Plaster for mold-making (to cast latex prosthetics) Hydrocal vs. Home Depot?

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detenten

Active Member
I'm not finding a direct answer by Google, so wanted to just ask!

Is there a difference in performance or safety of buying expensive "casting" plasters vs. using the giant bags of stuff from Home Depot?

Most of my uses will be making molds that I use 1-5 times to make latex appliances (klingon forehead ridges is my current project). I'll also be casting a plaster bust of my head in an alginate mold (with plaster bandage mother shell) soon, too.

I ask, because my local art supply store charges a veritable arm and a leg for plaster. I just paid $28.95+tax for 5# of SculptureHouse brand Hydrocal and it didn't come in a solid gold box.
Home Depot sells 25# for $15.

I don't know if I'm an idiot for paying 10x as much, or an idiot for thinking the stuff that's 1/10th the cost is just as good.

I have asked around my artist and hippie-friend circles and oddly can't seem to find anyone who buys anything other than the Home Depot stuff, though I thought for sure New Orleans would have a brick-and-mortar establishment that sells fancy plaster (since shipping would be cheaper if I just pledged my firstborn son to UPS).

Thanks!
 

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Mr Mold Maker

Sr Member
In my experience, I'd say the main difference is in strength.

Hydrocal cures to a very hard stone like surface, where Plaster of Paris stays very soft and almost chalky. You'll also lose detail very quickly with plaster.

For a mold that will cast 5 or 6 pieces? You should be fine.

For a head cast you will absolutely want hydrocal.

If you use plaster for the head cast, expect to rebuild the ears. You will not get the cast out without breaking them to pieces. The moisture in the alginate can also affect the plaster and give you an even chalkier surface, which in turn affects the detail that you can pick up.


You are absolutely getting overcharged though.. hydrocal where I live is $25 for a 50lb bag.
 

detenten

Active Member
Thank you! This is exactly the information I was looking for.

I'll start to search harder for local Hydrocal that isn't highway robbert.
 

detenten

Active Member
You are absolutely getting overcharged though.. hydrocal where I live is $25 for a 50lb bag.
What kind of retailer carries it where you live?
I'm baffled on where to look and my smart aleck friends are giving answers like "Home Depot" and "The Internet..."
 

GotWookiee

Sr Member
RPF PREMIUM MEMBER
You might try construction companies who order USG products like ultracal and hydrocal. They might have extra you can buy.
I usually buy mine from plaster.com, which is run by USG. Best part is the product is shipped in a resealable bucket instead of those paper sacks where you lose half of the plaster scooping it.

Regular plaster of Paris from the hardware store is really chalky in my experience. If you are doing latex slip casting try No. 1 Pottery Plaster.

Ceramic shops are a good place to try for that, and they may have a lead on ultracal or hydracal.
 

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Mr Mold Maker

Sr Member
I am fortunate enough to live about an hour away from a Reynolds Advanced Materials shop, so I get mine from there.

If you have one close they normally don't charge too much for shipping.

If you can try pottery stores, ceramic stores, or hardware stores. Some Home Depots will special order it as well, but you still may get hit with a shipping price.
 

PoopaPapaPalps

Master Member
RPF PREMIUM MEMBER
I get my ultracal from this place.

I'm about 3 hours away from my nearest Reynolds; I'd rather just pay the 10-13 bucks for shipping than drive 6 hours for some silicone. :wacko
 

jsher1010

Active Member
I found Ultracal (and Hydracal) at a local masonry supply. Pricey though.
I found mixing plaster of paris with vinyl concrete patch (both from Home Depot) gave me better results.
The mould was harder and details stayed 'crisp'. The mixture sets up about as fast as just plaster alone.
 

GotWookiee

Sr Member
RPF PREMIUM MEMBER
I found Ultracal (and Hydracal) at a local masonry supply. Pricey though.
I found mixing plaster of paris with vinyl concrete patch (both from Home Depot) gave me better results.
The mould was harder and details stayed 'crisp'. The mixture sets up about as fast as just plaster alone.
What ratio did you mix them?
How long did the plaster mixture take to setup compared to ordinary plaster? How about compared to ultracal?
What did you cast in said mold? If it was ordinary 407 latex how did the cure time compare to ultracal?
 
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jsher1010

Active Member
I made several small moulds for experimenting with ratios. I found 3 parts plaster of paris to 1 part vinyl concrete patch
gave the result I liked most. If you look at the ingredients in Ultracal, it's plaster of paris and portland cement. My measurements
weren't super precise, just '3 scoops of this to 1 scoop of that'. The ingredients were mixed well together dry then add water like
plaster or Ultracal. Plaster, alone, sets up faster than concrete alone, but when it was mixed together, mixture sets up about as fast as plaster.
Ultracal was similar. I cast latex in it with no problems. I also cast thinned silicone caulk in it with no problems. When casting the silicone
I brushed in liquid dish soap as a release and the cured casting released very easy.
 

paulblopez

New Member
if ur makng prosthetic neither would work you would need either ultracal 30 or 1630 because would need to be baked those cant with stand the heat
 

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PoopaPapaPalps

Master Member
RPF PREMIUM MEMBER
If it's just liquid latex, I found out not too long ago that Party City has them on shelves almost all year round. Since finding that out, I've never bought Latex online.:lol
 

JERRY

New Member
Ultracal is a mix of plaster of paris and ordinary portland cement. see page two of the attached MSDS. It will vary from supplier to supplier but typically its 90:10 Plaster of paris:OPC

http://www.fibertek.ca/MSDS Sheets/Fiber-tek PDF/Ultracal30.pdf

I have done a few molds of varying sizes glove - head - torso scultps with a homemade mix without any issues. just be careful of dust from the products on mixing.
 

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