How To Splice Lumber
by Damien Andrews
Today, there are so many options available for splicing together pieces of lumber that no single article could even begin to touch on them all. So let's narrow the scope of this treatise to: a) splicing dimensional lumber (sometimes referred to as stick lumber) and b) using what most do-it-yourselfers would have lying around the shop. If your project(s) call for the frequent splicing of dimensional lumber, you would do well to look into some of the various metal wood joiners. Metal wood joiners come in all sorts of shapes and sizes, and make quick work of splicing dimensional lumber for virtually any application.
For purposes of simplicity in this article, we'll be working with the most popular dimensional lumber size: the 2" x 4". In the following artwork, A, B and C all represent 2" x 4"s of unspecified lengths. Now, let's start splicing.
First, make sure that the two butt ends of A and B that you'll be joining are perfectly square. A miter saw makes quick work of that task. When that's done, lay the two pieces of wood out, squared butt end to squared butt end, for splicing.
Second, cut C to the appropriate length. The length of C will depend on the lengths of the two 2" x 4"s you intend to splice, and their intended purpose. A longer splicing piece will be stronger, and allow more space for securing it to A and B. Bear in mind the use of the spliced lumber when deciding what length to cut C. For example, if you are splicing the sole plate on a wall you're framing, then the longest C could be is 14", otherwise it will interfere with the spacing of your 16" O.C. studs. Once you've cut C to the appropriate length, mark the center of the long axis – as shown in the diagram.
You're now ready to splice the lumber. All you need are some 8d nails (2½" long) or some 9d nails (2¾" long). Put A and B on a flat surface with one edge placed against something perfectly straight, such as a wall. You can also use a straight piece of lumber, or the factory edge of a sheet of plywood. This ensures that the final spliced piece will be perfectly straight. Press the squared butt ends of A and B tightly together and then place C on top of them, with the center line directly above where A meets B (as shown in the diagram). Now, nail C to A and B as illustrated in the diagram. Voila – you're done. This is a very strong and effective splice, but let's look at ways to make it even stronger – for those applications that require it.
After you parts are cut and ready to assemble, put some wood glue on the meeting butt ends of A and B. After pushing them together, put some wood glue on the bottom of C and then nail as mentioned above. This will require drying time, but will be very strong. PRO TIP: most people put newspaper under glued joints to stop the excess glue from dripping onto the floor. If you use plastic, such as a cutup trash bag, the glue will not adhere to it, nor will the plastic stick to the wood. This eliminates the need for sanding the glued newspaper off the finished splice.
Using screws instead of nails will require pre-drilling, but will make the joint stronger and also help ensure that the lumber does not shift during the impact of nailing. 2¾" screws are ideal for this. #6 wood screws will work great, use #8 wood screws for additional strength.
Using a plywood gusset (or two) will dramatically increase the strength of the splice. Gussets are not always practical as they make the edges of the spliced lumber unusable in many instances, such as when you intend to install sheathing or wallboard. In the diagram, the gusset is not cut to match the profile of the splice, but it could be if that was called for. Attach the gusset(s) with nails or screws – glue is optional.