We first began installing cellular PVC trim on our projects in 2005, using it for outer band trim, rail caps, bar tops, skirting, and amenity trim. When we began to focus on porches, we used it for wrapped columns and beams, sill plate wraps, and chair-rail, along with traditional uses like fascia, soffits, and corner and frieze boards. Over the years, we've found a number of other applications, including built-in weatherproof benches and outdoor cabinets.
If you’re not using PVC trim on your own projects, you’re missing out. Not only is it a product that will reduce callbacks and warranty claims, it will also help you differentiate yourself from your competitors and increase your bottom line.
The Same, but Different
Each company that offers cellular PVC trim manufactures it slightly differently, with different additives and processes. Sometimes these differences—in whiteness or texture, for instance—are noticeable simply by comparing boards. There are also less-visible variables: levels of UV protection, degrees of thermal expansion and contraction, and capacities for paint adhesion. And guaranteed exact measurement tolerances can vary from one manufacturer to another by 1/32 inch or more. All of these characteristics affect the performance of the trim, so it pays to shop carefully.
Depending on the manufacturer, PVC trim is available in a wide range of sizes, including 1x4 and 1x6 boards in 12- and 18-foot lengths and 4x8 sheets, and at least one manufacturer (Versatex) offers 4-foot-wide sheets up to 20 to 24 feet long in a number of thicknesses. Two-by material, a good option for arbors and even railings, is also available, in typical nominal sizes from 2x4 through 2x12. Numerous profiles are now available too.
When I first started using PVC trim, I unfortunately didn’t pay too much attention to the manufacturer’s installation instructions, and I had some callback issues. What I quickly found out is that PVC trim isn’t installed or finished exactly the same way as wood trim. For example, one of our biggest early mistakes was to install PVC rail caps with butt joints held in place with pairs of screws at the joints. Since PVC expands and contracts with changes in temperature, these joints would then open up and allow water to soak into the wood below, causing the wood to swell and the joint to open up even more. In a few cases, the movement stressed the joint enough to break the fasteners.
Read the Installation Instructions
For cutting, most manufacturers recommend using carbide-tipped blades with as few teeth as possible. That’s because more teeth leads to more frictional heat build-up in the cut, which can melt or even possibly burn the PVC. We’ve found that blades with a 32- to 40-tooth count work fine. PVC trim flexes more than wood, so it’s a good idea to have plenty of support on both sides of your cutting station.
Spraying static guard on our tools and even on ourselves helps to keep most of the PVC dust from clinging to and clogging tools. If you’re working inside a shop, it’s a good idea to hook up your cutting tools to some kind of dust collection system. When you're working outdoors, a little planning—such as using a drop cloth to catch the shavings—is helpful for job cleanup if you’re not in an area that can be easily swept up.
PVC trim can be installed with nails, screws, and plug systems, typically with the fasteners spaced 16 inches on-center. As a general rule of thumb, we use two fasteners every 16 inches for 1x4s and 1x6s, three for 1x8s and 1x10s, and three to four for a 1x12, but it’s always best to refer to the manufacturer’s installation guidelines.
We prefer to use stainless steel rather than galvanized fasteners, sized so that at least 1 1/4 inches of the fastener penetrates into the substrate. While thin-gauge staples are not recommended for use with PVC trim, we sometimes use stainless steel finish nails along with PVC glue to make the running edge connections when building custom column wraps. Of course, some manufacturers now offer prefabricated column wrap kits that install easily without the labor needed for custom columns. In most cases, no nails are needed either, since there is typically a single running joint that only requires glue.
For hand-nailing fascia and outer band trim that is going to be painted, we use 8D SS ring-shank nails. Trim can also be installed with pneumatic finish nailers set to between 80 and 100 psi, depending on the thickness of the trim, the fastener gauge, and the type of gun. As a general guideline, if the fastener can be bent between your fingers, it’s not recommended.
For trim that’s not going to be painted, we use either trim screws with prepainted heads, such as GRK’s RT Composite screws, or one of the plugged screw systems, such as FastenMaster’s Cortex or Starborn's Pro Plug (available with stainless steel fasteners). When installing PVC rail cap, we fasten it to the substrate with either prefinished SS trim screws or 2 1/2- to 3-inch SS screws that are filled and painted over when trim paint is applied.
Thermal Expansion and Running Joints
When it’s hot outside, PVC trim expands; when the temperature drops, it contracts. The rate of expansion or contraction is about 1/16 inch per 20-degree change in temperature above or below the initial installation temperature. Any thermal movement that does occur will be along the length, rather than across the width, of the board and is more of a factor with longer lengths. PVC is not affected by moisture and does not swell like wood, as it doesn’t absorb water.
To avoid problems with running joints, we’ve learned to allow and compensate for thermal movement during installation. For example, during the summer, we try to run trim earlier in the day before it has had a chance to heat up. We also try to keep PVC stacked out of the sun prior to installation, rather than leaving the material out in the driveway all day.
When it’s hot, all joints should be tight. In cool or cold weather near freezing, we leave 1/8- to 1/4-inch gaps at joints to allow for the movement that will eventually occur when it warms up.
It is possible to create a PVC joint that won’t open up. To control movement at lapped butt joints—which I use when installing long runs of rail cap, outer band trim, or fascia—I employ a three-step process. First, I apply an outdoor construction adhesive (Versatex recommends Liquid Nails Heavy-Duty Construction Adhesive LN-903) to the back of both trim pieces, extending about 2 to 3 feet from each side of the butt joint. Then I fasten the first trim piece to the substrate with two pairs of fasteners, one pair an inch from the joint, and the next pair 2 inches behind the first.
