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Donna Roes

Substitute For Plaster

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Chris Campbell    1,081

There was a Ceramic Arts Daily posting that showed a potter using dry clay

forms as molds. She made them thick and sturdy ... the bonus was being able to

re use the clay later for another form since it had not been fired.

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Lucille Oka    16

We are looking for a substitute for plaster for making press molds. Anyone ever try cement without adding the sand?

 

 

 

If you don't mind my asking, why are you looking for a substitute for plaster? What is wrong?

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Hi Donna,

The post that Chris is referring to is on the work of Lauren Sandler. You can find it here:

http://ceramicartsda...f-unfired-clay/

 

It is also part of the free download Three Great Handbuilding Techniques, available here:

http://ceramicartsda...d-slab-methods/

 

If you're worried about plaster contaminating your clay, using these bone dry molds, or using bisque molds as Marcia suggests, could be the best solution.

 

If the weight of the plaster molds is the problem, the next issue of Pottery Making Illustrated (March April) will have an article by Jonathan Kaplan on using blue foam (the stuff used for house insulation) to make slump/ hump molds. These molds weigh a lot less than traditional plaster molds.

 

Jessica

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I use beside plaster for relief tiles also latex molds.With a slabroller the latex is pressed into the clay.It works fast but the clay must not be to soft ,otherwise the clay will stick into the mold.

 

My problem with plaster is the loss of fine details after copying a model.The plaster mold losses profile soon after intensive use.Rubber is even better then latex, it can hold much more fine detail, and is not wearing out by long use.Rubber and latex molds are not suitable for every type of model,but it is ideal to impress with a mark or design.

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Mudlark    3

We are looking for a substitute for plaster for making press molds. Anyone ever try cement without adding the sand?

 

If you are after detail retention try using Hydrocal it is more robust than pottery plaster.

Mudlark

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TheSmartCat    1

For small items I make press molds of Sculpy or Fimo. The detail is excellent and there is no shrinkage between form and mold. I use a thin layer of corn starch as a mold release.

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Donna Roes    0

We are looking for a substitute for plaster for making press molds. Anyone ever try cement without adding the sand?

 

 

 

If you don't mind my asking, why are you looking for a substitute for plaster? What is wrong?

 

We are in Panama. It is humid and plaster has a short shelf life. There is no demand for it so no one carries it. Shipping would be a problem because of the time involved. I was hoping to find another product. Our experiments with cement have been unsuccessful. We added white glue to the last try. It is taking a long time to dry.

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Donna Roes    0

I use beside plaster for relief tiles also latex molds.With a slabroller the latex is pressed into the clay.It works fast but the clay must not be to soft ,otherwise the clay will stick into the mold.

 

My problem with plaster is the loss of fine details after copying a model.The plaster mold losses profile soon after intensive use.Rubber is even better then latex, it can hold much more fine detail, and is not wearing out by long use.Rubber and latex molds are not suitable for every type of model,but it is ideal to impress with a mark or design.

 

 

The rubber and latex sound like interesting possibilities. Do you think they would work for tiles? We make tile panel repeats for walls and decorative plaques.

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JBaymore    1,432

Maybe when you factor in the value of all the time and wasted test materials going into finding an alternate solution....... that just buying the plaster (I vote for hydrocal also) would actually be cost effective?

 

best,

 

...............john

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Donna Roes    0

Maybe when you factor in the value of all the time and wasted test materials going into finding an alternate solution....... that just buying the plaster (I vote for hydrocal also) would actually be cost effective?

 

best,

 

...............john

 

 

Sounds great John, and I would love to do exactly that but plaster doesn´t seem to exist here (Panama) and the time involved in shipping (most likely a month) added to the time the dealer had it (who knows?) would make it tricky to time my production runs as I wouldn´t know how much more life I had in the plaster till it was too late. What´s the shelf life of hydrocal? Maybe shipping that would be the way to go.

Thanks for the response, I really appreciate it. A little moral support goes a long way when we get frustrated.

 

Donna

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The rubber and latex sound like interesting possibilities. Do you think they would work for tiles? We make tile panel repeats for walls and decorative plaques.

 

 

The latex works excellent for tiles and plaques.I don't have use the rubber by myself but by reading about it,I think it is better and stronger then latex.But to get the idea and have some practice it is good to start with latex.Here in holland a bottle latex is easy to buy in creative stores,but maybe where you live you can also order some latex via internet and postal service.

