Things You'll Need
Thick rubber gloves
Phosphoric acid cleaner
Oil-based penetrating stain
Soft cotton rags
Cast stone is created from a mixture of cement, water, sand and other materials to create a substance that can be molded into various shapes to resemble natural stone. Fireplace mantels created from cast stone are often much less expensive than those created from marble, granite or other types of stone. You can change the color of your cast-stone fireplace by applying a penetrating stain.
Clean the cast stone with a phosphoric acid cleaner designed for use on masonry. Generally, you will mix one part of the phosphoric acid cleaner with 15 parts water and apply the mixture to the cast stone with a mop or brush.
Rinse the cleaner away after approximately five minutes with clean water to remove all traces of the cleaner.
Apply an oil-based penetrating stain to a soft cotton rag. These stains are available at home improvement stores in a variety of colors.
Rub the stain onto a small area of the cast-stone mantel in a circular motion. Immediately wipe the stain off with a clean rag. Repeat this process to darken the area until you are happy with the color of the mantel.
Continue to rub the stain and wipe it off until the entire mantel has been stained.
Wear rubber gloves when working with phosphoric acid cleaners, as the cleaner can cause skin irritation.
The directions for using phosphoric acid cleaners in this article is a general guide; make sure that you follow the exact directions on the cleaner packaging if they differ from these instructions.