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Chantay

Making molds from Styrofoam

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Chantay    101

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

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Mark C.    1,798

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

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Lucille Oka    16

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.

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BeckyH    42

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.

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Marcia Selsor    1,301

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

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Chantay    101

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

 

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Chris Campbell    1,086

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?

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tjbanjo    1

I made a form from blue building insulation foam and now I'd like to make a plaster negative mold from it. I think I'd rather do that than coat it with plaster and use it as a hump mold. I'm assuming that since it's a bit porous I should coat it with something. Will petroleum jelly or dish soap work? If I use petroleum jelly, what do I use to clean it off of the foam once I've made the mold?

Thanks,

Bob

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bciskepottery    925

I don't believe the blue (or pink) insulation foam is porous. In any case, I use Murphy's Soap as a mold release, just wipe the surface of the blue mold and you should be okay.

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Mart    23

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?

 

... for porcelain.

Everything else can be done with a regular plaster form hardware/building supply store.

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bciskepottery    925

Liquid dish soap should work okay.  You could spray with Pam or similar spray vegetable oil.  You want something that will goes on smoothly and does not leave marks or create ridges, lines in the plaster.  I don't recommend vasoline or petroleum jelly . . . to hard to clean up afterwords. 

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Mossyrock    29

I don't believe the blue (or pink) insulation foam is porous. In any case, I use Murphy's Soap as a mold release, just wipe the surface of the blue mold and you should be okay

The blue insulation foam has a protective plastic film that would keep it from being porous, but even if it was removed, the foam has a tight smooth surface.  I use it with concrete and have to rough up the surface a bit to get the concrete to adhere to it.

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TJR    359

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

 

Marcia

Marcia;

Bill Daley came up to do a workshop at my old art school. He used cardboard and duct tape. We all made these huge slab pots. He was a great guy, and a great teacher.I didn't see any styrofoam.

TJR.

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TJR    359

I buy the pink one inch thick styrofoam from Home Depot. It is 2ft by 8 ft. I have made a lot of press molds in various sizes with it, and can reuse them. I did not coat them with plaster, but the foam is pretty dense.

TJR.

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Marcia Selsor    1,301

 

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

Marcia

 

Marcia;

Bill Daley came up to do a workshop at my old art school. He used cardboard and duct tape. We all made these huge slab pots. He was a great guy, and a great teacher.I didn't see any styrofoam.

TJR.

That was back in the 60s. last time I saw himI was his assistant at Archi Bray and he was teaching tarpaper molds. He is a great slab builder...whatever he is using!

Marcia

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stephsteph    23

you may encounter drawbacks with 'plaster of paris', if you are making large molds that need to be strong or molds that  have a lot of detail which would need to hold up through several pressings. i pound clay into molds, which  wears them down faster than if i were draping clay over or in them.

so i like to use either ceramical (very strong: you can make thinner, larger, lighter weight molds, but the plaster does not absorb water as much as pottery plaster so you may need to use cornstarch , etc  for easy release:

or Duramold (doesn't use as much water as pottery plaster, isn't quite as porous but releases well, is also a bit stronger, has small fibers in it so detail hold up very ,very well, even with many pressings.

 

'consistency' is the term used to tell you how much water  to use per unit of plaster

pottery plaster number 1 has a consistency of 70, AKA 70 parts water to 100 parts plaster

ceramical: consistency of 45 . 45 parts water to 100 parts plaster

duramold :consistency of 60-65.

local plaster of paris :look for any info to give you an idea of ratio. may not be rated.

 

incorporating foam into the moldmaking process is a great weight and time saver, whether the foam is used as a model for a plaster mold or used in conjunction with a plaster coating to make the mold itself.

 

 

like Marcia said though, if it is working for you for the types of molds you make and  for your processes, no need to change!

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tjbanjo    1

 

I don't believe the blue (or pink) insulation foam is porous. In any case, I use Murphy's Soap as a mold release, just wipe the surface of the blue mold and you should be okay

The blue insulation foam has a protective plastic film that would keep it from being porous, but even if it was removed, the foam has a tight smooth surface.  I use it with concrete and have to rough up the surface a bit to get the concrete to adhere to it.

 

I'm actually using the foam as the model and casting a plaster mold from it. Sorry if I wasn't clear about that. I carved half a vase from the blue foam and sanded it a little to smooth off the uneven parts, so the foam no longer has the plastic film or that nice, smooth surface that the original outside surfaces have when you get it.

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