Composite & Plastic Decking

In this Article
Wood-Plastic Composites
Durability
Capped Composites
All Plastic Decking
Maintenance
Warranties
Choosing a Product
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A vast array of composite and plastic decking options promise wood-like appearance with minimal maintenance.

A vast array of composite and plastic decking options promise wood-like appearance with minimal maintenance.

Almost half of new decks now use composite  or plastic decking and the number continues to grow. The driving force is the promise of a wood-like appearance with minimal maintenance. How well each product lives up to this promise varies. There have been a few notable failures – composite products that rotted, for example, and were taken off the market. But, for the most part, these products perform well and require only a periodic cleaning to look, at-a-glance, like real wood decking.

Most products fall into the few categories discussed below, but each has unique characteristics and installation requirements. In all cases, review the product specs and, if possible, look at an installation before purchasing.

Composite Decking: What is it?

Decking materials made from finely ground wood fiber mixed with polymer resin have been in use for almost two decades. With a few notable exceptions, they have generally established a good track record. Many use a high percentage of recycled materials making them appealing to green building advocates. Most have a solid interior and are sold in sizes that match and install like standard wood decking. Others are extruded with hollow cores, which reduce weight and add stiffness, but require special trim pieces to hide the open ends.

In general, composite decking materials are dimen­sionally stable, resistant to the elements, and can be worked and installed more or less like wood decking. Special screws designed for composite decking leave a clean hole without dimpling around the screw head. Most solid products cannot exceed 16-inch on-center framing, and they feel a little bouncy underfoot due to the material’s greater flexibility (low modulus of elasticity) compared to wood.

Some products have an embossed wood-grain finish that may wear away over time. The colors also tend to fade over time and the surface texture roughen, giving an appearance similar to weathered wood. For some customers, this is fine; others who expect the decking to look new forever may be disappointed.

Many of the problems faced by first-generation products have been reduced with newer formulations. Two trends in particular – adding a plastic skin to composites and offering all-plastic options – have brought the industry closer to delivering on the promise of a “maintenance-free” wood-like decking.

Durability of Composite Decking

Geodeck composite decking was recalled in 2005 after widespread failures linked to rapid oxidation. The manufacturer subsequently closed it doors.

Geodeck composite decking was recalled in 2005 after widespread failures linked to rapid oxidation. The manufacturer subsequently closed it doors.

A combination of overzealous marketing by manufacturers and wishful thinking by homeowners created unrealistic expectations when composites were first introduced. Many customers thought they were getting a zero-maintenance product that would last forever. Within a few years, homeowners discovered that composites weathered under sunlight, got stained by cooking oil or tree sap, and could grow mildew or mold if left under a pile of wet leaves.

In some cases, products failed altogether as the composite chemistry failed to hold together or the wood fibers in some products absorbed water and rotted. Class-action lawsuits have been filed against Fiberon, Trex,  TimberTech, Azek (plastic decking) and just about all major manufacturers for fading, color change, mold growth, surface deterioration, and  in some cases structural decay. Even when mixed together with plastic, wood fiber still acts like wood.

In response, manufacturers toned down their marketing and  stepped up their maintenance instructions – recommending regular cleaning with a composite deck wash. They also modified their formulations to improve performance and durability. One of the challenges for manufacturers is that their raw materials – essentially sweepings from the lumber mill floor and (at least partially) recycled plastics is highly variable, so the products they output are variable. Some batches did not turn out so well, resulting in sporadic product failures. How widespread any given problem was is hard to determine as most of the lawsuits are settled out of court and are not public record.

Many factors affect the long-term performance of wood-plastic composites including the wood/plastic ratio, wood species and fiber size, the type of plastic resin and whether it is new or recycled. The manufacturing process also affects the surface characteristics and water absorption, which is critical to long-term resistance to mold and decay.

Chemical additives also play a big role. The quality and quantity of the pigments used for color affect fading resistance. And  proprietary additives and stabilizers are used  make the products stiffer and more resistant to UV radiation, crumbling, and mildew growth. High-quality ingredients and additives add a lot of cost to the formulations, so manufacturers must make choices of cost vs. performance.

On the plus side, these products have been sold for nearly 20 years and have definitely improved over that time. Despite sporadic problems, most composite decks have performed quite well, especially if the owner has done the basic maintenance of removing piles of wet leaves and debris, wiped up spills, and done a periodic cleaning with a deck wash.

