Disclaimer: I don’t claim to be a professional carpenter. I don’t even claim to be an amateur carpenter, because that would mean I might have read a book about carpentry at some point. This narrative is in no way the recommended method of completing this project; I’m just documenting my experience so that others can learn from my mistakes. All the materials here were purchased at my neighborhood Home Improvement Warehouse(s) and tool rental centers, which kept my costs way down.

In a recent copy of This Old House, I found a gatefold article titled “Installing A Mantel”, with diagrams, instructions, and a few prefab examples with links to manufacturers. What amazed me was not the simplistic, breezy instruction list, but the cost of the prefabbed examples-all of them were over $1,000, and none of the featured models matched the simple woodwork in my house.

A year before I found the article, I’d decided to build my own mantel to match the woodwork in our house, a 1925 foursquare. When we bought the house, my wife and I inherited a brick fireplace with a simple slab of oak as a mantel. The brick, from what I can gather, was originally a dark color, and the mortar was set back from the edges by 1/4″, an aesthetic I wouldn’t have appreciated in any decade. To top it off, it had been covered in successive coats of white paint and left to absorb years of cigarette smoke, so that it became a shade of what she dubbed “Phillip Morris White.” The brick hearth was painted black, and a square brass surround was installed (poorly), which kept the heat in the house when the fireplace was not in use.


The first thing I did was to build a simple skeleton around the existing brick, anchoring two support studs into the wall on their sides to reach out past the brickwork. To this framing, I added studs going across the front of the brickwork and down to the hearth, forming feet, and then built out a box for the mantel at the top.

Where it's been

To this skeleton, I stapled some cardboard and whitewashed it as well as possible so that we could get a feel for how large the finished box would be. And there it sat for about eight months, while we worked on the room around it-installing new electric wiring, recessed lighting, and putting in drywall to shore up the old plaster and lathe ceiling, etc.)

When the baseboards were finally ready to go back in permanently, I started to work out how the mantel would look in my head, and how I wanted the diferent elements to look in relation to one another.

Our woodworking is done in a simple style; the doors and windows are framed in 5″ boards with round beveled edges, topped with a 1/2″ beveled cap. Above the cap is another 5″ square-finished board, and on the top edge of this board is a cap molding in a size no longer mass-manufactured. The bottoms are finished off with a beveled “foot” which is a true 1″ thick board, at a height of 4″. (Finding wood to recreate this foot has been lots of fun, but I’ve found that better Lowe’s locations carry 1″ thick pine these days.)

For the face of the mantel, I started by selecting the best sheet of wood I could find in a 4×8′ size, which turned out to be 3/4″ sanded birch plywood. Later, on a return trip to the same store, I found a sheet of 5/8″ MDF for half the cost, hidden around the corner-oh, well. I’ve never worked with MDF before, but I imagine it’s a lot more forgiving than plywood. The moral of the story: Keep your eyes open.

For each of the sidewalls I used poplar, which comes in many of the same sizes as pine, but is usually a better grade and free of knots. It’s a harder wood, which can be more difficult to cut, but the flip side is that it’s usually dry and straight at the store (something the standard-grade pine is usually not.) Wood with knots is harder to smooth and paint, and often sap will drool out of the holes.

I first shimmed out the original frame I’d built to be as square and level as possible. The mantel is actually 3/4″ further from the wall on the left side than the right, so I knew milling the sidewalls was going to be difficult. Once everything was level, I measured off the front of the brickwork (figuring it had been put up level and square, and the house had settled around it) to make sure the front of my mantel wouldn’t stick farther out on one side than the other.

My first step was to cut the sidewalls so that I had square, leveled edges to work from. My original plan was to cut them shaped like an upside-down L so that the leg would form a box for the mantel itself. I measured off the brick once again so that the forward edges were both equally distant from the brick face, and cut two pieces on my table saw down to the right depth. Then I cranked the blade to a 45° angle and cut the bevels on the forward edges. Upstairs, after checking each side for fit, I used a hand planer to shape the backside of the planks to fit the, um, peculiar shape of the wall. After about eight hundred test fits, I got each side to fit the wall correctly and then tacked them into place with some 2″ nails. (Let me just take a moment to preach The Gospel of predrilling any nail holes used to construct anything serious. It’s almost important enough to warrant buying a second drill specifically for predrilling, so that a primary drill can be freed up for other tasks.)

After shimming and fitting the sides so that they were level and equidistant (measure from side to side and then in an X shape from each corner), I moved on to the face of the mantel. First, I set up a straight jig for a circular saw along a short edge of the board and cut down the length with the blade at 45°. Measuring the width of the front face one last time, I set the jig up on the other side and cut it down, making sure I made a straight line with the saw.

Next, measuring the opening, I marked up the back of the plywood for the cutout on the inside. I’ve read in various places about minimum firebox clearances (essentially, keeping anything flammable away from what is called “heat and glow”) and several places mentioned 16″ as a firm number. The This Old House article says “The National Fire Code says that all combustible material must be 1 inch away from the firebox opening for every 1/8 inch it protrudes from the surface, with a minimum 6-inch clearance all around.” I had to contend with the damper handle above the opening, so I used that as my point of reference and measured the sides to fit aesthetically with it. My sidewalls are a little inside 6″, but I found that anything thinner on the sides began to look spindly and weak. (Please don’t rat me out.) The inside walls of the mantel were also going to be beveled so that I could fit it snug to the edge of the brick, but I knew this would get tricky quickly. For the left side of the mantel, the job was easy. I made another jig and ran the saw up to my line.

I clamped a fence for a jigsaw along the top edge, adding 1/2″ to the final measurement so that I’d have some excess on my finished board. Then, I drilled a pilot hole on one side and cut the top edge out. My scrollsaw has a very thin, pliable blade, so it can’t be counted on for a straight 90° cut. I’ll come back to this in a little while.

But here’s where the fun starts. The circular saw will do a 45° angle going one way, but won’t adjust to go the other way, even if the board is flipped on its back. I had to be creative here. Looking through the tools at the store, I found a bit for my router which cut a 45° angle at a depth slightly more than 1/2″, which wasn’t deep enough to go through the entire board.

However, when I thought about it a little while longer, I found a straight bit which cut a square groove at a width of 1/2″, which was exactly what I needed.

What I finally worked out on a scrap plank was this: First, I made a straight 90° cut along the edge so that I could take the entire interior piece out. Then, I flipped the board and routed two parallel grooves along the interior of the cut so that the depth of the remaining board was less than the depth of the 45° router bit. Next, I measured the distance between the edge of the angled router bit and the edge of the router deck, and made a fence for the router to guide it in a straight line. Finally, I cut the edge of the board with the router slowly and carefully, stopping the router about 1/2″ before the 90° angle at the top of the mantel.

Finally, I clamped a fence on the top horizontal cut to clean it up—this is where I used the jigsaw with the flexible blade, remember—and cut as much as I could going one way with the circular saw, then measured, realigned the fence, and cut it to the edge going the other way. Cleaning the edges up with a handsaw, I had both the beveled cuts completed and the face ready to go.

With the mantel and its sidewalls cut, it was time for the first test-fitting. I pulled out the level and tape measure, and tacked the sidewalls into place on the framework. Then, I fitted the mantel face up to the sidewalls and made sure everything aligned and leveled correctly. With some minor trimming to the bottom of the face, the board fit up almost exactly to the sidewalls.

Faceplate installed

Yeah, I know—I’m as surprised as you are. But it actually worked.

Next: Building the box on the top, take one.

Date posted: January 28, 2007 | Filed under house | Comments Off on How To: Fireplace Mantel, Part One.

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