How to Make Backyard Rocks Out of Cement

Building the Form

• 1

  Make the bulk of the size of your rock from foam. This will be covered with cement at a thickness of 2 to 3 inches and will make an artificial rock that feels and looks very real while being much lighter than real stone.

• 2

  Trim the foam block to resemble a rock. This will depend on the size you want your rock to be. Let your imagination guide you in the step.

• 3

  Wrap the foam in chicken wire and a steel reinforcement mesh so that the wet cement will have something to cling to on vertical surfaces.

Mixing the Cement

• 4

  Mix the cement in a bucket by hand or with a point trowel. Alternately, mix it in a wheel barrow with a pointed shovel or on a piece of plywood with a square head shovel. Finally, if you have access to one, mix the cement in a cement mixer.

• 5

  Mix 3 parts fine grade sand with 1 part type 1 (also known as type 10) Portland cement.

• 6

  Add enough water to form a thick paste, and mix a very, very long time before using. If your muscles are not burning, you have not mixed it enough

• 7

  Apply cement to the foam. Keep the thickness at 2 to 3 inches.

Finishing the Rock

• 8

  Sculpt the cement using a point trowel. Observe natural rocks and try to copy their looks. Sculpting rock is a very marketable skill and takes practice to achieve consistent results.

• 9

  Texture the cement using a sea sponge to create a pock-marked, weathered effect. Texture mat imprints from real stones will drastically increase the cosmetic appearance of your rock. Nothing looks more like real stone than an imprint made directly from a real stone.

• 10

  Cure the cement. Cement takes a full month to cure, and is about 75 percent cured after the first week. If the rock is left to sit in direct sunlight during the curing stage, hairline cracking can become a problem. Soak with water often to minimize hairline cracking and maximize proper curing.

• 11

  Scrape the cement. Wait a minimum of 3 full days of curing before commencing this stage. Using a fine-grit scraping stone, grind the entirety of your artificial rock to remove rough edges. When finished, your rock should be smooth, just like real stone.

• 12

  Wash the cement. Wash the rock thoroughly before proceeding to add color. Use a stiff (but not wire) brush to clean the cement dust out of all the nooks and crannies. Dry completely before coloring.

• 13

  Paint the cement using spray bottles and water-based paints. Mist multiple layers of complimentary colors over and over again to create a deep and realistic rock color. Inspect real stones closely to learn which colors produce which effect. Common colors of real rock include blue, green, red, orange, yellow and brown.

• 14

  Seal the cement using water-based cement sealant. Apply three layers, allowing time to dry completely between. Reapply once yearly using a spray bottle to retain color.