Capped Composites

To address customers’ concerns, many manufacturers have introduced a new generation products that wrap the composite core with a “capstock,” – a tough plastic veneer about 1/16 in. thick made of PVC or proprietary plastics. Capped composites are the fastest growing segment of the composite decking market, referred to by some as “ultra-low maintenance.”

TimberTech's premium capped composites like this Tigerwood lookalike emulate tropical hardwoods.

TimberTech’s premium capped composites like this Tigerwood decking emulate tropical hardwoods. Photo courtesy of TimberTech

In addition to keeping moisture away from the wood fibers, the covering allowed more appealing (to some) faux-wood finishes and, more importantly, a more durable, easy-to-clean surface that is less prone to fade, scratch, or stain, or to support mold and mildew.

The best embossed wood-grain finishes look pretty realistic, much like Pergo flooring. Some companies encapsulate the core on all sides, some just the top, and some everywhere except the installation slots. In all products, the ends are exposed allowing limited moisture penetration at those points. Not surprisingly, each manufacturer claims that its particular capstock configuration is best but there is little data to support these claims.

The capped products are more expensive than standard composites and tend to carry longer warranties, usually with a number of important limitations. Since these products are fairly new and the capstock material is in some cases a company secret, it’s best to find one that has at least a few years under its belt – and to read the warranty carefully. Capped composites might turn out to be the killer app of composite decking, but it’s just too soon to tell. Also how well the faux-wood finish holds up to the elements over time is unclear.

All-Plastic Decking

Azek's all-plastic decking is unaffected by water. Its premium tropical hardwood line does a convincing imitation of the real thing in color and texture. Photo by author.

Azek’s all-plastic decking is unaffected by water. Its premium tropical hardwood line does a convincing imitation of the real thing in color and texture.

Another popular approach to ultra-low maintenance decking is to eliminate those pesky wood fibers altogether with 100% plastic decking. The growth of PVC decking has been driven, in large part, by the widespread popularity of Azek and other cellular PVC products now widely used for exterior trim. In fact, the decking is essentially the same as Azek trimboards, but with a tougher skin. Together with capped composites, solid PVC decking now accounts for nearly half the new residential decking market. Other large manufacturers of cellular PVC decking include Gossen and Wolf Home Products.

Less common,  one-of-a-kind types of plastic decking include BearBoard (HDPE), NyloBoard (recycled carpet fiber, and Eon (polystyrene, Canada only).

Older versions of PVC decking were made from hollow extrusions similar in profile to a vinyl window frame. Most products now have a solid core of cellular PVC encapsulated in a harder “capstock” skin similar to capped composites.

Because there is no wood fiber, PVC decking is immune to wood-related problems such as mold and wood decay. As with capped composites, the hardened outer skin provides color and realistic wood-grain textures, along with resistance to staining, fading, and scratching.

Resistance, however, does not mean the material is indestructible. Plastic can be scratched by heavy furniture or stained by oil or red wine that is left to bake in the sun. Also, some fading can be expected occur over time, especially with darker finishes. Azek refers to this as “weathering” not “fading,” but the result is the same. There are renewal products on the market that can restore a new look.

Like PVC trim, PVC decking cuts, drills, and installs more-or-less like wood. Despite the significant thermal expansion that can occur in unrestrained boards,  Azek recommends butting end joint tight. If you follow their installation instructions for either face-screwing or hidden fasteners, the thermal expansion will be restrained and the deck surface will remain dimensionally stable, according to the manufacturer.

Hot Feet.  All decking products can get hot underfoot with a direct overhead sun exposure, but plastic and composite decking have a reputation for getting uncomfortably hot in warm, sunny climates. In general the darker the color and the denser the material, the hotter the material will get in full sunshine. If that’s a concern, a simple comparison of competing products laid out in the sun is the best way to go. The same goes for dark wood decking when the original dark color is maintained.

Maintenance of Composite & Plastic Decking

With so many products, you can now find synthetic and composite deck boards  in almost any natural or stained wood color and with a smooth surface or realistic embossed grain pattern. The big question is not so much what the product looks like in the showroom, but what will it look like 3, 5, and 10 years later after exposure to the sunlight, foot traffic, tree sap, and food and wine spills. The answer depends on the specific product, exposure to sunlight, wear and tear, and user maintenance.

