Wood has long been a popular material for exterior trim. Wood trim is available in either solid boards or finger-jointed pieces. Solid wood trim made from heartwood of western red cedar or redwood is easy to work with and resists rot and warping. Southern yellow pine and Douglas and Hem fir are also popular wood trim choices, since they cost much less that the cedar. Solid wood trim is easy to install and takes paint well, if the wood is vertical grain heartwood.. Finger-jointed wood trim is simply shorter wood pieces that will lock together. Finger-jointed wood is often glued together at the mill to create pieces as wide as 10 to 12 inches. If the finger-jointed wood trim is not protected well, the joints will show through the paint after time.
There are two main types of plastic trim, polyurethane and polyvinal chloride (PVC). Polyurethane is slightly more expensive, but is slightly denser and comes ready to paint, whereas PVC needs to be sanded before paint is added. High-density plastic trim is more durable than wood and is easier to install. All plastic trim can be molded into intricate designs that can resemble expensive hand-carved wood. Plastic will not rot and will not shrink or swell like other trim choices.
Fiber-cement trim is a combination of Portland cement, sand and wood-fiber reinforcement. It is durable, fire resistant and immune to water and insects. Most fiber-cement trim is a little difficult to work with, it has to be cut with a carbide-tip blade on a circular saw and the blade will normally have to be thrown away after the job. Some fiber-cement trim manufacturers claim that their fiber-cement can be worked with using the same tools that are used on wood. Fiber-cement is moisture resistant so paint will last a very long time, since stress will not build up under the coating.
Laminated Veneer Lumber
Layers of wood veneer in a parallel grain and two veneer cross band are covered by a medium density overlay to create laminated veneer lumber (LVL). LVL is easy to cut, nail and install. LVL trim is stable, so it won’t warp or bend like wood. LVL trim will take paint well and is available is a number of different widths.
Hardboard trim is made from hardwood chips that are heated with steam and water and then pressed into board stock. During the pressing, lignin that is normally found in wood cells begins to flow again and works as an adhesive to hold the board together. This lignin also helps make the hardboard a little more resistant to decay than wood. Hardboard is a little difficult to install, since installers have to be careful not to leave any openings, like in nail holes, where water can get in and destroy the hardboard. Hardboard is also susceptible to swelling as the compressed wood fibers expand over time.