I have tried both. To me plaster of paris is easier to work with and cheaper. However I’ve heard comments that it is to heavy. Unless you have a portable layout, I don’t see where weight would be a problem unless I’m overlooking something…comments?
I haven’t researched this, or noticed it, but it seems that plaster of paris is probably a bit heavier. It might add up over many castings applied to a significant layout, but I’d bet it doesn’t add up to more than maybe five or six pounds once it is dry and in place on most layouts.
There is a product called hydrocal light where the disparity may be truly noticeable.
Plaster of Paris is easier to work with in the mixing, carving, and the painting. Hydrocal doesn’t take paint easily. It would do so after priming.
-Crandell
It is true that Hydrocal requires priming before painting, but it is excellent for places that get a lot of hands-on use and for water proof base for rivers. It is extremely non-chip, and molds well. Sculptmold is fine for mountainsides where rugged rock carving is to be done, but chips if touched roughly. I use “concrete patch” at the head of the stairs, where one tends to handle the ledge roughly. Hydrocal is my preference for molded outcrops, since it is tough. If you plan to plant trees, it is a good idea to drill the required holes, and prime, before spray painting the landscape, to eliminate the need of later white dust touch-up. Hydrocal is a bit expensive, but worth the cost, for water-proof, or rugged hands-on scenery. Bob Hahn
I find Hydrocal is better for making rock castings. Plaster of Paris (Hilton?) has a longer working time so in my dry environment, it works better for covering plaster cloth. I prime neither when painting.
Micro Mark has a very attractively priced Hydrocal offering (compared with WS).
I find that hydrocal is just a little lighter than plaster, but doesn’t give you a really long ‘working’ time, at least in my California Basement (garage) layout. But it is awfully good for rock castings. Light and strong.
Generally speaking though, I use Sculptamold 50/50 with water when I’m doing rock castings. It’s a slower method and takes longer to set up, but I like the results. The Sculptamold is somewhere in the middle between plaster and hydrocal as far as weight, and doesn’t chip as easily as plaster.
But all three DEFINITELY have their uses.
Tom
I have used both and I color my rock castings with diluted acrylics. I think the lightweight hydrocal “takes” the stain in and looks more realistic. Just my opinion…Tim
I can’t give you statistics on this, but plaster of paris is a lot heavier than Hydrocal.
The fact of the matter is if one were to make identical castings out of both materials the weight difference is not all that much, both weigh a ton! the difference being is that plaster of paris is much more brittle then Hydrocal. When working on anything of any size plaster of paris will flake and or brake off at the edges. Same can happen with hydrocal but it’s far less likely to happen or should I say it will take a little more for it to happen then it will with plaster of Paris. Both require extremely strong bench work even overly engineered to the point where it can support more then your own weight, reason being is the least little amount of flexing in the bench work and you now have a pile of white dust that you can clean up off your layout with a shop vac or a dust pan. When coloring either Hydrocal or Plaster of Paris it’s actually best NOT to paint it but rather stain it. Strictly my O/P as some doe paint hydrocal to seal it first. It’s natural tendency is to suck up stains or washes etc. like a sponge. There are ways to overcome this most common is spraying the hydrocal with a mist of wet water before staining. This helps slow down the absorption process. When you stain things like hydrocal walls tunnel portals etc. you get far greater detail then you would by painting. The pictures below are of a Hydrocal High Arched PRR prototype stone viaduct that I’ve been working on the past week or so. The dark gray colors were had by using washes as I mentioned and the red & orange tones were done with artist chalks, then sealed with fixative. Sorry for the poor picture quality but the reddish color of Pa. Stone is not really well represented by my poor photography.
Tom, I say… both… and neither… lol.
Ah to make this very short. I use ‘Dental Plaster’ its cheaper… and I believe the same as Hydrocal. Densite is the name.
But in short… using the hyrdrocal/dental plaster. Its stronger. Way stronger. I pour less… and use a clothstrip on the back for added strength. I use less plaster… pour a thinner mold… and is light… but strong.
Example: I had poured a tunnel portal using the dental plaster. Left it sitting on the edge of my work table. Well, the thing fell off the table and landed on the tile floor. “CLANK” was the sound, a high pitch clank. I picked it up off the floor… looked for chips… cracks… nothing. Then I knew… I’ll never ever use anthing else.
Now all I do is, just paint a 1/4 thickness of plaster… lay in a cloth strip and done.
Not the best photo… but study this sheet… I believe it helps.
I have poured large faces of rocks… using less and less dental plaster.
Of course this is the backside… but its to show you how thin. Good luck.
Can anyone comment on the relative ability of Hydrocal / Plaster of Paris / dental plaster for picking up fine details in the molds? I suppose this would be determined by the size of the dry grains. I have some really nice molds which give great results with Hydrocal.
I’ve also used Bragdon Foam with a Bragdon mold. This gave very nice results, too. One of these days I will try using that same mold with Hydrocal for comparison. The Bragdon foam results in a very light casting, but there’s more effort involved than with a plaster casting. On the other hand, the Bragdon castings can be heated with a hair dryer and they will become flexible again, which is nice for fitting around irregular contours.
Mister Beasley… “Can anyone comment on the relative ability of Hydrocal / Plaster of Paris / dental plaster for picking up fine details in the molds?” I also agree with you on the size of the grains in the plaster and would only reply… “You think a Dentists wants a grainy ‘impression’ of someone’s teeth”?
But in answer to your question… I can only tell you what I know… and what I do.
I do have the Bragdon molds…
’
with a ruler to see the actual size.
and the numbers and prices… $15… $18 and $25.
‘Surface Tension’ yes… that is what is keeping the plaster really getting into and adhering to the mold. Even though your plaster mix has been mixed correctly with no bubbles… you can and will still get an impartial filling of the cracks and detail.
I have read of some people treating the mold for a better ‘release’ of the casting out of the mold… but I really frown on it. I dont’ think that is my approach. Besides… you might have a ‘residue’ of ‘Pam’ or God whatever keeping the paint from really adhering to the casting.
I truly believe that all you have to do is ‘wet’ your mold down. Then really dry it. Smack it on the table. Get all the moisture you can see off the mold. What has taken place… you have removed the ’