In our yard we have a concrete angel a concrete St. Francis and an original concrete sculpture of Quannah Parker. As artists we don't believe in cleaning the "patina" off of outside sculptures. Sculptures in cemetaries are not cleaned nor those in sculpture gardens.
It all depends on what is on it that you want to clean off. If you want to clean off moss or lichen, use a small amount of bleach in water with a scrub brushes. If you are trying to clean off paint spatters or some such use tri sodium phosphate and water. This is a powder like substance you mix in water to create a cleaning solution. It's often used to clean brick and concrete!
I clean my concrete angel in the spring. First I rinse her off to get the leaf and dirt build up off. Then I scrub her down with a soft bristle scrub brush and some soapy water (Dawn is good). Then I spray her with Rinse it and Forget it, which keeps her without any growth the rest of the season.
Use Wet and Forget safe for all surfaces
Low pressure wash, or scrub brush with bleach
Try spraying some Super clean on it and watch it turn brown and rinse it off well. You can get it at any auto parts store or walmart.
Use a soft brush and soap (Dawn) and water. Your concrete may be brittle so be careful.
In our yard we have a concrete angel a concrete St. Francis and an original concrete sculpture of Quannah Parker. As artists we don't believe in cleaning the "patina" off of outside sculptures. Sculptures in cemetaries are not cleaned nor those in sculpture gardens.
You could try a pressure washer
It all depends on what is on it that you want to clean off. If you want to clean off moss or lichen, use a small amount of bleach in water with a scrub brushes. If you are trying to clean off paint spatters or some such use tri sodium phosphate and water. This is a powder like substance you mix in water to create a cleaning solution. It's often used to clean brick and concrete!
I clean my concrete angel in the spring. First I rinse her off to get the leaf and dirt build up off. Then I scrub her down with a soft bristle scrub brush and some soapy water (Dawn is good). Then I spray her with Rinse it and Forget it, which keeps her without any growth the rest of the season.