How to Make Your Own Concrete Rocks for a Fireplace

Make Molds

• 1

  Put on thick work gloves.

• 2

  Place the rocks into a bucket and coat with 1 to 2 cups of cooking oil. Lift the bucket and shake it to make sure the rocks are coated evenly.

• 3

  Space out the sample rocks on a flat surface leaving 1 inch between each rock. Use a rag to spread the oil to any dry spots.

• 4

  Form a 4-inch thick slab of clay that is longer and wider than the surface area taken up by the rocks.

• 5

  Move the rocks on top of the clay slab. Press each rock down into the clay slab to leave an impression that is 1-inch to 2-inches deep.

• 6

  Transfer the rocks to the bucket.

• 7

  Cover the clay with a plastic tarp. Allow the clay mold to harden until it is bone dry and white.

Cast Rocks

• 8

  Cut a square of chicken wire for each rock cavity. Cut the wire so that it follows the shape of the stone with a 1/2 inch overhang.

• 9

  Mix the concrete with the water to reach a thick consistency. Use the trowel to stir the concrete. Gradually add water until the concrete is thick enough to be peaked, but too thin to cling to the trowel when it is held upside down.

• 10

  Fill each mold cavity. Ensure the concrete fills all of the nooks and crannies without developing air pockets by employing one of the following methods: drop large scoops of concrete mixture into the mold from 1 foot above the cavity, and repeat until the mold is full; or use a paintbrush to apply a thin layer of concrete over the surface of the mold cavity, and then pack scoops of concrete into the mold with the trowel or gloved hands. Use a finishing trowel to smooth the concrete so that it is level with the surface of the clay mold.

• 11

  Lay a piece of chicken wire on top of each rock cavity and press it down in the center so that it dips into the moist concrete. Ensure the chicken wire is about 1 inch below the surface of the concrete. Scoop 1/8 cup to 1/4 cup concrete on top of the center of the chicken wire.

• 12

  Allow the concrete to set for 2 days. Use a trowel to lift the edges of each concrete piece out of the clay mold. Break apart the mold if necessary.

• 13

  Lay the concrete rocks on a plastic tarp in a cool place out of direct sun. Spritz the concrete with water and cover with another plastic tarp. Cure the concrete in this position for 10 to 14 days. Reapply moisture every two to three days during curing.

• 14

  Paint each stone with one to two coats of concrete paint or concrete sealer. Use a rag to apply the second coat of paint for a mottled finish. Add sand or gravel texturizer to the paint or sealer to make the surface of the stones rough.