How to Build an Easy DIY Fireplace Mantel From Scratch in Just 5 Steps

Measure and Create a DIY Fireplace Mantel Plan

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 how deep to make it, but you plan to place decorative items on top, consider a six-inch mantel to allow ample space.

To ensure your design meets national fire codes, you’ll need to leave at least 6 inches of space between your mantel and the firebox on all sides, plus 1 inch for every eighth inch your mantel sticks out from the wall. Try creating a cardboard template of your design to test how it fits your space.

Cut Your Lumber

Based on your measurements, use your miter saw to cut one-by-ten 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 legs: Columns on either side that extend from the floor to support the shelf

• Breastplate: The middle piece above the firebox, below the shelf, and between the legs. You may choose to use more than one board or to create a decorative arch over your firebox. Otherwise, you can leave it simple and straight.

Use your miter saw to cut edge pieces of lumber for each leg. You’ll need four identical edges between 1 and 1 1/2inches wide and the length of each leg. These smaller pieces will fit on either side of the leg columns against the wall, giving the legs a three-dimensional look that pops out, so they're not laying flat against the wall.

When making cuts, be sure to cut against the grain of your wood. Sand all your wood pieces with sandpaper to create a smooth surface that will make painting or staining easier.

Assemble the Mantel

Photo: LOOK Photography / UpperCut Images / Getty Images Plus / Getty Images

Use your edge pieces to create a three-sided box for each leg. Affix the edge pieces to the main leg pieces using your wood glue and nail gun. Using your stud finder, locate your studs so you know where you can securely attach each completed leg column to the wall. If you’re attaching your mantel to a tile or stone wall, you’ll need to use construction adhesive instead of nails.

Before nailing, place your level atop each leg 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 legs to the wall at an angle. Repeat this process for the breastplate, which you’ll position between the legs.

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

Add Trim and Molding

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.

Finish Your Mantel

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.