Craig Clark on sun 10 dec 06
There is something seriously amiss in that it should not need to
race to pour your plaster. Either, you are mixing you plaster for too
much time, the temperature of your water is too high, of you are using
too much plaster. I don't know if you are using the ole "....just make a
little mountain in the middle..." technique of mixing or not but the
tech with who I spoke extensively at US Gypsum said the weighing the
water and plaster, hydrocal, or hydrostone is the way to go. I been
weighing ever since. It is really quite easy and you are able to add the
plaster into the water more quickly. Following this advice solved all of
the problems that I was having.
I was also told that it is a good idea to use a mixer afixed to a
drill to do the mixing of any larger batches. I just use the 4 inch
Jiffy Mixer that I have connected to my glaze mixing drill. This works
quite well. Just mixing at a slower RPM, around 800 or so, and trying
not to entrain air into the slop.. Just work things back and forth until
you are sure you have a nice creamy solution. It will only take a little
more than a minute of so. After that, you will have several minutes, as
in more than five, to pour your plaster. It will thicken gradually, not
have an instant set if ratios are correct and the temp of the water is
in what I like to call the tepid range. Just a little warm on the wrist.
I believe the folks at US Gypsum recommend about 76 F for a mixing temp.
Not sure about the water temp though. Keep in mind that raising or
lowering the water temp does have an effect not only on the set time,
but on the strength of the plaster as well.
One other thing just came to mind. The plaster may be what is called
"seeded." This means that there are little seed like concentrations of
plaster in the bag. If this is the case the plaster is old, has already
started to react with atmoshperic moisture, and is not any good. Just
throw it away and get another bag.
Look on the side the bag and get the phone number of US Gypsum. Give
them a call and ask to speak to one of the tech folks. They may have to
call you back, but they will do so, and they are very knowlegable and
forthcoming with information.
Hope this helps
Craig Dunn Clark
619 East 11 1/2 St
Houston, Texas 77008
(713)861-2083
mudman@hal-pc.org
m.mshelomi wrote:
> I have been reading all the wedging table messages for the past several
> days.
>
> With the latest talk about inserting a jiggler, for want of a better
> word,
> would like to know what material is being used for the table. If
> plaster, I
> understand how it would work to get the air out. But, if it is plaster
> paris...
> I am not so sure.
>
> I have noticed when making anything out of pottery plaster that it is
> a race
> to
> get it from the mixing bucket into the form at exactly the right
> moment so
> it
> does not turn rock hard in the bucket that it has been mixed in. One
> moment
> it is
> a liquid and the next moment it is rock solid and giving off heat.
>
> Please explain....
>
> pottermim
>
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