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Making Rocks for Your Model Railroad

modeling artificial rocks

There are lots of ways to make rocks for your railroad layout or diorama...

  • Hydrocal and rubber rock molds - This is one of my favorite methods. Start by purchasing one of the many varieties of rock molds that are available commercially. [Or you can even make your own rubber molds if you wish, using multiple layers of liquid rubber latex (with cheesecloth sandwiched in between) onto the surface of a real rock that you want to copy.]  Then mix Hydrocal and water till you get just the right consistency of cream soup. Try to avoid bubbles as much as possible.  (You can add some brown or gray acrylic paint at this point if you know you want your rocks to have a base color upon which you can paint other colors later.)  Spray the inside of the rubber mold with a mixture of a few drops of dishwashing soap diluted with water, which will make it easier to remove the rock from the mold after it has dried.  Pour the Hydrocal mixture into the mold right up to the top of the mold and let it sit overnight to dry. Remove the rock the next day and incorporate it into your layout landscape by adding a small amount of Hydrocal around the edges of the rock.  If you have any unwanted cracks in the rock, you can fill them in with the Hydrocal. 

This rock face was made with a combination of rubber rock molds and Sculptamold...

Model Railroad Rock Face with Deer

  • Aluminum Foil - I have used wrinkled tin foil as a mold for making rocks, especially when I wanted to make a long rock wall.  Make sure the foil is wrinkled up enough that it will create detailed crevices in the rock surface. Support the foil using a small cardboard box so the mold doesn't fall flat on your worktable when you add the Hydrocal. You can use whatever material you want (I used damp sand) under the foil to make it curved or straight depending on where you want to put the rock on your landscape. Pour the Hydrocal into your tin foil mold and let it dry. You can either let it dry all the way, or you can just let it thicken and then apply it to your landscape, tin foil and all, so that you can gently mold it into the contour of your landscape.  Then let it dry overnight. When you take the foil off the next day, you will have a nicely detailed rock wall that follows the curves of your landscape.
This rock wall was made using tin foil as a mold...

 

  • Sculptamold- This is a great product for making rock walls and cliffs, though not so good for making rock molds, because it lacks the detail that Hydrocal has. However, if you want a rock wall or cliff, You can mix up a batch of Sculptamold to about the consistency of oatmeal and apply it to your surface with a putty knife.  Create irregularities and crevices in the rock as you go to make it more realistic.  You can also scratch out more details in the surface after it has dried.

 

This cliff was made with Sculptamold...

Rock cliff made with Sculptamold

  • Ready Made Rocks - If you don't want to put up with all that water-and-plaster mess, there is another option thanks to the folks at Woodland Scenics.  They have recently made a product called Ready Rocks, which look very realistic and can be added to your layout right out of the box.  Just add some vegetation around the edges and you're done! The product comes in 4 different types - outcroppings, surface rocks, rock faces (which can be fitted together to make rock walls) and creek bed rocks. 

If you want to see more on this topic, go to the "Making Rocks" page on the Building Your Model Railroad website.

Next we'll be talking about how to paint your rocks.  Stay tuned!