Next, I apply PVC glue (Weld-On PVC 705 works well) to the end of one of the two pieces being butted together. (Applying glue to both ends will weaken the joint by not allowing the two pieces of PVC to fuse together properly). Finally, I install the second piece of trim like the first, with a double set of fasteners. With the joint locked together like this, any thermal movement will be forced to occur away from the joint.
With rail cap and outer bands on decks, it’s not likely that there will be more than a couple of full lengths of run at a time. Even so, I like to make an allowance for expansion somewhere along the length of the trim, either at a corner or with a shiplap movement joint at one of the butt joints (explained below). If the run is fairly short (less than 14 feet) then I lock down any joints with the three-step process.
When fascia or outer band trim is being installed from a 90-degree corner, I like to begin with a 6- to 8-foot-long starter piece. I use PVC glue in the joint itself, glue the trim to the substrate with construction adhesive, and use double fasteners to lock the corner in place using the method described above. Then I use the three-step attachment method with the next full length of trim, unless that’s where I plan to place a movement joint. Since shorter lengths typically don’t move much anyway, this approach helps insure that the corner joint won’t open up.
Where stair rail cap meets the flat rail, it’s better to let the flat cap extend out and overlap the sloped stair rail cap, rather than try to create a mitered joint. This allows the angled piece on the stairs to run underneath the upper cap, which hides any movement that might occur.
On gable fascia, I typically will install a chevron-shaped piece of decorative trim at the peak that hides the fascia joint and allows the two pieces of fascia to move.
Shiplap Movement Joints
When there are longer runs with three or more boards involved, I make sure that at least one of the joints is a movement joint to handle thermal expansion and contraction. Instead of the three-step butt joint, I make a shiplap joint using a small router with a rabbeting bit. After making the initial cut into the middle of the board end, I let the router bite in and then use a layout square as a guide to keep the router from running around the corners.
To allow for movement, I omit any adhesives and fasten the boards with single pairs of fasteners about an inch from the end of each board. Some builders fill their movement joints with a flexible sealant, but my feeling is that even if there is movement, there will still be material in the gap to block moisture from penetrating beneath the trim into the underlying substrate when it opens up. When possible, I try to locate shiplap expansion joints in the least visible areas.
Closing Up the Cells
Routing and ripping PVC opens up cells in the material, which can then trap dirt and debris. The same thing occurs on end cuts that are left exposed. To address this problem, I lightly hand-sand cut or routed edges with 320-grit sandpaper, and then wipe with a cloth soaked with acetone. The acetone chemically reacts with the open cells, heating them and closing them up.
If a long rip cut is involved, a palm sander with 320-grit paper speeds up the process. But keep in mind that the goal isn’t to sand the material until it’s closed up, but only to get the process started. It’s the acetone that does that work.
For normal cleanup (especially on PVC trim that isn’t going to be painted), we use CorteClean or even regular household cleaners such as Soft Scrub or Spic & Span. If there are stubborn stains, a nylon scrubbing pad can be helpful; so can careful handling and keeping the material covered to protect it from dirt and debris in the first place.
For hammer marks, band strap marks, or areas where the board was crushed or pushed in and the original material still exists, a heat gun held about a foot away from the ding can often pull or bake it back out. If it’s a deeper scratch or gouge where material has been removed, a structural adhesive filler such as two-part PVC TrimWelder will be required.
Urethane caulk must be used with PVC trim; silicone will not adhere properly. If the caulk tube doesn’t have a metal end cap, it’s likely the wrong caulk. If we’re using Versatex and aren’t planning on doing any painting, we use NPC’s Solar Seal 900 because it’s color-matched to this particular product, and it has a lot of elasticity.
If the trim is going to be painted and we’ve used nails instead of plugged screws, I like to fill the nail holes. Versatex recommends DAP CrackSHOT, but pretty much any good vinyl spackling product will do.
Some PVC manufacturers claim that priming their trim isn’t necessary; still, we always prime our trim prior to painting. And in some cases, PVC trim must be painted to prevent "yellowing." In all cases, again, it’s important to follow the manufacturer’s recommendations.
100% acrylic latex paint is recommended for use with Versatex, the brand of PVC we use most often. According to the company, standard paints—such as Sherwin-Williams’ Duration or Benjamin Moore’s Moorlife—are fine to use with its PVC trim, as long as the paint is a lighter color with a reflective value of at least 55. The "light reflective value" (LRV) can be found on the paint tabs in the paint store.
Dark paints can also be used with PVC trim, but they must be formulated specifically for this purpose. Specialty paints, such as Benjamin Moore’s Vinyl Select and Sherwin-Williams’ Vinyl Safe, that are made for vinyl siding are a little more expensive than standard paints because of their built-in reflective capacity, so plan on additional expense and consulting time with your paint store rep.
An Upgrade That Improves Your Bottom Line
I’ve since sold my Atlanta-area deck and porch company, but when I founded it, I created a short list of high-performance products that I wanted to incorporate as standard offerings to our clients. Cellular PVC trim was one of the products on that list, because I believed in its performance and felt that the value that it brought to a job was well worth the slight increase in cost (which will vary a lot depending on the project, the market, and local labor costs, especially if a screw-and-plug system is used).
Over the years, it proved to be easy to communicate that value to prospective customers, especially those who had dealt with repairs and maintenance issues in the past. In fact, one of the keys to my success as a contractor was using high-performing products such as cellular PVC trim, which did a good job of differentiating my company from my competitors.