To replace a fireplace hearth, remove the old hearth with a demolition hammer, pour and smooth fresh concrete as a base, and secure the new hearth atop the base. You need a demolition hammer, a chisel bit, concrete mix, thinset mortar and a new hearth.
- Chip away the old hearth
Use cardboard and painter's tape to create a protective cover along the area that surrounds the hearth. Attach the chisel bit to the demolition hammer. Use the hammer to chip away the material of the old hearth gradually. Remove the chipped pieces, and use a broom or shop vacuum to remove debris from the area.
- Create a new base
Cut a notch on both ends of a long, 2-inch by 4-inch board in a way that the board's center fits perfectly within the base, and the notches are able to rest on top of the cardboard outside of the base. Mix the concrete according to the manufacturer's instructions. Wet the bottom of the base, and pour the concrete over the base. Use the notched board to spread the concrete over the base. Use a trowel to smooth the new base. Allow the concrete to dry overnight.
- Install the new hearth
Mix the thinset mortar according to the manufacturer's instructions. Pour the mortar over the base. Use a toothed trowel to create evenly spaced parallel lines along the horizontal surface of the base. Secure suction cup lifters on the top of the new hearth. Place the new hearth on top of the base. If the hearth wobbles, remove and apply more mortar. Apply mortar to the space between the fireplace and the hearth, and smooth to finish.