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need recipe for making molds


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#1 Saoirse

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Posted 17 August 2012 - 10:44 AM

Good morniing!

I am in need of a way to make molds by mixing some material, such as white cement and gesso...I am not sure if anything else is needed or if I am using the right terms.
I live in South America and things are not labeled the same.

If anyone knows a recipe for making these plaster "type" molds for ceramic tiles, I would really appreciate your help.

Thank you!
Nancy

#2 neilestrick

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Posted 17 August 2012 - 10:47 AM

Is there some reason you don't want to use plaster?
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#3 Saoirse

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Posted 17 August 2012 - 11:53 AM

Is there some reason you don't want to use plaster?


Honestly, because I have lived here for 4 years and learned to use Spaniish instead of English for such things, I am confused about what I want to use.

Plaster is yeso here. Is a construction type plaster sufficient to use for molds? If that is the case I have some...

I bought some potter's plaster a year ago or so in a big bag, but it is not usable and has gone up to 60.00 a bag, pretty costly for me and especially when it goes bad if you don't use it up quickly.

Just wondering if there are different options to cut down the cost. Hope you understand.

Thank you.



#4 neilestrick

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Posted 17 August 2012 - 12:11 PM

As far as I know, plaster is the best thing for molds. There are different types of plaster, although #1 Pottery Plaster is the most commonly used type and works very well. If you're going to be making molds with a tile press or doing long runs, you may want to try a harder plaster like HydroStone or HydroCal.
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#5 Saoirse

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Posted 17 August 2012 - 12:24 PM

As far as I know, plaster is the best thing for molds. There are different types of plaster, although #1 Pottery Plaster is the most commonly used type and works very well. If you're going to be making molds with a tile press or doing long runs, you may want to try a harder plaster like HydroStone or HydroCal.


Thank you for your help...I did some reading on this site and I am understanding it better...perhaps our molds have not cured as of yet and it will be harder as it cures.

Appreciate your knowledge.

Nancy

#6 neilestrick

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Posted 17 August 2012 - 12:55 PM

Your molds should set up hard in 1/2 hour or less. It will take them several days to dry completely, though. Putting them in front of a fan will help. Never use heat to dry them. Also make sure you are using the correct amount of water in the mix. #1 Pottery Plaster needs 7 parts water to 10 parts plaster by weight.
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#7 Christine

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Posted 17 August 2012 - 01:48 PM

I remember some articles in CAD last year (http://ceramicartsda...-ceramic-molds/) which might be of interest. I use plaster of paris, which I think translates as "yeso blanco"

Hope this helps
Christine

#8 Saoirse

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Posted 17 August 2012 - 09:20 PM

Your molds should set up hard in 1/2 hour or less. It will take them several days to dry completely, though. Putting them in front of a fan will help. Never use heat to dry them. Also make sure you are using the correct amount of water in the mix. #1 Pottery Plaster needs 7 parts water to 10 parts plaster by weight.


Thank you for your help with this...I think the plaster is different here as when I scratch the mold, it scratches off and I don't think the potter's plaster did. I will research a bit more to
find out if there is another type available. Someone suggested mixing in some white cement...hmmm...not sure about that but, may try it.


Thanks again.

#9 Saoirse

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Posted 17 August 2012 - 09:21 PM

I remember some articles in CAD last year (http://ceramicartsda...-ceramic-molds/) which might be of interest. I use plaster of paris, which I think translates as "yeso blanco"

Hope this helps
Christine


Thank you for the info...I'll let you know. :-)

#10 Lucille Oka

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Posted 17 August 2012 - 09:45 PM

Saoirse,

Do not use Plaster of Paris for molds. It is much too soft.

If you still have that bag of #1 pottery plaster take off some of the top and take a look in the center of the bag and see if it is usable; take some out and test it; if it sets and heats up you can use it.
I had a 50lb bag of #1 stored in a kitchen, in a large plastic garbage bag for over a year and it was fine. I made a wedging surface from it.
If you decide to buy some #1 pottery plaster be sure to store it in plastic bags that can be closed securely.
There really isn't much of a substitute for plaster when it comes to moldmaking; Hydrocal white or #1 pottery plasters are the best.

