Hendrix, Taylor J. on mon 10 feb 03
Hello all:
I am making a clay run to Austin on Wednesday
with my teacher. We are going to stock up on
clay and glaze materials. I want to get a 50#
bag of plaster and make some replacement bats
for her wedging table as well as some for me.
Right now she has two slabs about 15" by 24"
by 2" thick, one for dark clay, one for light.
They are pretty pitted and cracked.
Whatdo folks recommend for the plaster or hydro cal
or the like for this application? Will I need
to reinforce the slabs in some way? They will
be resting on a wooden table, pretty rigid.
It will probably be a 50# pound bag, so I don't
think I will be using the bag up making four or
so bats. I will also be making some hump/slump
molds I guess, to use up the remainder. Maybe
even some bats for the wheel! Any ideas to
think about would be helpful in making a choice.
I'm certain Armadillo has a selection of plasters.
Taylor, in Waco
John Rodgers on wed 12 feb 03
To work with plaster for most any reason, I would encourage you to get a
plaster calculator for your plaster supplier or call US Gypsum in
Chicago and request one be sent to you. It is a bit like a cardboard
slide rule, but includes all of USG's products, and helps you calculate
how much plaster and how much water for any shaped volume and any given
USG product.
For absorption purposes I use #1 Pottery Plaster from USG (U.S. Gypsum
Corporation). There are other brand names, but I like the USG stuff.
Hydrocal, while strong, would not have the absorbing qualities you need
for the clay wedging, unless you specifically want to wedge with little
water absorption.
UltraCal would not work well for the same reason. Very hard, very dense.
I make my wedging tables upside down.
I make a table that is basically an open frame constructed out of 2X4 or
2X6 lumber.
For the bottom side of the frame I prepare 4 triangle shaped pieces of
plywood to serve as gussets on each corner and provide an anchor for
table leg hardware.
Centered in each triangle I attach a standard pipe flange sized to
accept a piece of 2 inch black iron pipe (galvanized works - I'm just
cheap)
I do a few calculations to get the working height right, and have a
plumbing shop cut four black iron pipe sections of the right length.
Threads are cut on one end only. A rubber plumbing cap is installed on
the unthreaded end and secured with a large stainless hose clamp. When
the table is completed with the plaster installed, the legs are
installed into the pipe flanges and the table is turned right side up.
I place the table frame, bottom up, on a level counter or table with a
plastic laminate top cover. This allows ease of casting and removal of
the finished table. By casting upside down against a very smooth
surface, the finished surface of the wedging table will be very smooth.
Next I seal the frame to the counter using oil based clay. This prevents
any plaster leaks on casting.
Next I make casting marks around the inside of the frame. This is my
casting level for the plaster, and also the dimensions I use allow me to
install supports for the plaster after the plaster is cast. Sometimes I
will use 2"X4" for support, sometimes 3/4" material. For a 3/4" piece of
support material I make a mark to a point 3/4" down the side of the 2X4
frame, 1-1/2" for a 2X4 (2X4's are actually 1.5X3.5).
I then coat the insides of the frame with vaseline. Be careful not to
get any on the plastic laminate below. You don't want any on the
finished plaster surface. The vaseline allows the plaster to easily pull
away from the frame as it dries and shrinks slightly.
Now I cast plaster up to the casting marks. I usually do my casting on a
table so I can bump it a bit to get it to jiggle and make the plaster
settle level.
As soon as the plaster is set, I install the supports tightly against
the back of the plaster, putting screws through the sides of the frames
into the ends of the supports. The screw holes could be pre-drilled
before casting to aid installation.
Next I enlist some help, and lift the new wedging table slightly, away
from the counter top, and slide some wood supports under the edges. If
this is done as soon as the plaster sets and while still warm from
hydration, it is easier to remove from the table top. The moisture that
accumulates between the counter top and the plaster table makes it
easier to remove. If you wait, the moisture will re-absorb, and the
process will stick the table top down and make it harder to release
until it has dried significantly. The easiest way to get the release is
to bump the new table sideways just slightly to break the suction that
will be there. Then then table can be moved. I usually bump the frame
over the edge of the table or counter underneath. Releases any suction
and makes it easier to get a grip to lift. At this stage be sure to
always lift on the plaster and not just on the frame itself. It is
possible for the plaster to fall from the frame.
Once released and supported, install the triangle shaped pieces on the
corners, and turn the table up on it's edge. Install the legs and then
set it on the floor where ever you need for storage until the plaster is
dry. Do not use until it is thoroughly dried.
When the new wedging table is dry, you can attach a frame for a cutting
wire, and or install a canvas cover over it for wedging. The canvas
will protect it for a long time. Without the canvas, pitting of the
surface will occur sooner rather than later. If you install a canvas,
attach the canvas to two wooden strips first, then stretch the canvas
over the plaster by pulling the strips down over the sides and attaching
the strips to the table frame. If screws are used the tension in the
canvas can be adjusted as it stretches over time.