To their credit, synthetic decks require much less maintenance than wood decking. No sealers, stains, or sanding will ever be required. With standard composites, once the surface weathers, it bears a strong resem­blance to weathered wood, but without the customary warping and checking. Capped products should retain their color and surface texture with normal wear and exposure.

To prevent mildew growth, standard composites need to be keep free of leaves and debris and washed periodically with a composite deck wash. For capped products (composite or PVC) a gentle soap and water wash is adequate. For all synthetic decks, oil and grease, red wine, and other substances prone to staining should be removed with warm soapy water along with a soft brush for embossed patterns. For other stains and general maintenance requirements, make sure to read the manufacturer’s recommendations or you risk voiding your warranty.

Warranties for Synthetic Decking

I take all building material warranties with a large grain, or shovel-full, or salt. They generally cover only materials, not labor, and are often prorated for years in service. And there are enough technicalities and limitations that the manufacturer can always claim that you didn’t follow some aspect of the installation instructions.

That said, a stronger warranty from a reputable company is worth more than a weak warranty from a fly-by-night or out-of-business firm. Because of the relatively high failure rate of decking products it’s foolish not  to read the warranty and supporting documents. In addition to installation details such as maximum spans and fasteners, limitations may apply to types of cleaners and chemicals used, how fast you remove stains, ventilation space below the decking, clearance to the ground, treatment of ends, and maintenance requirements, such as “no abrasive cleaners or metal-edged snow shovels…”

Since most warranties are voided for things like “improper installation, or failure to abide by Manufacturers’ guidelines” for such things as handling, storage, and maintenance, you will need to do a little detective work to find out what those guidelines are. If it’s unclear call or email the manufacturer. You can usually find this additional information on the manufacturer’s website, although sometimes in different places: Installation Instructions, FAQs, Cleaning & Maintenance, etc. If you don’t find what you’re looking for, by all means call or email the manufacturer.

Here’s a limitation from Azek, somewhat illogically covered under “Care and Cleaning,”  that you probably never thought of:

“Sunlight, which may be reflected by low-emissivity (Low-E) glass, can potentially lead to damage of exterior building products, including AZEK Deck…products, due to elevation of surface temperatures which far exceed that of normal exposure of the same materials to direct sunlight. Possible damage by such reflected concentrated light may include melting, sagging, warping, distortion, surface discoloration, increased expansion or contraction, and unusual weathering.”

Look for products with the longest warranties with the fewest limitations. Limited warranties on the best products are often 20 to 25 years. In wet climates or applications, look for products rated for use in ground contact or close to the ground as these will likely be the most impervious to moisture damage. Above all else, look for a reputable manufacturer who has a reputation for standing behind its products. Contractors’ lumberyards are a good resource here.

Choosing the Right One

Synthetic and composite decking offers a bewildering array of products – some with a decent track record, some brand new, and most made using a proprietary recipe and manufacturing process. Visit a contractor lumberyard that carries several lines. Look at lots of samples to see what appeals to you. Some look like plastic; some you couldn’t tell from real wood when viewed from a foot away.

Ask the lumberyard which products hold up the best for the application you are planning. Take home some samples. Try to scratch them with keys, stain them with cooking oil, red wine, and permanent markers, and then try to clean them. These quick-and-dirty tests can tell you a lot about real world performance, at least in the short run. If you’re in no rush, leave a few samples out for several months to see how they fare when exposed to the elements.

Products are constantly changing and small manufacturers come and go. With composites, many technical factors involving materials and manufacturing are difficult or impossible to know or evaluate – the percentage of wood vs. polyurethane, particle sizes, additives, and cap materials, among others. Since it’s hard to know exactly what you are buying, you are really banking on a manufacturer that you can trust is putting out a quality product and will be around to honor the warranty if there is a problem.

While some of the largest manufacturers, such as Trex, Fiberon, and TimberTech have had high-profile failures, they have also been around the longest, have made huge investments into R&D, and are most likely to be around in the future. Along with other industry leaders such as TimberTech, Azek, and Gossen these companies have the most skin in the game and the strongest commitment to producing high quality products and supporting them. Especially avoid home-center brands as they are sourced from different manufacturers and you have no idea what you are getting.

Finally, don’t expect miracles – and buy enough extra stock to repair the occasional damaged board in the future. You can’t just sand and refinish a bad ding, or buy a board at the local lumberyard in three years and expect it to match.

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Comments

  1. SD Galindo says:

    Best Composite Decking for Wet Climates?

