When last we left the fireplace mantel, I’d finished adding wings to the sides of the box on top to make the structure look proportionally correct. The next step was to find molding of some kind that would fit the top of the box, mimic the molding in the rest of the house, and have it be approximately the right size.
This is the basic crown molding sold at Lowe’s and Home Depot, clamped into place for test-fitting and basic aesthetic testing. At first I had it lined up with the top of the box, so it began about 4″ down the box and (to my mind) was squishing the top box too much proportionally. My initial plan was to tack it into place here, then see if I could have a 3/4″ plank planed down to 1/2″ at a lumberyard somewhere and basically just tack it on top of the molding. This would have left me with a thick lip at the top of the mantle though—the squared top of the molding is about 1/4″, plus a 1/2″ board == eccch.
My second thought was to mill the sides of a plank down to fit the bevel of the molding (tip: all crown molding is essentially a thin board turned on its side so that it doesn’t create a 45° wedge at the back, which makes it undesirable for finishing the top of, say, a mantle) and fit it to the mantle, then tack the molding onto it and into the side of the box. This would be considerably more difficult but the end product would be much more pleasing.
Another thing to note is that with this particular crown molding, the angle at the back is not a perfect 45°; it’s somewhere around 32°, which makes fitting the bevel that much trickier. I cut the molding according to the measurements and test-fit it, then measured both the box and the outline of the molding to find the final edge size. (Sure, your fancy “New math” might have helped here, but remember, this house is out of square in five dimensions.)
Cutting the long edge of the plank was easy on the table saw, but cutting the short edges was tricky because my compound miter saw only has a reach of about 7″, and this board is 8 1/4″ wide. So I had to revert to the circular saw, adjusting the blade by guesswork and praying for good results.
And luckily, it seemed to work. I got true 32° cuts from the circular saw in a straight line, and fit the plank into place. Next, I had to jigsaw out the odd scalloped shape of the bumpout above the fireplace into the back of the plank—both edges come out about 1/8″ further than the center— and plane out any inconsistency left so that it fit as flush as possible.
The end result has a few very minor hiccups here and there, but overall looks very good, and turned out better than I’d dreamed it might. I have to cut and fit shims on the top to support the plank, and then the whole thing gets permanently fastened to the frame.
The next step is to cut down those small planks on the right side and fit them around the sides so that they meet the kickplates on the wall, covering up the lousy edging job the floor guy did around the fireplace and the lousy brickwork we inherited. Then, putty and caulk go in to fill any rough edges, a final sanding, and finish paint goes on.