How do I Build a Fireplace Arched Mantle?

Draw a sketch of the arched mantelpiece you want to build. Use this sketch as reference for the necessary measurements of the various pieces of lumber needed to build each part of the mantelpiece.

Measure and mark the locations needed for the cleat supports or backing supports for the various molding levels on the mantelpiece. These measurements will be determined by the locations and heights drawn in your sketch for each layer of molding. Use your level to draw horizontal lines to make sure the cleats will be installed correctly. Attach the cleats to the wall above the fireplace using the nail gun or masonry screws if the wall is stone or brick.

Cut the lumber for the legs of the mantelpiece to the sizes specified on the sketch using the chop saw. The lumber may need to be ripped to size on the table saw if it is too wide. Glue the sides of the legs to the face of the legs then nail them together. Position the legs on either side of the fireplace and nail them into the cleats to secure them to the wall.

Measure and cut the front of the mantelpiece or the frieze board to size. Locate and mark the center of the frieze board. Draw a very light pencil line up the center. Measure from the bottom of the board up the line the desired distance you want at the peak of the arch. Scribe an arch from the lower corners of the frieze board to this point marked in the center. Cut out the arch with a jigsaw.

Fur out from the cleats by nailing pieces of lumber to the cleats to create the desired depth between the frieze board and the wall. Nail the frieze board to the added lumber. Mark on the frieze board the locations of the molding pieces.

Attach pieces of lumber to the frieze board that will be nailing supports for the various layers of molding. Working from the bottom up, attach the first piece of molding to the frieze board by carefully nailing it to the frieze board and to the support pieces. Add in more support pieces as needed for the next layer of molding. Overlap the next layer of molding over the bottom layer of molding and attach in the same fashion as the first. Continue to overlap and attach the desired amount of molding designed in your sketch.

Measure, cut and nail in the final supports at the top layer of molding. These will also function as supports for the mantel shelf. Measure the entire width and depth of the mantelpiece prior to adding the shelf. Decide how much overhang you want the mantel shelf to have and add that onto the previous measurement. Cut the mantel shelf to size. Lay the mantel shelf on top of the mantel, line it up accordingly, and nail it in place.

Measure and cut a thin piece of lumber that can bend around the inside of the arch to hide any openings or gaps. Nail it in place. Add any desired trim or decoration to the mantelpiece.