My house was built in the 70s, and the fireplace room looks like it! While the brick wall and concrete mantle have proven to be solid for holding just about anything, it isn't the most attractive or contemporary design.
To give our fireplace a more contemporary feel, I bought a pile of discount boards (2x4s, and 2x6s) from a local wood seller and started taking measurement to retrofit a wooden mantle over the existing (and quite solid) concrete mantle.
This is how I did it!
1. Lots of wood. Preferably 2x4s, 2x6s, and/or 2x8s. The wider the planks, the quicker the building of the top goes
2. Lots of construction screws
3. Concrete screws (or drywall screws, if your back wall isn't brick)
4. Wood glue
5. Two-inch shelving brackets
6. Linseed oil (or whatever finish you prefer)
7. Poxy (for the finishing touch)
1. Electric drill
2. Impact drill (especially for those concrete screws)
3. Sand paper (preferably an orbital or belt sander... makes things way easier)
4. Miter saw
5. Measuring tape (this is crucial!)
6. Non-marring hammer (the orange ones)
Optional 7. Hammer drill (which isn't necessary, but definitely helpful for putting holes in brick and mortar)
Step 1: Old Adages Die Hard
The old adage, "measure twice, cut once" is so painfully obvious yet vital to a build like this. I had to go back to the local wood shop a couple times because I mis-measured wood on the initial cuts.
Since I was building a wooden mantle to place on top of the old mantle as one piece, I needed to make sure I had clearance on both the inside edges (next to the brick) as well as the inner side of the outer boards (to essentially, wrap the former mantle).
I wanted to keep any attaching mechanisms hidden, so I also kept the inside measurements a little tight. This way, the mantle structure really squeezed onto the former structure, providing a solid surface before the final attachment.
Using a standard miter saw and some metal shelving brackets, I measured the wood to size.
Step 2: The Start of Assembly
Once all of the cuts were made, I started the loose assembly with the brackets. The brackets are decent for keeping things in place, but they can't sustain much weight, so everything was reinforced later.
Step 3: Completed Assembly
Once the brackets were in place, I added a bit of wood glue on the inside seam of each board, just to keep things tight.
After attaching all of the top boards to the original 3-piece framing, I added 2x4s to the underside to add a little more beef to the piece and for extra support. Again, this piece was placed over an existing concrete mantle, so as long as the boards stayed together and were even, the structure was sound.
I wanted to keep a raw wood feel with this mantle, so I didn't do any sanding until the entire assembly was finished.
Step 4: Final Touches
After a light sanding, I placed the new mantle over the concrete monstrosity. With some light tapping from a non-marring hammer (one of the orange ones that feels like it has sand in the head), I squeezed the wooded structure into place. Once secure and level, I attached a couple more brackets to the underside of the mantle and concrete screws to attach the structure to the brick.
A little linseed oil and a couple coatings of satin clear poxy and I now have a brand new mantle!