[Wahine]

Over the holidays I came across some unusual shaped packing material made from styrofoam. I'm wondering if I can use the styrofoam forms with pottery plaster to make some molds. I don't want to mix up the plaster and not be able to use it. The pottery plaster is costing me $25 for 50lbs. Uugh.

-chantay

[Mark C.]

I would say yes if its SMOOTH not textured-plaster will get into a texture and some foam will be stuck in it. If its smooth and has some type of release (mold soap)then go for it.
Good pottery plaster around here costs $16 per 50# and that seems cheap.
Mark

[Lucille Oka]

What does it look like? Is the styrofoam a little loose or is it tight? You can always soap it up real well and try it. Can you show what you are talking about? I have seen many great looking pieces of styrofoam that look like they will make interesting objects but then the process of getting to a negative mold was too expensive and cumbersome for me to do it at this time and place. I would have used Hydrocal White which casts beautifully.

[bciskepottery]

Here is the process Steve Howell uses for making plaster molds with styrofoam . . . http://ceramicartdai...dTileHowell.pdf

[Marcia Selsor]

yes. my teacher,Bill Daley , used styrofoam molds with a coat of plaster as the basis for much of his work.

Marcia

[BeckyH]

Whaine wants to make plaster molds of the styrofoam, not use the styrofoam for making a mold. You might consider coating the pieces with a spray on polyurethane coating, giving it several layers, to seal the cracks and crevasses that styrofoam has. Try and find a better source for your plaster, that price seems high. Get us some pictures.

[Marcia Selsor]

Putting a skin of plaster over the styrofoam surface helps dry the clay enough for it to take the shape quickly and pop it off. It was something I was taught in school and used this for hand building multiple foams quickly and attaching them.
Carving the styrofoam to a shape desired, refine with a surform tool and apply a thin coat of plaster. Smooth is with a metal flexible rib as it sets up. It is a good type of mold...a positive form, not a negative form, i.e. a hump mold , not a slump mold. As such the clay needs to be removed before it starts shrinking.
Wahine said she wondered if she "can use the styrofoam forms with pottery plaster to make some molds".. If I misunderstood, sorry. This is the way I have used styrofoam and plaster to make molds.

Marcia

[Wahine]

Thanks everyone for the replies. The piece of styrofoam is square with an oval cut out. My plan was to use it to create a hump mold. It is pretty stiff. I will try soaping it very well. The plaster I'm getting is from Highwater, resold through a local studio. I don't have a good local source for pottery supplies despite a large number of potters in the area.

-chantay

[Chris Campbell]

Just had a duh moment ... I've been making molds out of styrofoam for years but never got the last step of coating it with plaster to smooth it out. Of course that would work! So many commercial packing shapes are interesting but they have logos ... the plaster bath would solve that problem for both slump and hump molds. Thanks!

Also, I just use plaster of Paris from the hardware store ... Cheap and it seems to work. My molds are only for short term use.
Can someone tell me why i should use potters plaster?

[Marcia Selsor]

Chris,
If what you are using is working for you and your needs, I can not tell you why you should use something else.

Marcia