# Latex/ plaster info



## Allen H (Feb 13, 2010)

Hey guys, I just answered a private message about latex and plaster questions and I thought it might be helpful to repost.
The question was basicialy "Why am I getting poor results with molding latex in plaster of paris molds, it takes Days to dry?
here is my reply:

You are getting inferior results because you are using inferior products.
In the grand scheme of things latex isint that expensive, buy a gallon of casting latex from monstermakers or Screamline studios. Casting latex is meant for makng casts and the moisture is easily wicked from it (a major aspect of drying). 
The thicker the latex the more it wants to hold on to its moisture. casting latex is meant to air dry so its terrible for use in a mold. Combine that with plaster of paris which isint very pourous and it takes FOREVER to dry. Its almost like you put it back in its plastic tub. The molding latex that comes in the tub is full of fillers, chalk, all kinds of solids to make it thicker, they kill the elasticity also. Think of them like breadcrumbs in meatloaf- meant to hold in the moisture and prevent drying.
While you arent making a mask you still want latex that will dry in a plaster mold, so you want the same effect. 

Now begins my anti plaster of paris tirade. Its garbage. It is formulated to give walls a smooth texture. That smooth (non pourous) surface really slows the rate that the plaster wicks moisture mout of latex. It is also fine for finished pieces (indoor statuary or bisque) because of its surface texture but its also very brittle, so for a mold detail will chip off quickly.
Ultracal 30 is the plaster of choice, it runs about $35 for a 100lb bag, Plaster of Paris runs $7 for a fivelb bag. So ultracal is much cheaper. Ultra cal is pourous and wicks moisture very quickly from latex. baking out the mold makes it go even faster, a thin enough layer will dry almost as soon as its painted on.
I hope this helps you out a bit, but basicially use casting latex and ultracal 30. Using mold latex and plaster of paris is like trying to make applesauce from oranges and beer- its in the apple family cause its fruit, and the beer is mostly water- but you will have very bad applesauce.


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## IMU (Apr 8, 2009)

Yep ... that was me!  

Going to try a better applesauce mix soon ... thanks for the info! 

Now I have to find the Ultracal 30 thats local ...


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## tcarter (Aug 18, 2006)

Allen H said:


> Ultracal 30 is the plaster of choice, it runs about $35 for a 100lb bag, Plaster of Paris runs $7 for a fivelb bag. So ultracal is much cheaper.


Not if you can't get it locally. shipping charges will kill ya. What would happen if you mixed some portland cement into Plaster of Paris to strengthen it?


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## Frighteners Entertainment (Jan 24, 2006)

great info and written out simple, thanks Allen.


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## RoxyBlue (Oct 6, 2008)

Now all we need is that recipe for orange beer applesauce.....


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## Acid PopTart (Oct 29, 2007)

Thanks for the info Allen, I was just reading about the performance of Ultracal. Guess I was lucky to find it locally at a clay supply company in Columbus, OH.


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