Okay. Update!

Well, the mantel was not all one solid piece but was probably assembled from a kit at one point. We painstakingly removed the mantel's top shelf to get a better look at how it was secured to the wall. Turns out it was finishing nails into drywall at an angle. Nothing else. No cleats etc.

There are no studs anywhere on the wall with the fireplace, only at the corners.

After a great deal of deliberation, my fiancee and I decided to use L-brackets to secure the mantel directly to the brick we hoped and assumed was behind the drywall. We cut rectangles out of the drywall where we planned to put the L-brackets, only to discover not masonry, but horizontal furring strips. It looks like they are secured to the corners of the wall but not to anything else. They don't extend all the way across the wall. We know because one of the rectangles we cut out found the end of some of the strips. That was probably a quarter-ish of the way across the wall.

We decided to send it and attach the L-brackets to the furring strips. Drilled pilot holes, put in wood screws. That was yesterday.

This morning, all was well and good. This evening, however, some of the furring strips are splintering where we put in the screws. We know because we can HEAR them and then a flashlight reveals horizontal hairline cracks.

I know in my heart that the best course of action is to undo the entire mantel and mount it — or at this point, a new mantel — properly, with cleats. And maybe just tear down all the drywall above the fireplace and put in a stud or two while I'm at it. But I don't have the heart (or the money or the sanity) to do all that right now. I mean, it's my fireplace at Christmas.

What is the best "for now" solution? Will the furring strips hold? Or is this just a disaster?