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Mudlark    3

Hi Donna,

When I suggested Hydrocal I assumed you lived in the USA. Another mold material that may be possible for you re the logistics problem is Automotive bog. Since this is sold in cans with the catalyst in a seperate container shelf life is not a problem. It will be dearer than plaster but the molds made from it are almost indestructable. You will need a little experimentation to get the mix right for your climate.

 

Another idea, can you get Dentists plaster ? There must be someone importing it to support the local Dentists' Technicians. Once again it is not the cheapest of solutions but there is a range of products available one of which might suit your purpose.

 

Mudlark

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The primary reason that plaster is a good mold material is because in many areas it is plentiful, inexpensive and easy to use. Probably the most important propeties of plaster is its ability to absorb water. The ability to absorb water also makes bisque a useful material to make ceramic molds that being said there are probably other techniques and materials that can be used. If you are interested in making tiles you don't need to have a lot of absorptive properties in order to duplicate the tiles. If you are capable of makig a cavity with adequate detail in a material that is tough and durable such as concrete it wold work if you use a hydraulic press and a virtually dry clay body. If you mix dry clay to a point where it will just hold togoether you can press it into a mold and then placde the mold slightly elevated and hit it with a mallet so that it releases the clay. Remember you only need to have the clay hold together long enough to place it n a kiln to vitrify it. It will vitrify at its vitrification temperature if the platelets are in adequate contact with each other.

 

Also in a very humid climate you can reconstitute plater of paris by heating it to the amount where it changes state again. Plaster is basically calcium sulphate and can be made by heating gypsum (a common mineral) to about 300 degrees F. You can also make plaster from limestone again by heating it, then grinding (pulverizing) in to a powder and re-hydrating it.

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Mudlark    3

Hi Donna,

The previous post by Hairless Potter (sounds like my condition)set me thinking. The building industry uses gypsum based products for plastering. I used some of them when I ran out of Pottery Plaster, I was adding a couple of rooms onto my house at the time and so had them handy. The building Industry will have a high turnover rate so shelf life should not be a problem also the quanties involved may have attracted local manufacture. Some ready mixed products such as Cornice Cement are available here (Australia) in small quantities and are worth experimenting with.If all else fails you could make molds from Glass Fibre although this is a dirty smelly way to do things,and is much dearer than plaster.

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terraforma    4

Donna,

 

If you can't get plaster but would like a mold made of something, I could swear that I read not too long ago about someone somewhere who provides a service making molds of objects that you send to them. Sorry to have no details about this...perhaps this will ring a bell someone else in the forums?

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SShirley    9

We are looking for a substitute for plaster for making press molds. Anyone ever try cement without adding the sand?

 

 

Donna,

I have had good luck making slump forms out of mdf board (do you have that in Panama?).

Clay releases from it very well. You might be able to carve simple designs into it for press forms.

Sylvia

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Marcia Selsor    1,301

If you look at a copy of "The Potters of Atcalan" by Louana Lackey, there are photos and descriptions of Mexican potters using clay press molds for their famous Toad pots.

I still think this is the most simple solution to your dilemma. If you bisque fire the molds, they will last a long time and can be cleaned.

 

Marcia

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pipingcat    0

You can use bisqued forms. It has been done in ancient Central Asia and Central American.

Marcia

 

 

 

Marcia, when using bisque for a tile mold, wouldn't you need to add in the shrinkage % of the clay twice when making the form? First, to accommodate shrinkage from mold to glazed product and then to accommodate the shrinkage of the mold itself when bisqued?

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Marcia Selsor    1,301

You can use bisqued forms. It has been done in ancient Central Asia and Central American.

Marcia

 

 

 

Marcia, when using bisque for a tile mold, wouldn't you need to add in the shrinkage % of the clay twice when making the form? First, to accommodate shrinkage from mold to glazed product and then to accommodate the shrinkage of the mold itself when bisqued?

 

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Marcia Selsor    1,301

yes. SO do shrinkage tests and make the mold that much larger. This process has been used for ages. You'd have to do at least one shrinkage test for plaster anyway or whatever else you might use.

Marcia

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DAY    8

We are looking for a substitute for plaster for making press molds. Anyone ever try cement without adding the sand?

 

 

Here in Pennsylvania I used "Gauging Plaster", sold at builders supply stores. It is used to plaster walls, run detail and cornice molding, etc. Cheaper than plaster of Paris, and much more available. Comes in quick set and regular.

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