What's the Deal With PVC Trim?
The PVC (polyvinyl chloride) trim we're talking about is also referred to as cellular PVC. It's PVC all the way through. Don't confuse it with high-density rigid polyurethane or PVC-coated products. While they too are highly durable and low maintenance, their installation techniques are different. PVC is a form of plastic that's used in a hundred different ways, including for plumbing pipes.
The trim comes in various thicknesses and widths, but it's most often sold in common sizes similar to other wood trim products. Some companies offer material that has an embossed wood grain side and a smooth side. There are dozens of profiles to choose from: bead board, skirt board, tongue and groove, quarter round, brick molding, coves, crowns, just to name a few. You can even get it in sheets like plywood.
The home center near you might stock only 8-ft. boards in a few of the most popular widths, so you'll likely have to special-order longer lengths and the specialty profiles and moldings. The price is the biggest downside to PVC—it's expensive.
Cement the Joints
One advantage of PVC is that you can “weld” joints to keep them tight and prevent water from penetrating behind the trim. Manufacturers recommend a special type of PVC cement that has a longer “open time” than the type of cement that plumbers use on plastic pipes. You can buy this cement wherever you buy the trim.
You'll have about five minutes of working time to clamp and fasten the joints before the cement sets. Smear a little cement on both surfaces and then clamp or screw the joint together. Wipe off any excess right away with a damp rag. Unlike PVC pipe cement, PVC trim cement is water soluble and won't melt finished surfaces if you remove it immediately.