casting rocks


BigE

BigE

Active Member
I plan on casting some rock face stuff for a mountain.
My question is what do you all use for your casting work?

I'm thinking to just get a bag of powder plaster mix from the local big-box store would be fine.
I see no need for hydrocal or dental plaster or anything fancy.

For the mountain itself, I already have on hand a couple rolls of WS plaster cloth and a couple bags of sculptamold.
E.
 
I used Plaster of Paris, I guess what you are suggesting is quite similar. What doesn't work too well for me was that crack filler that's used with the tape for hiding seams when installing drywall. However I did find that stuff along with support material (gauze in my case) just great for a base material after it dried overnight.

Willis
 
Weight plays a huge factor in plaster. Depending upon what is supporting your rocks, you may have to go with Hydrocal. I myself used Plaster of Paris because of convenience. I also added reinforcement to the sub structure to deal with the added weight. If you keep your castings thin, it won't be a problem; then of course you run the risk of breaking castings.

For shaping, I used plaster bandages in 2-3 layers. These are quick sturdy and durable. In areas where the gauze was thinly coated, I added patching plaster. The sub-base is woven cardboard in most areas, stapled with at least two staples at all joints. Some are reinforced with hot glue.
 
Red Oak & Western said:
OUCH!! I pay $24.00 for a 50lb. bag of Hydrocal at the local molding supply house. Check around. If you can't find Hydrocal at a local building supply (not Lowe's or Home Depot), masonry, or molding supply house, use plaster of paris.
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That's where I got my hydrocal, at a company that specializes with masonry products. Most people at Home Depot or Lowes probably don't have a clue what hydrocal is. Living in the south, especially in your area I think you could find some. With all of the ornate buildings in the south, I would think that it should be available. Another thing that it is very good at is resisting moisture.
 
I use reglar Plaster of Paris and tin foil molds. Keep the plaster on the thinner side to EASE in the breaking process. Breaking the peices up helps to create a more raandom look to your cliffs.

NOW, with that being said, the rough pattern the tin foil creates was perfect for the type of rock face that I was creating. You can get specific molds for specific types of rock formation, but for thee money, tin foil works great! Lay it on the mountain side (you're making that with the plastercloth, right?) with some extra plaster or crack filler, let it dry in place and paint and ground cover away.

This is what I use:
http://www.acehardware.com/product/index.jsp?productId=1381705
 
ERIC I use Plaster of Paris in my rock molds. Plaster of Paris is more porous than hydrocal and lends itself better to color washes, if that is the way you are going to go. I build all my mountain shells out of hydrocal which gives me a solid base to apply the rock molds to. Are you going to make your own molds? This is pretty easy, a lot cheaper than buying them. This is an old process which is time proven.

Cheers
Mel
 
Plaster of Paris (Lite) is all I use on my layout for forming the terrain and mountains/rock faces. It is quick, cheap, pliable, quick drying and light when dry. Works very well for me.
 
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Just read exactly what you asked - Casting Rocks

Woodlands has some fairly decent Rock Molds that I also use (from time to time) that might be useful if all you want is the rocks themselves. For them I use Dental Plaster and attach them to the PoP terrain, mountain.

As much as I hate to admit this, being Woodlands, they are pretty realistic looking when painted up as well.
 
I've tried both hydrocal and POP and POP set up nicer, carved nicer, and was stronger. The only downside is it is heavier, but that could be a plus. Takes paint and washes great too.
 
Okay, old thread, blah, blah . . .

I see that everyone uses either plaster of Paris or Hydrocal. I'm not opposed to using either except for the fact that I have a few hundred pounds of Westpac Fast Set 20 (20-minute patching compound) sitting around. It's a dry white powder used for making patching compound. I was wondering if it's an okay substitute for these other materials, so I did a Google search and found this post on an 0-scale forum in a thread located here:

TMACK said:
I use mainly Westpac Fast Set 20 [emphasis added]. I use it on my interior walls on my house, work, etc. It was a pretty easy transition to use it for rock molds and terrain on my layout. I have made hundreds of rock castings with it and had zero problems. I do spray the molds with a water with a few drops of soap solution before casting.

The reason why hot mud is the best way to go is that it is designed for drywallers/plasters to finish a job quickly, it has to lay down smooth, harden quickly, not shrink or crack. 20 min hot mud is the best solution for castings as you can pop the castings out quickly and make a bunch in one day. It is also great for shell work as it hardens quickly. 20 mins is an eternity. They sell it in small boxes (if you want to test it), you can get fast set 90 if you are not sure, but for castings after you get the hang of 20 min, you'll move to the 5 minute hot mud.
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Hydrocal isn't stocked at Home Depot or Lowe's, but a local building supply has it. It's $44 a bag. The bag is 100-pounds. It's the smallest size they carry. I really don't need another 100-pound bag of anything at the house. I was about to run down to Home Depot and pick up a bag of plaster of Paris for $16 then realized I had bought some at one time. When looking for the plaster of Paris (which I never found), I found four 50-pound bags of the Westpac 20-minute product in my outdoor plastic Rubbermaid shed, and it's still powder-dry!
 
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Okay, forget about using Westpac patching compound. It's either too hard to mix the right amount of water (for strength), or just isn't very strong. I looked up a local dental supplier where I live and bought a 25-pound box of white dental stone plaster for $22. It's the casting plaster used by dentists. I didn't pop for the Type IV, but just bought a box of "normal" dental stone. Whatever it is, it's going to be a lot better for casting rocks than patching compound.
 
There are many ways to cast rocks, or should I say rock faces. Basically, you start with hard shell scenery and get that up and set well. Then either make your own rubber molds, or buy them and mix up Hyrdocal, pour into molds, and then using more hydrocal, "glue" them to the hard shell. Be sure to blend your casting edges into the surface that they are attached to with more of the same stuff ..

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Like this -- this is how i did it. now to apply the castings to the layout ...

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Here you see the many rock castings glued to one side of the river. On the other side is Styrofoam for a bank. Note is is many small pieces and not all turned the same way. Vary the way the things are set into place ...

Now to finish off that surface ...

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After giving it a couple of day to set and really harden down, it is time to finish off the area. Mix more hydrocal, put in rubber gloves, surgical type and now dig into your soupy mix and gently work the stuff into and around the castings. Smooth out -- make it look like it has been there forever -- and basically you have finished. there maybe some final trimming and crack fill in when the whole thing has set, but that is normal.

Do the same with the other side as well. IF you are adding exposed "real rock" - stones, or any other natural material, this is the time to embed than into your scene.

I hope this short tutorial helps ...

The Aerojet
 
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