Pouring, Shaping, Installing, Coloring, and Detailing Rock Castings

I received several emails regarding my rock casting techniques which I really appreciate. So I am returning the appreciation by detailing step by step how I get my rock castings to look realistic.

1. Pouring the Casting – First I pick out a mold that will fit the space I am working on. Molds by the way can be purchased or made like I did. I made dozens of all different types of rocks with liquid rubber latex that is applied in several layers to build the thickness.


The key is the first layer as it holds all the detail so I make sure to brush the latex in every groove and hole on the rocks surface. The remaining layers build the thickness so the mold does not tear when removing it. Now I can create hundreds of castings. Make sure if you purchase molds that you get several as you do not want your rocks to look repetitive. I use dental plaster for my moldings as it is super fine, starts to setup in 5 minutes and can be installed on the layout in 30 minutes. Full cure time is about 24 hours. Dental plaster is very hard to find but if you know a dentist you shouldn’t have any problems. I am sure some of the fine molding plasters out there may do a similar job. I start by mixing just enough plaster to do the mold as I only have 5 minutes to work with it. I wet the mold and pour in some plaster and tap it with a spatula t0 get any air bubbles out and to help it flow into all the detail. I make sure to have enough plaster around the edges as if it is not thick enough, it will chip when I go to remove it or when I am installing it. After I have filled the mold with plaster I leave it to setup but return every 10 minutes to spray it with water as the dental plaster heats up in the curing process. The water keep the plaster from getting brittle.


After about 30-40 minutes I can safely remove the casting from the mold to reveal a perfect replication. This one has obviously been colored as it would come out of the mold stark white.


2. Shaping the Casting – Once I have removed the casting from the mold, it needs to be shaped to fit the space on the layout. All I use is a pair of side cutters to chip off what I need to. Only chip off small amounts at a time as if you try to remove too much at one time it will crack or break. At this time I also clean up the edges of any plaster run off that may have occurred during the molding process.

3. Installing the Casting – I use cardboard strips and wooden strips to support the casting as I install the casting first before any other scenery. I use durabond 90 as an adhesive as it gives me 90 minutes to work it and I make it much thicker than normal so it does not run. I place small amounts of plaster around the back side of the casting to secure it to the cardboard strips. Then comes the boring part. It takes about 24 hours to fully harden. I usually do 1 casting at a time if multiple are involved because it is so much easier working with a hard surface than trying to get two moving pieces to co-operate. Once the casting has fully hardened I go back and apply more plaster around any areas that I can to help secure it better as some of the scenery toweling will be supported by the casting and I want to make sure it does not more when applying toweling or even coloring.


4. Adding Coloring – I do the coloring once all the plater scenery in the area is done as I would not want to wreck the finish with a dropped glob of plaster. I use a fine plaster and dry powder coloring mix like used in zip coloring but I add a little bit of water to create a runny color mixture. I use at least 5-7 colors to create random yet realistic results. First I use a charcoal wash on the whole casting to make it light grey and to take away that bright white plaster look. I make sure to spray the casting first with lots of water. The plaster absorbs water and if this is not done first before applying any coloring than the color will lock in to the plaster and can’t be changed. If the casting is wet than I can apply the color with a brush and if it is too dark I can spray it down to thin it out. This also help to flood colors in the cracks and allows it to build up in the cracks which looks really real. I repeat these steps with each color randomly adding color to my liking. Nature is not perfect so it is really hard to mess up hear. Just make sure the casting is always wet and you can’t go wrong. Usually I start off with the darkest colors of grey, brown and gradually go lighter. I finish with some small amounts of yellow and green to represent moss and and to add character. The finished casting will appear quite dark at first but once all that water dries, it will lighten up. You can always go back and add more color to you liking.

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5. Final Detailing – I finish the casting and area off with some Woodlands Scenic colored turfing, trees, shrubs, field grass, etc… I often add some Woodlands Scenics foliage to my castings to represent vines growing down the side or up from the ground. This is a great way to also hide any imperfection like casting seems or chips. I also put some underbrush in a few cracks to add more dimension and life as when I see rock cliffs in the real world, there always seem to be bushes or even tress growning out the sides. I finish the ground with rock run off. Lots of fine sand like material and some larger rocks in piles looks good too. I add a fine dusting of green and yellow for some grass and the odd piece of wood or junk and then do the ballasting if near the tracks and it is done. Other details such as people, wildlife, trees, etc.. can always be added to suit the scene. I try not to complete a scene in one session as I find that when I come back to continue working on a scene I see something different or have a better idea to make the scene look better.


I hope this information helps to improve your skills and gives you ideas to implement on your layout. I am learning all the time as I find this hobby a continual learning experience. Some good, some bad but always fun.


4 responses to “Pouring, Shaping, Installing, Coloring, and Detailing Rock Castings

  1. Very good!

    I had a bunch of castings on my old layout, but none so far on the BS&T. I used tin foil molds for a lot of them. It worked quite well and the mold could be quite large. I have a large mountain project coming up around the mine in Derwin’s Drop. I’ll try some of your colouring ideas there for sure!



    Thanks for you comments. I am glad that you got something out of this post. I will keep visiting your blog for updates.
    Thanks again

  2. Nice post, thanks for sharing the details. Your rocks look great. I definitely agree with the learning experience comment, it has been a life long learning experience!

    Thanks for your comments. I will continue to do updates as things progress. This weekend I am starting a pony tresel bridge. I will do a post once it is done.
    Thanks again

  3. Thanks for the great “How To”. i am at the stage of making rocks for my layout. Perfect timing and good ideas. 🙂

    Tom Mann

    Thanks for your great comments. I hope my post helps. You will have to email some image once you are done. I would love to see them.

    Thanks again

  4. Great How-to I read though it twice actually.

    Thanks for your great comments. I will continue to provide quality posts and will respond to as many email requests as possible.
    Just doing my part to help make railroading more fun and encourage more people to take up the hobby.
    Thanks again and have a great day.

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