Manufacturers have used polyvinyl chloride as a material for water pipes since the mid 1900s, More recently, PVC is being fashioned into synthetic lumber for decks and other homebuilding projects. PVC lumber is a premium material -- more expensive than composite lumber materials; it is impermeable to moisture and won't swell or develop mold problems. You can cut PVC lumber with conventional wood saws, but you glue boards together in the same way you glue PVC pipes: by using solvent-weld cement. The cement softens the plastic and actually fuses the boards you are joining into a single piece.
Dry-fit the boards you are joining carefully before you apply any glue. Mark the exact positions you need to place them, using a pencil. The glue has a very short open time -- less than a minute -- and you have to work quickly once you apply it.
Separate the boards and spread solvent-weld glue liberally on both surfaces using the applicator that comes in the container.
Press the boards together immediately after spreading the glue, and clamp them together with C-clamps or bar clamps. Tighten the clamps enough to close the joint. Avoid excessive pressure, or the glue may soften too much plastic and the boards may deform.
Leave the boards clamped until the glue dries, which takes two to three hours. Chip away any dried glue that squeezed out of the joint with a chisel after you remove the clamps.