How to Make Rubber Molds to Make Synthetic Rock

Natural rock formations like this one can be emulated in model building by creating a latex mold.

If you tour hobby shops, you are likely to find some very interesting but very expensive molds for pouring plaster rocks for use in dioramas, vignettes and model railroading. However, you can make your own unique rock faces and stony projections with latex molding and a few household items. The process is very simple, reasonably clean and very rewarding for the hobbyist.

Difficulty:

Easy

Instructions

Things You'll Need

• Rocks with interesting details
• Dish soap
• Hot water
• Old toothbrush
• Sheet of cardboard
• Liquid latex
• 1 inch paint brush
• Hairdryer or heat gun
• Cheesecloth
• Toothpick

1. Locate interesting rocks that have pronounced features that you want to use as molds.

2. Scrub your rocks using an old toothbrush with hot water and dish soap thoroughly; rinse and allow to dry. All chips, dirt, and debris should be cleared from the surface before proceeding.

3. Place a single rock on a sheet of cardboard and apply a single coat of liquid latex rubber with a 1 inch brush, making sure to cover all areas of the upper surface. Do not cover the bottom that is resting on the cardboard, though some spillover is not a problem.

4. Allow to dry until the top is no longer liquid. You can speed up the process by using a hairdryer or heat gun, but don't get too close to the latex or it will melt away as it dries.

5. Continue to add layers of latex and allowing the layers to dry until you have repeated the steps 6 to 10 times.

6. Apply a layer of cheese cloth or thin wire mesh for added strength (See Reference 1).

7. Re-coat the rock over the cheesecloth in several more layers until the cloth is no longer visible, allowing each layer to dry before proceeding to the next.

8. Allow the final layer to cure for 24 hours.

9. Peel off the latex mold. Gently use a toothpick to lift under the mold to start the process.

Tips & Warnings

• Most modern latex has little to no odor, but it is important to work in a well-ventilated area to keep fumes down.

References

• Model Train: Rubber Mold