How to Build a Hearth With Slate

Remove the mantel if it touches the top of the hearth. Insert a pry bar along one side of the mantel where it meet the wall and gently pull it up to detach the nails. Repeat the process on the other side of the mantel and then on the top. Move the mantel out of the way.

Lay cardboard over the floor outside the area where you will install the hearth. If there is an existing hearth, use the perimeter as a guideline. Tape the cardboard down with painter's tape to hold it.

Remove the flooring material inside the areas designated for the hearth. If it is wood, use a pry bar to pull the flooring up. If it is linoleum, cut it out with a sharp utility knife. If it is tile or masonry, don safety glasses and ear plugs and insert a chisel tip into a demolition hammer. Hold the tip at an angle to break up all of the material.

Remove any debris from the hearth area and then vacuum it thoroughly.

Mix a bag of concrete in a bucket outdoors, using the amount of water designated on the bag. Bring the concrete indoors and pour it into the hearth area. The concrete layer should be approximately 1/4 to 1/2 inch below the top of the opening to accommodate the slate. Smooth the top of the concrete out with a trowel and then drag a long wooden board across it.

Wait until the next day and open a tub of premixed thinset mortar. Insert a notched trowel into the tub and scoop up 1 cup of the mixture. Place it in the center of the concrete hearth base and spread it out using the trowel, until it is 1/4 inch thick. Add additional thinset as needed.

Arrange the pieces of slate on top of the thinset as desired. If the slate consists of tiles the same size, insert plastic spacers between them. If the slate is irregularly shaped, arrange them like a puzzle. Tap each slate piece down gently with a rubber mallet to settle it into the thinset.

Open a bottle of grout-release sealer and paint a thin layer on top of each slate piece, using a paintbrush.

Wait until the next day, and open a tub of premixed grout. Scoop out 1 cup of grout using a grout float and smooth it into the gaps between the slate.

Wait until the grout begins to dry, and wipe the surface with a damp sponge to remove the excess grout haze. Reinstall the mantel.