Simple Faux Fireplace Mantle

Lay out an arch across the top edge of the 2x12 header and cut it with a jigsaw. It doesn't have to match a template — a gentle, symmetric curve is the whole goal. Sand the sawn edge until the arc is smooth and even; a wavy jigsaw line reads as sloppy once it's painted a solid color.

The 2x4 inner trim pieces screw to the arched header to frame the opening. This joint doesn't need to be strong — it gets reinforced by the legs and back panel later — so don't overthink it. If you have a pocket-hole jig, use it; otherwise just drive screws at an angle from the 2x4 into the 2x12.

Note that 2x12 stock varies in actual width; measure yours rather than trusting the nominal 11-1/4" and adjust the trim placement to suit.

Set the two 4x4 legs against the sides with their backs flush to the back of the assembly. Counterbore each screw hole first: drill partway through the 4x4 with a bit the size of the screw head, then finish the hole with a bit the size of the shaft. That sinks the head below the surface so it fills and paints invisibly. Fasten the legs to the inner trim with 3" screws.

Screw the 51-1/2" 2x4 top across the tops of the legs with 3" screws. This ties the two legs together and gives the mantel top something to land on. If it looks like a headboard at this stage, that's expected — the frame really is the same idea.

Center the 2x6 mantel top on the top rail with an even overhang front and sides, and screw it down through the 2x4 below. This is the display surface, so keep it flat and its front edge parallel to the wall.

Screw the faux brick paneling onto the front to close off the opening and give the fireplace its face. Keep the fasteners near the edges where trim or the frame will hide them.

Fill every screw hole, sand flush, and prime. Paint the frame the color you want and, if you like the contrast, stain the mantel top instead of painting it.

Before you call it done: drive a screw through the header into a wall stud behind the fireplace. A freestanding surround this tall is top-heavy and will tip forward the first time someone leans on the mantel. This is not optional.