How to Fix a Crack in a Stone Mantel

Identify the stone used for the mantel, which is commonly a material know as “cast stone.” This is a type of concrete mix manufactured to simulate natural stone, and it was used extensively when mantelpieces were fashionable in older homes. The basic ingredients of cast stone include water, sand and coarse aggregate such as gravel and cement, and it may have a variety of finishes such as sand-impregnated paint.

Observe whether the crack is located over a joint. Joints in older, cast stone installations may be thin, while cracks are common on exposed sections of stone such as a balustrade or “coping,” which is the sloped top of a section of stone. A crack over a cast stone joint is more difficult to excavate and can result in a separation of the joint, which will require major repair or replacement.

Use a hand-held grinder or a hand chisel to remove the section of stone surrounding the crack, to a depth of approximately 2 inches. This will enable you to “patch” the crack, which should provide enough protection to last a few years. If the crack is much deeper than 2 inches, you may not be able to fix it and might have to replace the mantel instead.

Mix small, test quantities of mortar, and add paint in a color resembling the stone. Allow the test lots to dry, and determine which matches the original stone closely. Alternatively, use uncolored mortar mix to fill the crack using a trowel, and paint the entire mantel with paint in a color of your choice.

Combine your paint with coarse sand aggregate to give the finished mantel a fresh, stone look. The amount of aggregate used depends on how rough you would like it to look, with a larger quantity resulting in a more rustic finish. Add small quantities of aggregate to the paint and test it each time until you have the texture you want.