Plaster of Paris or Hydrocal

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#21
It looks like the Charcoal color would be the best for hydrocal rock. What colors have you tried or anyone else reading this :)

Plaster of Paris, USG Hydrocal, and gypsum cement are all beta gypsums, with similar characteristics. Alpha gypsums, on the other hand, are much harder and stronger than beta gypsums, and are often referred to as "stones." These are the types of plasters used in dental applications, called "dental-stones," or "die-stones." They're rated in strength from Type III to Type V, with Type V being strongest.



For modeling applications, Type IV is best (Type V is slightly stronger, but costs three times as much). A 25-pound box of Type IV dental-stone can be had for only about $20. Find this locally from a dental laboratory supplier in your area. Their quick setting times and superior strength make them excellent plasters for pouring finely detailed rock-molds. These are the same types of dental-stones sold under the brand, "Merlin's Magic," which offers a variety of dental-stone plasters in model-friendly colors; however, the shipping costs make the product costly. It's much better to buy this locally. If you can't find a dental lab supply nearby, your dentist can order it for you.

Here's the relative strengths of the various plasters, measured in PSI of compressive strength, according to Hirst Arts:

Plaster of Paris: 2,000-5,000 PSI
Hydrocal: 6,000-8,000 PSI
Type IV dental-stones: 12,000-14,000 PSI
Type V die-stones: 18,000 PSI



Plaster of Paris, Hydrocal, Sculptamold, and even Celluclay are all easily colored using Quikrete-brand liquid concrete colorants. They're available from Home Depot in a variety of earthy colors. They're so concentrated, you only need very little colorant to color your rocks. Tempera or latex paints typically require much more material to achieve the same depth of color, and can significantly compromise your plaster's setting strength.
 
#22
Everyone -
Okay, I've read all the comments on this post and I see Hydrocal seems to be the weapon of choice.

So, my question is: Hydrocal VS Sculptamold VS Plaster of Paris or anything else. So far Sculptamold is the only product I've used, mainly 'cause it is easy to find. You have to drill holes in it to put trees in the scenery, and it sounds like Hydrocal is equally hard if not harder. But that's not a big issue. What are your opinions on overall "sculptability" and ease of use in making scenery?
 

Selector

Active Member
#23
Sculptamold, as its name suggests, is the best for covering gaps, shaping around vertical surfaces when blending to a level one, and so on. Hydrocal is best for rock molds and for bridge abutments and such where you want some strength.
 
#25
There is one thing I like about hydrocal that I find very useful. When I'm casting parts and I want to carve details into the object there is a long period the casting is green. This is when the casting is still soft enough (moist) to carve in the details without the casting chipping or cracking because it hard.

A thought I had was to try and mix the different items together and see if you can get something that's the best of all. Stays green long to work details, get stone hard when dry, and you can color with pigments or tempera paint powers so you don't get white chips over time.

Dave
 

wombat457

Well-Known Member
Staff member
#26
If you want strength and durability, especially when casting something, use Dental Plaster. Very very hard and made for castings when it comes down to it. Also a lot cheaper than other products for the same or similar amounts.
 
#27
There is one thing I like about hydrocal that I find very useful. When I'm casting parts and I want to carve details into the object there is a long period the casting is green. This is when the casting is still soft enough (moist) to carve in the details without the casting chipping or cracking because it hard.

A thought I had was to try and mix the different items together and see if you can get something that's the best of all. Stays green long to work details, get stone hard when dry, and you can color with pigments or tempera paint powers so you don't get white chips over time.

Dave
Dave - thanks for this information. I've heard several times that Hydrocal stays green for a long time before hardening. Good quality. I don't know about mixing the two products together, but it might be worth a try.
 

wombat457

Well-Known Member
Staff member
#29
Johnny,

I get mine from "Merlin's Magic". Here is the website if your interested in taking a look.

https://merlinsmagicplaster.com/

The one thing I like about this product is that it does dry quickly, very hard and very smoothly. You don't get the pitting that you get with other products.

The only foreseeable downside to using Dental Plaster/Dental Stone is how quickly and how quickly it dries. While it it excellent for molds and castings, it will be harder to sculpt or carve.
 

wombat457

Well-Known Member
Staff member
#31
Thought it might for your purposes other than for castings and molds. It is worth keeping in mind if you are going to use molds and does work far better than anything else I have tried in a mold.

I can't say anything about their molds as I have never used one. It would be interesting to get one and see how it performs just out of curiosities sake.
 
#32
Thought it might for your purposes other than for castings and molds. It is worth keeping in mind if you are going to use molds and does work far better than anything else I have tried in a mold.

I can't say anything about their molds as I have never used one. It would be interesting to get one and see how it performs just out of curiosities sake.
Yeah, I'll keep this info and their website in a file for possible future use. Their molds look kind of small (each piece in the large mold), but small pieces like that might be more flexible to build stuff with.
 



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