time guidelines.
in general the softer plasters such as pottery #1 seem
to be touchier about time (usually recommended as 4
minutes slake and 4 minutes mix)
the gypsum cement 'plasters' such as hydrocal
(ceramical, etc.)
generally have longer slake and mix times ( 8 minutes
each)
and i have even mixed them for upwards of 15 - 20
minutes for specific purposes. the seem to even thin
out about 5 minutes into the process, and these gypsum
cements, in my unscientific yet experienced view, seem
to last longer in the bag as well as easily meet the
longer mixing times for increased strength.
ditto on recommendations for frith and USG mixing
guide
Stephani Stephenson
http://www.revivaltileworks.com



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amamenec@lineone.net on tue 10 apr 07


Never heard of using vinegar in plaster before...what does the vinegar=20
do to the plaster exactly, and are there long term effects...such as=20
reducing efforvessence (sp?) perhaps?

Ama Menec, Totnes, Devon, UK.

>----Original Message----
>From: artact@COMCAST.NET
>Date: 09/04/2007 6:57=20
>To:
>Subj: Re: Mixing plaster
>
>Hey! All you mixed up plaster mixers! Set up time for plaster,=20
hydrocal,
>ultracal and hydrostone all goes faster with "warm" water. If you=20
want to
>slow down the action, add some vinegar into the water before adding=20
plaster!
>
>Frank Colson
>----- Original Message -----
>From: "John Jensen"
>To:
>Sent: Sunday, April 08, 2007 6:12 AM
>Subject: Re: Mixing plaster
>
>
>> Marni;
>> Did you mean to say that warmer water sets slower? My experience=20
is
>> that using warmer water will speed up the chemical reaction which
>> leads to setting.
>>
>> John Jensen, Homewood Pottery
>> homewoodpottery.com
>> johnjensen@homewoodpottery.com
>>
>>> -----Original Message-----
>>>On Behalf Of Marni
>>> Turkel
>>> Subject: Re: Mixing plaster
>>>
>>> Hi Bruce,
>>>
>>> If your plaster has enough things in it that you feel the need to
>>> sieve it, it is generally not worth using. Good plaster feels like
>>> flour with no little "rocks".
>>>
>>> Using water that is warmer will slow down the set time, but in the
>>> end bad plaster is bad plaster. I use water that is close to body
>>> temperature, doesn't feel cold, doesn't feel hot.
>>
>>=20
___________________________________________________________________________=
___
>> Send postings to clayart@lsv.ceramics.org
>>
>> You may look at the archives for the list or change your=20
subscription
>> settings from http://www.ceramics.org/clayart/
>>
>> Moderator of the list is Mel Jacobson who may be reached at
>> melpots@pclink.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=20
melpots@pclink.com.
>






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