Making Concrete Rocks
Large rocks set into an landscape give a natural, rustic look to the surroundings. However, the cost and difficulty of moving rocks and boulders into position is often more trouble than it is worth. Luckily, crafty DIYers have an alternative: making your own rocks out of concrete. When finished, the concrete rocks look as if they are natural; since they are constructed in their final location, once they are dry, no additional moving is required. Does this Spark an idea?
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Things You'll Need
- Safety glasses
- Work gloves
- Respirator
- Wheelbarrow
- 10 Portland cement
- Fine sand
- Silica fume
- Fly ash
- Glass fibers
- Water
- Shovel
- Plywood
- Plastic tarps
- Foam
- Serrated knife
- Wire stakes or clothes hanger
- Bucket
- Trowel
- Garden hose
Instructions
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1
Put on safety glasses, work gloves and a respirator before beginning to mix the concrete solution.
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2
Pour all of the following ingredients into a wheelbarrow: one bag of number 10 Portland cement, 15 gallons sand, 6 1/4 gallons un-densified silica fume, 1 1/4 gallons fly ash and one handful of glass fibers. Mix all of the ingredients with a shovel until they are well combined.
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3
Add water 1/2 gallon at a time and mix well with the shovel until the mixture is entirely wet and has the consistency of oatmeal.
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4
Lay a piece of plywood on the ground where you want to install the rock. The plywood should be as least as large as the base of the stone that you want to create. Arrange plastic tarps over the ground around the plywood to catch excess concrete.
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5
Lay large blocks of foam on top of the plywood and cut them into a general round rock shape with a serrated knife.
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Insert metal stakes, or an untwisted metal clothes hanger, through the multiple layers of foam to hold them together.
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Pick up a handful of the concrete mixture and apply it to the bottom of the foam near the base, slapping it firmly into place. Apply additional concrete around the bottom perimeter of the foam until it creates a layer 2 to 4 inches high.
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8
Return to your starting position and apply a 2- to 4-inch layer of concrete to the foam located above the previously applied concrete. Continue this process all the way to the top until all of the foam is covered.
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9
Dip a trowel into a bucket of water and use the back of it to smooth the outside of the concrete into the desired stone shape. Work from the bottom of the concrete upward for best results.
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10
Rinse the trowel and use it to carve out some areas of the concrete to create natural-looking, jagged rock edges.
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Water the rock with a light spray of water three times per day for three days.
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Allow it to cure for 30 days before attempting to move it.
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Tips & Warnings
If the concrete starts to set before you are finished molding it into a rock form, spray it with a fine mist of water from a garden hose.
