Recently, one of my deck clients showed me some samples from a local decking supplier. There were a couple of composites, a new-generation capped composite, and some ipe and tigerwood. When I asked which she thought were the prettiest, she quickly pointed to the wood samples. When I asked her opinion of the capped composite, she said, "It looks like it's got shiny paint on it." Citing the benefits of the capping had little effect on her, so it seems that the quest for the perfect substitute for wood continues.
Manufacturers have made great efforts to earn top scores in looks while producing durable planks that will last decades with few signs of age. Early synthetics fell short of these goals. Some bore little resemblance to real wood; some faded and stained; some fell apart. While today's synthetics are vastly superior to their predecessors, comparing synthetic decking products can make your head swim. It would be convenient if all synthetic decking products were created equal and the only variable was looks. Then making a recommendation would be a cinch: Just hold a beauty contest and install the winner. But synthetics are like restaurants: Each has its own guarded recipes and a unique d©cor.
Recipes for Synthetic Decking
Although a few nonwood deck products contain little or no plastic - such as aluminum deck systems, stone deck tiles, and Rumber boards (made of rubber from recycled tires) - almost all formulas for synthetic decking are rich with polyethylene (HDPE or LDPE) or PVC (polyvinyl chloride).
In the past, some North American composite makers used polyurethane, polypropylene, or PVC as their plastic. Now, they mix polyethylene with reinforcing ingredients such as wood flour, ground rice hulls, fibers, or minerals, as well as some chemical additives.
Battling the composites for market share are all-plastic decking products extruded from PVC in either a foamed structure known as "cellular" or a nonfoamed, noncellular structure that is confusingly referred to as "solid PVC," "hollow PVC," or just "vinyl decking." Cellular PVC is the relative newcomer in the all-plastic sector, outselling vinyl decking ancestors by providing the woodlike sound and appearance that homeowners desire and the workability of wood that installers appreciate. (Eon, an all-plastic decking made from polystyrene by Ontario's Gracious Living Corp., once competed in the U.S. but now is marketed solely in Canada.)
Except for EverGrain, which is made using compression molding, each deck product mentioned in this article is made by forcing a hot mixture of materials through a heated die that forms the decking's shape. Mono-extrusion, the process used for the early generations of WPCs, is still used today. In mono-extrusion, the raw mixture forms a single layer of material after passing through the die, with the mix of components evenly distributed throughout the entire cross section of the board. The uniform consistency of the composite material is evident when you look at the end of a sample.
Mono-extrusion is used for some cellular PVC deck boards as well. The lightweight core is a tightly-packed structure of miniscule bubbles locked into the cured PVC foam. There are two different methods of foaming: free foam and Celuka. The Celuka process provides a harder outer skin than free foaming. As Shane O'Neill with Compositology puts it: "Free-foaming does form a skin, just not a thick, hardened armor exterior. There are pros and cons associated with Celuka. While it is stronger and tougher, it may be susceptible to chipping or fastener surface cracks, because the outside is so tough and rigid while the core is softer."
Co-extrusion is a dual-layer extruding process that enables an outer layer called a capstock to be fused to an inner substrate under heat and pressure. On composites, the capstock is a chemical mixture engineered to keep the core from absorbing moisture while also boosting stain, mildew, scratch, and fade resistance. It also allows for increased color choices, including variegated tones and shading. With PVC decking, the capstock layer is primarily used to impart multishaded and darker colors, which are difficult to deliver with mono-extrusion.
The Composite Players
Whether they co-extrude with a capstock or not, composite makers distinguish themselves from the rest of the pack in a variety of ways. Tamko, maker of EverGrain, applies one of the deepest wood-grain textures in the industry. Accents, the starter composite in the Trex family, also has a grain pattern, of prominent repeating cathedral arches ("plain-sawn" or "flat-grained" in the wood world), on one side.
Some makers put a wood-grain texture on both sides of the boards so they are reversible (Figure 1). A.E.R.T.'s MoistureShield wood-plastic-composite deck boards get a wood-grain pattern on both sides during the extrusion process. The same is true for CertainTeed's EverNew 20 composite and Fiberon's Professional Decking - both are made by Fiberon and offered as the least expensive composite in each company's lineup.
Figure 1. Many composite decking boards have a grain pattern on both sides so they are reversible
Other boards are reversible but have a different texture on each side. TimberTech's TwinFinish Plank has a "vertigrain" wood pattern with long, wavy grains embossed on its walking side and a "serrated" texture, akin to extra-narrow wale corduroy fabric, on the flip side for use on benches, flower boxes, and other deck accents. UltraDeck Rustic by Midwest Manufacturing has a "plowed" side (with a finely-grooved texture like TimberTech's "serrated" finish) and a wood-grained side. Unlike most composites, all three lines from Midwest Manufacturing are extruded with hollow profiles, saving material. Internal ribs between the cores, acting like the flanges of steel beams, add strength. Intrepid, the entry-level composite in the Latitudes lineup offered by Universal Forest Products, comes in four colors and has wood-graining on one side and a subtle brushed texture on the other.
Cali Bamboo's BamDeck composite planks are also reversible, with one side having a very fine linear texture similar to the grain of brushed metal, while the other side is deeply grooved for extra traction and visual distinction. This can be a safety feature for steps, and a fun feature for creating a different look (Figure 2). Cali Bamboo is the only maker using bamboo fibers and is one of the few that does not try to make its products look like wood. With slotted edges, each plank is installed with hidden fasteners, an option with all composites.
Figure 2. BamDeck offers a deeply grooved face to provide better traction and a visual clue for stair treads.
Wisconsin's Green Bay Decking is one of several composite makers that eschew wood flour because of its water-absorption properties; instead it mixes ground rice hulls and processed paper sludge with virgin HDPE to make GeoDeck planks (Figure 3). GeoDeck is a rare example of an extruded composite with a hollow core. Matching perimeter strips are used at deck edges to hide the open cores from view. Terratec Naturals by McFarland Cascade is another product made with ground rice hulls. The high silica content of the hulls imparts natural stain and moisture resistance to the decking, according to the manufacturer.
Figure 3. GeoDeck is a rare hollow composite decking, and it uses rice hulls and waste paper fiber rather than wood flour.
Natures Composites takes a different route, relying on wheat fibers in its TerraDeck composite recipe. Based in Torrington, Wyo., Natures Composites takes advantage of the local abundance of straw, a byproduct of harvesting wheat. According to Kim Boos, the national sales and marketing manager for the company, wheat-straw fiber is stronger than wood cellulose, absorbs less water, and contains no proteins or starches, which can act as a food source for mold.
Other composites touting no wood ingredients are Bear Board, EnduraBoard, and NyloDeck. The first, by Engineered Plastic Systems, is made from at least 50 percent recycled HDPE and reinforced with a secret blend of minerals (essentially pulverized rock, according to Rob Stevenson of the company). The manufacturer claims that minerals in Bear Board and its twin product Lumberock add strength, increase durability, and decrease expansion and contraction. Crawford Industries' EnduraBoard has a similar composition: mostly recycled HDPE plus about 40 percent minerals. NyloDeck, by Georgia-based Nyloboard, distinguishes itself from other composites by using 100 percent post-consumer recycled nylon carpet fibers mixed with a proprietary resin (Figure 4).
Figure 4. NyloBoard decking is a composite of recycled carpet fiber and plastic resin.