pat gilmartin on mon 26 jul 10
I am trying to slip cast some tiles for a table top - using a plaster
of paris mold that I made for the job. The slip seems to almost "cling"
to the edges of the mold (before it shrinks away from them), making a
rim around the back side of the tile that is significantly higher than
the interior surface. I did dampen the mold slightly before pouring the
slip. Any suggestions as to why this happens and how to prevent it?
Nancy Udell on mon 26 jul 10
Pat, to get a good cast for tiles, you need to make a two part mold.
Cast your prototype face up, but leave enough room around the tile to
make keys. Then cast the other part on top of the first, leaving
space for a funnel pour hole and air escape hole. (Don't forget to
SOAP liberally). So basically, to cast solid, you need a back.
Nancy
On Jul 26, 2010, at 1:50 PM, pat gilmartin wrote:
> I am trying to slip cast some tiles for a table top - using a plaster
> of paris mold that I made for the job. The slip seems to almost
> "cling"
> to the edges of the mold (before it shrinks away from them), making a
> rim around the back side of the tile that is significantly higher than
> the interior surface. I did dampen the mold slightly before pouring
> the
> slip. Any suggestions as to why this happens and how to prevent it?
Nancy Udell on mon 26 jul 10
Pat, also, if you want to use the one part mold, consider press
molding instead which can work quite well for tiles. Pound the clay
strongly into the mold using a scrunchie (fabric with plastic liner
with sand or grog) or other soft object. Or put a board on top and
jump on it (supporting the paster mold appropriately underneath).
Then wire off the excess and you will have a tile. I think many
including me would recommend USG pottery plaster no. 1 rather than
plaster of paris you get in the hardware store for either the slip
casting or the press molding.
Good Luck
Nancy
On Jul 26, 2010, at 1:50 PM, pat gilmartin wrote:
> I am trying to slip cast some tiles for a table top - using a plaster
> of paris mold that I made for the job. The slip seems to almost
> "cling"
> to the edges of the mold (before it shrinks away from them), making a
> rim around the back side of the tile that is significantly higher than
> the interior surface. I did dampen the mold slightly before pouring
> the
> slip. Any suggestions as to why this happens and how to prevent it?
Lis Allison on tue 27 jul 10
On July 26, 2010, you wrote:
> Pat, also, if you want to use the one part mold, consider press
> molding instead which can work quite well for tiles. Pound the clay
> strongly into the mold using a scrunchie (fabric with plastic liner
> > with sand or grog) or other soft object.
For smaller molds (up to about 8" square), I find my thumbs work best and
fastest! Start in the middle and work to the edges. A plastic drywall
scraper is great for taking the excess off the back, then when dry, sand
with a sanding block (outside or with a mask on).
Lis
--
Elisabeth Allison
Pine Ridge Studio
website: www.pine-ridge.ca
Pottery blog: www.studio-on-the-ridge.blogspot.com
Garden blog: www.garden-on-the-ridge.blogspot.com
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