Craftsman Mantle

This simple looking mantle is deceptive in appearance. In fact, the brick fire place surround is 13 feet wide. The finished mantle is 12' long, 15" deep and 6" thick. The span between the brick corbels is almost 9 feet. All this created some interesting engineering and material problems.

The design seems simple enough, but the scale creates some issues. This mantle is made of white oak to match cabinets elsewhere in this room. In order to maintain the clean, craftsman style of the room and cabinets, the mantle needed to be simple and unadorned. The real problems was that white oak in only readily available in boards up to 8' long. So I spent over a week tracking down a supplier with long enough boards for me to make the mantle without unsightly joints in the middle of it (which was the number one design priority of the homeowner).

The next big issue is weight and rigidity. Because of the wide span and narrow profile, the mantle needed to be absolutely rigid, yet light enough to be supported by anchors in the brick, and strong enough to carry the extra weight of whatever the homeowner might want to display on it (probably that TV which is 150 pounds!)

The solutions was to build a torsion box. The problem is that a t-box requires continuous skins across the top and bottom, but plywood (the material of choice) also isn't readily available in sheets longer than 8'. So once again there was a problem.

With all these problem, it's no wonder 4 other contractors had told the homeowner it couldn't be done the way she wanted it. But obviously it could, it just took some creativity and planning.

After locating the 13' white oak boards, I spent the better part of a day resawing them (with the help of a friend) into 1/8" thick veneers, and making two pieces of custom cove molding on the table saw. (next time I'll pay the $500 to have the 17' of molding made! what a nightmare!) When the day was done, I had 17' feet of very rough cove molding and six 13' long veneers.

Because this project is so long and involved veneers and a torsion box, I needed a custom, completely flat work surface. I set up 4 saw horses, topped with 2x4's. On top of the 2x's I placed 3/4" MDF sheets. Then I used a 78" level and shims to remove any dips and waves in the deck. Finally I screwed through the MDF into the 2x's to make sure nothing moved. I didn't allow the table to be moved for the remained of the project since doing so might through it off and effect the entire project.

The next step was making the 1/2" plywood I needed. By laminating layers of 1/4" plywood together with overlapping seams, I was able to create continuous sheets 12' long. The key to doing was the vacuum press, which creates even pressure across the entire surface. The end product was 3 long, very flat pieces of 1/2" plywood for my torsion box. As you can see, 12' is the very limit of what fits in my largest vacuum bag!

Next I veneered two of the plywood pieces with the white oak, again using the vacuum press. Normally it's important to apply veneers to both sides of a substrate to prevent curling. But since the unveneered sides would be glued to the t-box grid, curl was not going to be an issue.

After coming out of the bag, all three plywood sheets were stacked with stickers to allow even air circulation and allowed to dry completely over night.

Then I assembled the Torsion box, with the unveneered 12' plywood to form my long front and back sides, and pieces of normal 1/2" plywood for the rest. I used the vacuum bag again to glue the previously veneered bottom on. The vacuum bag's even pressure eliminated the need to dozens of clamps and cauls. And because I took the time to make a flat table earlier, I was assured a flat torsion box. (Even with only the bottom skin, the box supported itself without bowing when balanced on my table saw!) Then I use the press again glue the two pieces of 1/4" ply (seamed over a rib) to the top of the t-box. (this is only part of the final top, it's seam would be reinforced later).

Now I applied the cove and a 1/4" bead at the bottom. I reinforced behind the cove with wedges of plywood glued in place. Then glued the top skin to the t-box and cove. By now the mantle was too big to fit in my vacuum bag, so I clamped it upside down to my table with cauls to ensure even pressure and a good bond.

After the top was glued on, I applied a 3/4" x 1" edge to the face and sides to cover the exposed layers of plywood and create a lip over the cove molding. I profiled this lip with a 1/4" round over top and bottom.

What followed was more sanding than I want to think about. The hand sawn veneers and table-saw-made cove were extremely rough and required hours of sanding. Because white oak is so hard, this was tedious work. In the future I will buy a wide drum sander and molding machine or pay to have these things sanded by an outside source. It just is not economical to do this by hand.

Finally it was time for the finish. To enhance the grain, improve the smoothness of the final finish and replicate the oak cabinetry in the room, I used a tinted grain filler. This photo shows the unfilled oak (bottom right), the filler after application (bottom left) and the final result after removing the excess filler and lightly sanding (top). The enhanced grain is much more visible to the eye and smoother to the touch.After filling the grain, the whole thing was stained, sealed, toned, and top coated.

Installation, with the help of a friend, took a few hours, mainly due to drilling into old, hard brick for the mounting anchors. Before delivery I weighed the mantle, 90 pounds (using solid oak it would have weighed 350 pounds). I used 10 anchors so each carries less than 9 pounds, plus when you consider much of the load is carried by the brick corbels, there's no fear of the mantle falling off the wall.

In my shop I had a lot of anxiety about the mantle due to it's size. It is almost twice as deep as most mantles and monsteriously long. In my shop it looked awkward and disproportionate. But I had done scale drawings and had to trust it would all work out. And it did. Installed it looks at home on that huge brick fire place and it's size is proportional to everything else.