Concrete spheres or balls are a nice and attractive addition to any garden or landscape. The round geometrical shape is different from most other shapes found in gardens and parks, which are generally dominated by trees and shrubs. Most people may wonder how a concrete sphere can be made. It may look like it's a difficult task, but making a concrete sphere is easy if you know the trick.
Cut a 3-inch hole in the top of the rubber ball and pour vegetable oil in the ball. Turn the ball around so that all surfaces inside the ball are coated. Lay the ball on a bed of sand, positioned with the hole at the top. Let the ball sink into the sand by about a third of its height to ensure that it will not get deformed once concrete is poured in.
Mix enough concrete to fill up 1/4 the size of the basketball and pour the mixture into the ball. Measure the height of the basketball and add 4 inches to your measurement. Cut the steel bar according to your measurement and bend the tip into an "L" by about an inch with a bench vise.
Insert the steel bar into the hole. Let it stand upright, then loop six inches of masking tape around the bar at the ball opening and attach the tape to the ball to fasten the steel bar. Attach two more tapes around the steel bar to ensure that it will stay in place. Allow the concrete to dry for a day.
Remove the masking tape and pour enough concrete into the ball to reach to about half its height. Let the concrete dry for another day, then mix some more concrete and fill the ball all the way to the opening. Allow the concrete to dry for three more days.
Cut the rubber ball around with a utility knife and peel it off with a pair of pliers. Sand the concrete sphere with 100 grit sandpaper to make the surface smooth. Cut off the protruding steel bar with a hack saw. You can retain the steel bar if you want to use it as anchor.