Wide panels are made by gluing two or more boards together. The boards need to be straight and their edges must be perpendicular to their face.
The key to making large panels is preparing the edges of the boards to be joined. If you have access to a table saw and a jointer, you can rip the boards and then use the jointer to smooth the edges. You can also acquire a planer blade for your table saw that, when set up properly, will cut the edges so smooth that they can be glued up straight from the saw. Planes and routers can also be used for straightening and smoothing the edges.
The boards should be arranged so that their color and grain match well enough that, when glued, the boards look like one piece of wood. You should also try to arrange them so that the end grain patterns alternate. (See Illus. GP-1) You should make the panel an inch or two longer and wider than its finished size to allow for final trimming and sizing.
The boards need to be properly dried. Some woodworkers even go so far as to store their kiln dried lumber, for a couple of weeks, in an environment that has the same temperature and relative humidity that the finished project will be used in.
Although using dowels or biscuits to reinforce the joints is not mandatory, it does strengthen the joint and aids in alignment during the gluing process. Another method is to use a router, fitted with a WOODCRAFT Adjustable Thickness Finger Joint Bit to cut a "finger joint" along the edge of the board. This finger joint adds more surface area to the joint, allowing more contact area. It is a good idea to dry fit the boards together before gluing them. It will help you identify any edges that are not straight and smooth.
There are several types of glue that will hold panels together, but generally yellow glue is the best. Titebond II works well and can be used for outside furniture. The ultimate glue for external use is polyurethane glue such as Titebond Polyurethane.
Be sure to use only enough glue to cover both sides of the mating pieces. Excessive glue can prevent the boards from making solid contact with each other. When you clamp the boards together, using pipe or bar clamps, glue squeezing out of the joint is a good thing. It shows that the joint has enough glue and is thoroughly covered. This excess glue must be completely removed from the wood. Most woodworkers wait until the glue begins to set up or gel and then scrape it off with a putty knife or chisel.
Make sure that you do not over-clamp the panel. If you apply too much pressure, the clamps may bow and leave you with a cup shaped panel. It is a good idea to place the clamps on alternate sides of the board. Alternating the clamps helps to eliminate cupping the panel because the clamps pull against each other.
To determine how long to leave the boards clamped, follow the instructions on your glue container.