I have two tables of this type. One I use for regular wedging, the other
I use when recovering clay scrap. I put all my scrap in plastic buckets,
separated by type. I allow the clay to dry completely, crush it, then
sprinkle it into buckets of water, leaving it covered by a couple of
inches. After a week or so, sometimes longer, I will drain the the
excess water down to 1 inch, then with a heavy duty hand drill and
mixer, I beat the clay into a very loose pasty slurry. Next I rake all
that slurry out onto my wedging table that I use just for reclaim. It
has no canvas. I spread the clay directly on the plaster to a thickness
of 1 or 2 inches. I check it periodically and when it has dried to the
point I feel is right, it will have become a big slab, fairly solid on
one side, a bit gooey on the other. I turn the slab, and press the gooey
side down. After a while is will be of a wedging consistency. Then I
move to the canvas covered wedging table and wedge the daylights out of it.
Works well.
BTW, when the plaster in the table dries, it will weigh quite a bit
less. The pipe legs make the table very transportable. It can be
dismantled easily. Lay the table on it's side, unscrew the legs, put
the table on it's side in your van, etc, throw in the legs and go to
your demonstration, etc. Easy.
Good luck on your efforts,
John Rodgers
Birmingham, AL
Hendrix, Taylor J. wrote:
> Hello all:
>
> I am making a clay run to Austin on Wednesday
> with my teacher. We are going to stock up on
> clay and glaze materials. I want to get a 50#
> bag of plaster and make some replacement bats
> for her wedging table as well as some for me.
> Right now she has two slabs about 15" by 24"
> by 2" thick, one for dark clay, one for light.
> They are pretty pitted and cracked.
>
> Whatdo folks recommend for the plaster or hydro cal
> or the like for this application? Will I need
> to reinforce the slabs in some way? They will
> be resting on a wooden table, pretty rigid.
> It will probably be a 50# pound bag, so I don't
> think I will be using the bag up making four or
> so bats. I will also be making some hump/slump
> molds I guess, to use up the remainder. Maybe
> even some bats for the wheel! Any ideas to
> think about would be helpful in making a choice.
> I'm certain Armadillo has a selection of plasters.
>
>
> Taylor, in Waco
>
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>
Logan Oplinger on thu 13 feb 03
Hi Taylor,
As John Rodgers mentioned in his post, use the #1 pottery plaster, and
either obtain a plaster calculator, or do a search in the archives for
instructions on mixing plaster. When I did a search with Google using the
words pottery plaster mixing proportions, one of the references that came
up is:
http://www.potters.org/subject56702.htm
Another from Laguna Clay is:
http://www.lagunaclay.com/volumev/plaster.pdf
A third from USG is:
http://www.gypsumsolutions.com/usage.asp?usage=Pottery+Plaster
For making wedging bats that sit on a strong sturdy table, and provide
resistance to chipping, I have used the following method:
1. Saw in half lengthwise 2x6" lumber, to make two long pieces 2-1/4" wide
(Some lumber yards/hardware stores can do this for you). A 6 ft. length
will provide enough material to make eight pieces for two frames that
measure 15"wide by 24"long by 2-1/4" deep. These frames will measure 12"
by 21" on the inside. Cut the split lengths into shorter lengths of 15
inches and 21 inches, 4 of each. An 8 ft. length will provide enough
material for two frames measuring 24" by 27" by 2-1/4". The inside measure
will be 21" by 24" by 2-1/4" Cut the split lengths into eight equal 2 ft.
lengths
2. Using 4" or 5" drywall screws, attach the ends of pieces together.
|<-----21"---->|
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||--------------|| ^
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||--------------|| v
||--------------||--
3. Screw several 2" drywall screws around the inside of the fram at about
3" intervals. (These will support the plaster and hold it firmly to the
frame after the plaster has been poured into the frame and sets).
4. Stretch heavy canvas over the open frame on one side only to form the
top of the bat. Wrap the edges of the canvas around to the underside of
the frame and attach the canvas to the frame using heavy duty staples and a
staple gun.
5. Lay a piece of plastic sheet on a smooth, flat table, and place the
frame on the plastic, canvas side down.
6. Fill the frame with liquid plaster and allow to set for at least an hour
to form the bat. After the plaster has set, tilt the bat up on one side to
allow the plaster to dry out.
7. Lay the bat on a table, canvas side up.
Because the plaster was poured into the frame onto the underside of the
canvas, the plaster and canvas are firmly attached to each other. The
canvas helps prevent bits of plaster from getting into clay, and the canvas
is easier to clean, with much less clay dust. Also, moisture from clay
being wedged is more quickly drawn through the canvas into the plaster.
Good luck,
Logan Oplinger
Another Pacific Island
Latitude: 13.5 Longitude: -144.7
On Mon, 10 Feb 2003 23:59:35 -0600, Hendrix, Taylor J.
wrote:
>... I want to get a 50#
>bag of plaster and make some replacement bats
>for her wedging table as well as some for me.
>Right now she has two slabs about 15" by 24"
>by 2" thick, one for dark clay, one for light.
>They are pretty pitted and cracked.
>
>Whatdo folks recommend for the plaster or hydro cal
>or the like for this application? Will I need
>to reinforce the slabs in some way? They will
>be resting on a wooden table, pretty rigid.
>It will probably be a 50# pound bag, so I don't
>think I will be using the bag up making four or
>so bats.
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