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#11 INYA

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Posted 18 August 2012 - 02:30 AM

We are using Modelling plaster (Modellgips) from a big construction material supplier - Rigips, you could check in big stores with constuction material.
It is quite ok, not grainy and cures in half an hour. Picks up the details fine and it is ok for hand pouring (not sure about the machine). Costs around 4,5 usd/ 5kg. Small bags are great to carry around (I have a weak back) and you dont worry about plaster going bad, + you can buy exactly as much as you need.

But anyway, plaster should not go bad in one year! We are working with plaster (for other things) for 10 years now and none has gone bad. But there were one or two bags which were bad from the beginning.
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#12 clayshapes

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Posted 18 August 2012 - 05:53 AM

I'm planning on making some molds next weekend. Is the plaster I can buy at a place like Home Depot okay for this task - or do I have to use Potter's Plaster? I assume the plaster at Home Depot is for "mudding" drywall. Would it behave the same as potter's plaster? What is the difference?

#13 WillowTreePottery

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Posted 18 August 2012 - 07:48 AM

I'm planning on making some molds next weekend. Is the plaster I can buy at a place like Home Depot okay for this task - or do I have to use Potter's Plaster? I assume the plaster at Home Depot is for "mudding" drywall. Would it behave the same as potter's plaster? What is the difference?




I would stick to using #! pottery plaster for the longevity of the molds. Other plasters will end up chipping and pitting as you use them and do not cure the same. I have used dental plaster or Hydrocal in a pinch but still prefer the pottery plaster.



Kathy

#14 clayshapes

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Posted 18 August 2012 - 07:55 AM


I'm planning on making some molds next weekend. Is the plaster I can buy at a place like Home Depot okay for this task - or do I have to use Potter's Plaster? I assume the plaster at Home Depot is for "mudding" drywall. Would it behave the same as potter's plaster? What is the difference?




I would stick to using #! pottery plaster for the longevity of the molds. Other plasters will end up chipping and pitting as you use them and do not cure the same. I have used dental plaster or Hydrocal in a pinch but still prefer the pottery plaster.




Kathy



#15 clayshapes

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Posted 18 August 2012 - 07:55 AM

Gotcha. Thanks for the advice. Going out to get some pottery clay (it's further away than Home Depot -- I was hoping to save some time!)

#16 DAY

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Posted 18 August 2012 - 08:48 AM

I'm planning on making some molds next weekend. Is the plaster I can buy at a place like Home Depot okay for this task - or do I have to use Potter's Plaster? I assume the plaster at Home Depot is for "mudding" drywall. Would it behave the same as potter's plaster? What is the difference?


Do NOT use drywall mud!
If you can't find pottery plaster, try 'gauging' plaster. The "real" construction suppliers (i.e. probably not Lowes/Home Depot) sell it, 50 lb bag, about ten bucks. Comes regular and fast set. I think there is a thread here someplace. or use teh GooglePosted Image

#17 clayshapes

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Posted 18 August 2012 - 09:08 AM

My mistake -- the plaster at Home Depot is gauging plaster, in bags --the "mud" comes in tubs already mixed. But I'm going for pottery plaster. Might buy both kinds and do a "taste test" to see what the difference is in practical terms - side by side. Curious to see if it's really all that different.

#18 Lucille Oka

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Posted 18 August 2012 - 03:30 PM

Take a look at this it is the website for United States Gypsum. It will give descriptions of the different plasters that are used in the ceramic industry. http://www.usg.com/i...l/ceramics.html
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#19 Donna Roes

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Posted 22 August 2012 - 08:45 AM


Is there some reason you don't want to use plaster?


Honestly, because I have lived here for 4 years and learned to use Spaniish instead of English for such things, I am confused about what I want to use.

Plaster is yeso here. Is a construction type plaster sufficient to use for molds? If that is the case I have some...

I bought some potter's plaster a year ago or so in a big bag, but it is not usable and has gone up to 60.00 a bag, pretty costly for me and especially when it goes bad if you don't use it up quickly.

Just wondering if there are different options to cut down the cost. Hope you understand.

Thank you.

We use contractors plaster purchased at a hardware store. We make press molds and this has been working just fine for us. No, it´s not as good as potter´s plaster but it´s what we can get in Panama. Try it and see if it will work for you.

Donna & Ray






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