I get asked - a LOT - how I join pieces of wood together at structural joints when building furniture. Most people, outside the woodworking/furniture-building world, assume it's some combination of screws, nails, dowel rods, etc. Those people are usually surprised when I tell them that I typically use glued mortise and tenon joints, as have craftsmen for literally thousands of years, and no mechanical fasteners of any kind.
There are an almost infinite number of ways to join pieces of wood together, but the mortise and tenon joint has to be one of, if not the most common type of joint in well-made furniture. So, what does a mortise and tenon joint consist of? Well, a mortise and a tenon. :)
The mortise, which for my money is the more crucial of the two components, is shown in the above picture on the righthand side. It's the hole, or slot, that the tenon fits into. I should mention that the joint being shown in these pictures is not a true mortise and tenon joint but more of a hybrid open mortise bridle-joint (but for all intents and purposes, it's a mortise and tenon joint). That said, most builders prefer to cut the mortise first, as it's easier to shave material off the tenons until a proper fit in the mortise is achieved than it is to cut the mortise exactly right to fit a tenon.
There are a variety of ways to cut mortises, and I prefer to use my router with a spiral bit. I avoid using a jig if I can help it, as jig construction sometimes takes more time than cutting the actual mortises does. I set up the router table, get the fence where I need it, and start blowing through material. I don't worry too much about the bottom (or top) end of the mortise cuts, as I fine-tune those with a chisel. The router cuts circular holes and tenons are usually cut with square corners, and everybody knows you can't put a square peg in a round hole. Hence the chisel work, to square up the mortise bottoms (and/or tops).
With the mortises cut, the tenons, shown in the above picture on the left, can be cut to fit the mortises. In general, it's a good idea to cut the tenons so that there's a hefty amount of material remaining, with just enough shoulder around the tenon to provide a clean edge and structural integrity during clamping. I normally cut tenons on my table saw with a dado blade, and I typically try to cut the tenons as long as I can but it's all relative to the size of the lumber in the joints and the type of project I'm building. Likewise, I think most people - myself included - don't aim for perfection with the first series of cuts. It's easy to continuously remove material, but if too much material is cut off...it's time to start over. The idea is to cut the tenon so that it fits fairly snugly in the mortise, but not so snug that you need to beat it into place. Patience goes a long way in cutting tenons.
At the end of the day, the tenon serves two purposes: 1, to provide strength so that the load carried by the rails of a piece is transferred to the posts (AKA, provide a joint so that the rail can be supported by the post), and 2, to provide as much surface area as possible to which glue can be applied. With the mortises and tenons cut, glue can be applied to all surfaces and the joint can be clamped.
Once the glue dries, it's stronger than the wood it's holding together and, if done correctly, the joint should last for a really, really, really, really long time, and definitely longer than any kind of mechanical fasteners.
We've been busy the past couple weeks taking care of a number of projects for the owners of a new yoga studio, Namaste, and Sol, an organic sunless tan and spa studio in downtown Kirkwood, MO. One of those projects was a custom tile countertop for Sol's reception area.
Because the countertop is cantilevered on both sides and will probably be leaned on and bumped into from time to time, it needed to be built rock solid. To accomplish this, we glued and screwed 3/4" plywood to the existing metal framing, laminated a 1/2" sheet of plywood to that, and then screwed and thinset a sheet of 1/4" HardiBacker to that.
With a solid, 1.5" thick tile-ready surface constructed, we then installed the mosaic field tile and hefty bullnose border. Cutting the miters for the corner bullnose tile took some ingenuity and creative tile saw usage, but as always, we pulled it off.
Because the border tile was thicker than the field tile - and the clients wanted everything flush - we had to build up the thinset under the field tile, which always creates a challenge with mosaic tile installations as the thinset sometimes has a way of squeezing between the mosaic tiles and creating a giant mess. However, in these situations one must pick and choose their battles, and we chose to deal with the excess thinset later on, once all the tiles were installed and the thinset had set up for a while.
Once the thinset was cleaned up, which took some time given all the nooks and crannies in the field tile, we applied a simple white, non-sanded grout to complete the project and give the clients a simple, clean countertop that should be relatively indestructible.
Today I got to meet and talk rehabbing with a couple guys who have a real big vision, and tour a couple of their properties...a pre-bid meeting of sorts. The smaller of the two houses, located in the Dutchtown South Neighborhood, is one of the oldest houses in the area and rumored to be almost 150 years old. The larger property, originally a two-family, will be converted to a single-family residence and is located in the Forest Park Southeast Neighborhood, home of The Grove. The owners are looking for subcontractors and possibly, on the larger project, a general contractor. I would really, REALLY, like to be that general contractor, and hopefully we'll get that opportunity.