How to Build a Fireplace Mantel in 5 Steps

Use a measuring tape to take dimensions of your existing firebox or fireplace area. This will help determine the cuts you need to make to your lumber. Sketch a design on paper once you have your measurements and an idea of what you want. Browse fireplace mantel designs online for more inspiration. 

A key consideration is the depth of the mantel shelf. If you’re unsure of how deep to make it, but you plan to place decorative items on it, consider a six-inch deep mantel for ample space.

To ensure your design meets national fire safety codes, you need to leave at least six inches between your mantel and firebox on all sides, plus one inch for every one eighth of an inch your mantel sticks out from the wall. It’s a good idea to create a cardboard template of your design to test how it will fit in your space.

Based on your measurements, use your miter saw to cut the 1-inch by 10-inch pine boards to length for each of the following:

• Mantel shelf: The flat piece rests on top of the mantel and runs its width.

• Mantel face: The front of the mantel parallel with the opening of the fireplace.

• Mantel underside: The opposite side of the shelf.

• Mantel ends: The pieces bookending the mantel.

Use your miter saw to cut edge pieces of lumber for each side. When making the cuts, be sure to cut against the grain of your wood. Sand all of your wood pieces with sandpaper to create a smooth surface that will make painting or staining easier.

Assemble the mantel into a rectangular shelf.  Affix the edge pieces to the mantel face using your wood glue and nail gun. Then, attach the underside piece with the same materials.

Using your stud finder, locate your studs so you know where you can securely attach each end side to the wall. If you’re attaching your mantel to a tile or stone wall, you need to use construction adhesive instead of nails.

Before nailing, place your level atop each end to ensure that they will create a level surface to support the mantel shelf. Run beads of construction glue along the entire length of each edge that makes contact with the wall. Then, use your nail gun to nail your mantel to the wall at an angle.

Finally, attach the mantel shelf to the rest of the mantel by nailing it through the top.

Give your mantel an elegant, finished look by adding decorative molding to each piece. Attach molding by running a bead of wood glue along the mantel's edge. Then secure it in place with your nail gun. You’ll need different molding styles for each part of your mantel, including:

• Crown molding: Top of the breastplate and legs, underneath the mantel shelf

• Baseboard trim: Bottom of each leg

• Astragal molding: Bottom of the breastplate

• Shoe molding: Edges of the mantel shelf

When cutting molding to length with your miter saw, make cuts at a 45-degree angle, so perpendicular accents fit together flush in the corners. Review your saw owner’s manual for specific instructions about the settings required to make an angled cut. You may need to use wood putty to cover visible nail heads and create a smooth finish on all trim pieces.

Once your mantel is assembled and fully sanded, you can apply paint, stain, or another finish to complete the project. Learning how to paint your fireplace is easy if you know where to start. Heat-resistant paint is best to withstand the high temperatures from your fireplace.

Start by lining the area around the mantel with painter’s tape and laying plastic sheets on the floor to avoid getting paint on walls or floors. Apply one or more coats of paint or finish to the mantel according to the instructions on the container, then allow 24 hours for the mantel to dry.