How to Make Concrete Boulders
Concrete boulders add texture and dimension to landscaping. When it may be too expensive to haul in large boulders to use for landscaping, creating fake rocks may be a cheaper alternative. There are a number of ways to make artificial rock and all end up with a real-looking finished product. Once you master the basic technique of making fake rocks, you can let your imagination help you create concrete boulders sized, colored and shaped exactly the way you want them.
Things You Will Need
- Dust mask or respirator
- Protective eyewear
- Chicken wire
- Wire cutters
- Plastic sheet
- Concrete mixer
- Type 10 Portland cement
- Texture mat
- Texture mat release agent
- Putty knife
- Paint mister
- Water-based paint
Create the forms for your concrete boulders. Use chicken wire or a similar mesh fencing product to create the size and shape you want. Place the form on a plastic-covered piece of plywood if you plan to move the artificial rock after you complete it. If you plan to build the fake rocks in place, consider using old pieces of concrete or piles of smaller rocks as the base of your boulder.
Mix the concrete in a bucket or concrete mixer. Put 3 parts sand and 1 part type 10 Portland cement into the mixer and mix completely. Mix in a little bit of water at a time until a ball of mix stays together in your hand. If dropped from knee level, a handful of concrete should form a round, almost flat circle.
Add concrete one handful at a time around the base of the boulder structure. Use a trowel to work the concrete into the mesh of the fencing but don’t push it more than an inch. Work in 3 to 4 inch rounds until you cover the top of the artificial rock. For best results, cover the form with 1 1/2 to 3 inches of concrete.
Dip your trowel in water. Use the trowel to smooth out air bubbles and rough spots in the concrete. Use the tip of the trowel to create fissure lines and cracks if you want them.
Spray the concrete texture mat with release agent. Lightly spray the release agent on the concrete boulder as well. Press the mat into the surface of the concrete to form the desired texture. Let the entire boulder cure for three or more days before proceeding.
Scrape any rough edges from your concrete boulder with a putty knife. Turn it over to get to sharp edges along the bottom. Wash the dust from the concrete. If you built the artificial rock in place, you can skip this step.
Create spray paint for the paint mister made of 1 part paint and 3 parts water. Practice on a piece of scrap material. Spray the artificial rock. If you are using different shadings, mix different colors and layer them on.
Wear personal protective equipment. This includes gloves, eyewear and a dust mask or respirator.