So bear with me, this is the first instructable I've created, but I wanted to share my experience finishing and installing a large beam mantel on an existing stone fireplace. My challenges were how to ensure a solid and secure attachment to the fireplace itself and have the beam look like it had always been there vs. just thrown up on the wall. My other challenge was creating corbels (brackets) to be installed under the mantel that were created out of the same material as the beam. I documented the whole process for myself along with others who might have similar task. Enjoy!
Step 1: Picking Your Wood
Repurposed wood comes in all shapes and sizes. In the case of my mantel we used an 8 x 8 white oak beam. I was lucky to find a beam that was used in a timber framed house. It had the original mortise and tenon slots and even the remains of the pegs used to connect the posts. You'll see in my photos I incorporated those in the design. A couple things to look out for when picking your beam. Look them over carefully for rot and insect damage. Even if the place you buy it from stores their lumber in a controlled in environment, there is a history to all wood that you would rather uncover before you fork out the cash! In my case, my beam had a substantial amount of insect damage that I missed when I purchased it. Luckily, and you can factor this variable in if needed, I wanted to plane down the surfaces of each side of the beam anyways. I was able to eliminate the really bad wood damage, but had to plane down the face of the beam almost 3/4"! I would also factor at least three feet more beam than you need. You will want room to pick an ideal place to cut the beam to size, but you will also need the extra waste to create the corbels. Sorry, I don't have a picture of the original beam before I modified it, but here it is after I milled it the sizes I was looking for.
Step 2: Hollowing Out the Back of the Beam
After getting the beam to the correct size (note: I have not sanded to finish), I then started prepping the mantel for it's future install. After doing my research, I found that hollowing out the back of my beam to later be slid onto a cleat secured to the stone was the best option for me. In order to take a decent chunk out of the back of this beam I used a circular saw and kerfed the beam. I would then chisel out the remaining debris in the hole. I screwed a board on each end to provide a stop for my saw. This kept me from having to think when to stop, and it also prevented me from twisting my saw. Twisting the blade in this application could definitely cause kick back from the saw. I then took a sonicrafter (oscillating tool) to clean up the ends. It took a bit of time, but a flat bar was enough to break away some of the kerfed material and then I used a chisel to clean up the hole. In this case, the hollowed space was 2 1/4" deep. I left 2" of material at the top beam to make sure I had enough meat to screw the mantel onto the cleat once installed. I then fitted a cleat in the space to make sure it sat evenly and went in with out fighting it. Another plus side to this method was that it reduced the weight of the mantel itself. I had thought about taking a large spade to drill out more wood to lighten it further, but with my beam only being 6' long it was light enough.
Step 3: Filling in the Holes
In my case, I had two holes from the where the beam was mortised that I had to fill in. I also had to fill in the peg holes on the face of my mantel. I just cut two blocks with a slight bevel to pound snuggly into the two large holes. I fit the blocks until I could get them about a 1/2" from their final resting place and then removed them to be glued up and hammered in. You definitely don't want them to be forced too tightly or you risk cracking the mantel. As long as they are snug the glue will do the rest. As for the pegs, I lucked out and there were enough good pieces left to salvage. I cut all the pegs so that all the rotted wood was gone and then rearranged them so that they went into the hole that would fit tight. Again, glue will do the rest! I definitely recommend getting ALL your planing of the surfaces done before doing this step. Running a planer over the grain of these pegs and filler blocks could damage them.
Step 4: Creating the Corbels
The corbels were created from the scrap pieces cut from the mantel itself. First, decide the depth and height of your corbels and cut a chunk out of the beam material this size. As for the length, I made mine long enough to do all my shaping first, and then cut my corbels out of that length (see pics). Once I had my chunk of wood, I shaped the corbels using my miter saw. I set and locked the depth my saw would cut and then kerfed all the way along the face of the wood. Once I had my kerfs done I busted away all the extra debris and then set my saw slightly deeper than it originally was set. I then slid the chunk of wood to pass by the saw blade cleaning up all the kerf marks. Two things to note in this step. Take care in your process, because you are working close to your valuable appendages! Secondly, it's hard to guess what the wood looks like inside of the piece you are making the corbels from. My first corbel, once I cut all the kerfs away, had one of the original cracks running all the way through it. It ultimately fell apart and I had to create a new one. These cracks were well worth the effort though. The corbels match the beam perfectly!
Step 5: Finish the Beam
What I thought would be the easiest step, was definitely the most time consuming. After planing down the sides of the beam, it then needed to be sanded smooth. I used a belt sander and orbit sander for this process. I started with 60 grit paper and worked my way up to 120 at the end. While sanding I purposely allowed the sanders to run a bit wild to keep a more natural surface. I also sanded the edge of the beam allowing it to have a wavy, more natural edge when finished. Although there is a lot of freedom for keeping "character" in the wood, the last thing I wanted was to see my planer marks in the finished beam. Lighting is important in this step to be able see discrepancies in the raking light. I'm a bit picky though. We then finished the beam with a stain and poly. This wood looks great natural too! A simple poly will bring out the depths of color and grain in the original wood. This project just called for a darker finish.
Step 6: Installing the Beam
To install this beam we first had to determine the height to place our cleat. I apologize, I did not have pictures of this process. You definitely want to check codes for space required between the fireplace opening and combustible materials. Once you have your desired location trace the outside perimeter of your cleat onto the stone. I also shaded the high rocks with a pencil to come back with a grinder to flatten the surface of the rocks and give the cleat more surface to attach to. I recommend having an extra hand available to hold a vacuum up to the blade while grinding. Dust will be everywhere otherwise! We then located our studs and drilled through the rock using a hammer drill. We installed our cleat using 1/2" lags 12" in length. Every situation is different, but ultimately we wanted our lags at least 2" to 3" into the studs. Once we began installing the lags we shimmed any big gaps between the stone and the cleat to keep our cleat from tipping or twisting. Once the cleat is secure a dry fit of the mantel will give you an idea if any other spots in the stone need to be cut away. What I didn't want it was the beam to look unnatural so we refrained from trying to get it super tight to the stone. Instead we allowed a 1/2" or so of gap where needed and focused on keeping the mantel level and looking straight. Once it was positioned appropriately we glued up the cleat with construction adhesive and then used 3" deck screws (predrilled) every 12" across the top of the mantel. Check it one more time for level and then also secure the bottom with two screws, to be covered up by the corbels when installed. The corbels were installed using liquid nails and a couple trim screws angled into the bottom of the mantel to hold them in place until dry. Predrilling these is also important to prevent ruining the integrity of the corbels. And there you have it!