How to Use Synthetic Trim

Many of us who work on our homes consider wood the material of choice for moldings. Yet more and more space on home-center and lumberyard shelves is devoted to synthetic trim. Although the techniques for installing these PVC and urethane products are the same as for working with wood, synthetics differ in everything from design details to paint requirements to what you can do or make with them.

The Benefits of Flexibility
Synthetics are famous for flexibility, a feature that pays off when you’re dealing with uneven drywall, plasterboard or plaster surfaces. Because the molding is flexible, it can conform to crests and troughs along a ceiling or wall much better than wood moldings (photo, below), and as a result, the caulk joints are smaller, giving a more polished look to the trim. (Note: Some undulations are too severe and should be evened out with joint compound before you install molding. In old houses, we like to pull a string along the ceiling in a few places to see how uneven it really is.)

We often custom-make our wainscoting top caps using 1x and a router, and we like using PVC in old houses where the drywall or plaster undulates. The PVC follows those imperfections and closes up gaps that would otherwise require a lot of caulk.

In addition, you can use PVC 1x as a template for laying out round or elliptical shapes instead of doing calculations. And the material bends uniformly around objects such as a radiused Roman bath step, an arched fence detail or a curved garden bed.

Other advantages
One common trick with wood trim is to layer a piece of base molding under the crown at the wall or ceiling to give it more dimension. This approach looks great, but installing extra layers takes more time and makes the project more complicated. Synthetic molding offers the built-up look with no extra layers because the entire profile is a single piece (photo, below).

For a “built-up” look, it’s hard to beat synthetic molding’s ease of installation. Because all of the layers are molded in a single piece, you wrap the room once, not multiple times as you would for a traditional installation.

To make layout and installation much easier, some synthetic-molding manufacturers offer transition blocks for crown molding. Typically used in corners or in the middle of a long run (kind of like keystones in an arched door head), transition blocks require only square cuts — no more upside-down-and-backward angle cuts. They are a great DIY option, and they save installation time for contractors as well.

Entry doors often have combined molding packages: a grouping of plinth blocks, fluted casing and a head detail such as a pediment (which is often a combination of crown and 1x, among other things.) When made with wood moldings, this look requires a lot of pieces and a lot of layout. But synthetic moldings enable you to get same look with an easier-to-install three-piece package (photo, below).

PVC is a great paint-grade exterior door trim. It is not only durable but also easy to layer for a custom look. We ripped and routed basic 1x for this doorframe, and it turned out great.

The look of timber can add a lot of aesthetic appeal to a home, but milling an actual 8x8 is a specialized skill (and timbers are really heavy). Synthetic alternatives (photo, below) allow you to easily install lightweight yet rigid “timbers” in a country kitchen, build a rugged shelf in your man cave (for all of your trophies) or add a rustic mantel to your fi replace.

Faux timbers come in various sizes and in smooth (and primed for paint) or wood-grain textures (which can be stained or painted) to suit the scale and style of your home. They’re easier to mill, lift and install than wood.

Although it’s hard to beat the look of natural wood for a bead-board detail, PVC bead board works great for paint-grade projects. The Fypon PVC bead board we’ve used is 1/2 in. thick instead of the typical 3/4 in. for wood or 1/4 to 3/8 in. for medium-density fiberboard. This means that top-cap details can be what we call “right-sized.” (It may sound persnickety, but that extra 1/4 in. makes a difference.) What’s more, when we nail an edge, cut out for electrical boxes or make tiny rips at transitions, the pieces don’t break or split as wood and MDF sometimes do (photo, below).

Unlike wood molding, synthetics don’t split when you’re nailing at the ends, which makes them ideal for door casings.

PVC bead board or urethane base moldings are ideal materials to use around a raised tub or adjacent to a shower, especially in bathrooms using universal design elements such as zero-clearance (or wheel-in) features. Exposure to moisture and the minerals in hard water causes paint to peel off of bathroom woodwork in about five years — especially if you have kids. But PVC is pretty much immune to water damage and needs only one coat of paint. In fact, we used PVC to make “downspout pots” (see “Creative Uses for Synthetic Trim,” below) that get drenched with the water during storms. They easily survive not only the water but also being whipped with the string trimmer.

Creative Uses for Synthetic Trim

You can use synthetic moldings (and your imagination) to make all kinds of projects. For example, we made this little shelf (A) from a crown cutoff and a piece of PVC 1x. We also created custom containers (B) to catch water from downspouts — rainwater gurgles over instead of jetting into the grass. We even made a cat-food dish holder (C) out of a few pieces of crown topped with some routed 1x. It’s spray painted and easy to keep clean (and nicer to look at than a bunch of cat dishes on the floor).

Working With Synthetics
Although synthetic trim is visually similar to wood, there are a few special considerations to keep in mind as you work with it:

  • You can cope urethane and PVC with a coping saw at least as easily as wood. (We’re big fans of coping inside corners on molding projects. Our mantra is “Dead-end left; cope right.”) We’ve also coped PVC with a Dremel rotary tool. It takes a little practice, but it works great and is easier than using a saw. (Note: Coping does not work for all molding profiles.)
  • Synthetic molding comes already primed, and because of its exacting surface uniformity, impermeability and inertness to weather and moisture, only one coat of paint is required, even for exterior applications. Over time, synthetic molding suffers more from exposure to sunlight than from rain or temperature extremes.
  • Large amounts of synthetic sawdust can choke grass. For big jobs, set up your work area on a driveway or other nonorganic area (photo, below). At the very least, set up a drop cloth to catch the debris. (Note: We’ve seen wood sawdust choke grass too, but synthetics are more problematic.) Another good approach is to use a leaf vacuum to clean up. Be sure to contain the dust rather than blow it away.

    Synthetic sawdust doesn’t decompose, and lots of it can choke out grass. The fix is easy: Work on a driveway or patio, or set out sheets of plywood or a drop cloth; then vacuum (don’t blow away) the debris at the end of the day.

  • Although infeed/outfeed support is recommended for any project, urethane and PVC materials really need it. Because synthetic moldings are less rigid than their wood counterparts, it’s more difficult to get them to lie flat on a miter or table saw. Use infeed and outfeed supports for safe, accurate cutting.

For those of us who love wood moldings and trim details, switching to synthetic materials can feel almost like a betrayal. But throughout the history of houses, builders have used alternatives to wood: Moldings in many older homes were site-installed plaster (imagine that), and MDF has been very widely used for years. Urethane and PVC moldings are simply part of the evolution of building materials, and they have some distinct advantages. The process is a little different, but the results are what matter.