How to Sand-Cast Fake Rocks

Sand cast fake rocks look more natural when they are irregular.

Wet sand holds a detailed shape well, and you can create or change the mold very quickly. If you have an object you want to duplicate, you can press it into the sand and replicate the design repeatedly, without damaging the original.

This means that you can have what nature will never provide: custom yet identical rocks with a unique design, perfect for creating lining a walkway, decorating a garden or building a small wall.

Things You'll Need

• Dimensional lumber
• Tarp
• Drill
• Screws
• Screwdriver
• Clean sand
• Water
• Wet cement

Instructions

1. Create a box for the sand mold, placing four pieces of dimensional lumber in a square slightly larger than the size of the rock you want to create. You can work on top of a tarp to protect your work surface from the sand rather than build a bottom for your box; it may also be easier to release the mold if there is no bottom.

2. Drill holes in each end so that you can easily insert and remove screws from the sides of the box, to help release the cast rock and sand mold.

3. Moisten the sand with enough water so it holds a shape. Don't add too much water or you'll extend the cure time for your cement.

4. Pack the sand into the box well.

5. Create a pattern in the sand. Remember, the rock will be the reverse of the mold. For instance, if you want to create a rock with your house number, create a mirror image of the address in the sand.

6. Pour the cement into the mold gently. If you add too much force, the sand in the mold can shift.

7. Allow the cement to cure according to the manufacturer's recommendations.

8. Release the rock by either prying it out of the mold, flipping the mold, or, if necessary, opening the box and moving the sand away from the rock.

9. Wash the new fake rock to remove all sand.

Tips & Warnings

• If you prefer not to create a bottom for the box that holds your sand mold, you can build it on a tarp to protect your work surface from the sand.

• Ask your cement supplier for additives to color the cement. Real stone is not uniform in color or texture; stop mixing the additives into your cement before the color is homogeneous.

• You can use smaller rocks or other objects to make patterns into the sand mold or leave them in the mold just as natural rocks contain other materials.

References

• "Concrete from sand molds"; Albert Allison Houghton; 1910
• "Making Art with Sand and Earth"; Gillian Chapman and Pam Robson; 2007
• "Casting for Crafters"; Marie Browning; 2006