    I’m doing a very large deck in the pacific northwest – lots of potential for mold, mildew, and water damage. I’ve looked mostly at capped composites with recycled content. I eliminated Trex because it is only capped on 3 sides. I eliminated Azek because it isn’t reversible. Fiberon is my top pick so far though I’d love to find a product sealed on 6 sides, and I’m considering California Bamboo if available up here. You mentioned looking for ground-rated products for best moisture resistance in wetter areas (like the pacific northwest). I haven’t seen anyone mention ground-rated decking. Can you name a few brands?

    • buildingadvisor says:

      The only wood-plastic composite decking I know that is specifically rated for ground-contact is MoistureShield (sold as Modern View decking) in some markets) claims that their decking can be installed “on or in the ground or underwater without voiding the warranty” – a pretty bold claim.

      Most composites rated for contact with ground and water do not have any wood content. These materials are have high plastic content with some mineral or other inorganic filler. Bear Board “plastic lumber” is about 50% HDPE (high-density polyethylene) and is sold for use as pool decks and marine docks. This

      The other option, which you mentioned, is PVC decking such as Azek and Gossen, which are both 100% cellular PVC with a capstock.

      Gossen states that its products can be used “ in high moisture areas and…is perfect near water. Whether you use it next to fresh water, salt water or chlorinated pool water, the surface of the boards will stay fresh looking — even in the highest traffic areas. Gossen decking will not rot, warp, split, fade or mold.” However, its installation instructions specify a minimum of 6 in. clearance to the ground for ventilation of heat and moisture. They seem to be hedging their bets.

      Azek makes similar claims about use near water, but does provide details for use on sleepers, such as rooftop decks, and on deck joists at grade. They don’t specifically mention ground contact one way or the other.

      You specific concerns are mold, mildew, and water damage. Mold and mildew can grow on virtually any surface that is allowed to stay wet in warm weather. So if you leave a pile of leaf debris on any deck, you can expect some mold growth and staining as well from the tannins. The best protection is regular maintenance and periodic cleaning. Every manufacturer of composite and plastic decking publishes cleaning instructions, which are worth reading and following.

      Deterioration of the decking material from moisture is more a function of the material and climate. The premium capped composites should probably perform well for you, but if you want the best protection from moisture, a product with no wood fiber might be a better choice. If you are concerned about moisture exposure at end cuts, you can seal the ends with the same sealers used on hardwood decking, such as Ipe Seal or specialty sealers such as TimberTech End Coating.

      The appearance over time should also be considered. Some fading, scratching, and weathering will occur, especially under full sun exposure. If possible, take a look at 5-10 year old deck with the material you are considering.

      It is always difficult to estimating the longevity of composite and plastic decking. Few composite products have been out long enough to establish a long track record and formulas change frequently, often in response to problems in the field. There have been a number of notable product failures and more than a few class-action lawsuits. Also how you install and maintain the decking plays a role in how long it lasts.

      A long warranty is one indicator of a manufacturer’s confidence in a product, but not the same thing as proven performance in the field. In practice, building product warranties usually aren’t worth much unless you are working with a well-established manufacturer who stands behind their product. Many are for materials only, are prorated, and can be easily voided by “installation errors.”

      You might also consider tropical hardwood decking. If you don’t mind letting it weather to a silver gray, it can perform as well as the best composites and require a similar amount of maintenance. Plus if it gets really ratty, you can always sand and refinish!

      • SD Galindo says:

        Thank you for the detailed helpful reply! I do not wish to support tropical hardwood industry and my house is rented right now (though I plan to retire there, I’m working out of state) so I cannot assure proper maintenance of wood (sealing annually, let alone cleaning frequently).

        It will be at least 30″ off the ground but I live in a very wet area with lots of plant debris. The mildew/mold occurs from moisture – even on my covered deck – whether or not there is debris. I have used a bleach solution to get rid of it – and I read this is ok for the capped composites.

        Thus, as an absent landlord, the capped composites with sealed ends or PVC seem to be a better option. I was a bit shocked at the price.

        I did review Moisture Shield – it is 95% recycled, and reversible with a ‘lifetime transferable warranty’, and Fiberon is capped on 4 sides, 25 year warranty.

        I will read the warranties more carefully… so far Moisture Shield and Fiberon are my top choices. Also considering Calibamboo.

        Do you have any thoughts on bamboo?

        kind regards, LM

        • buildingadvisor says:

          Sounds like you’ve done your homework and have identified some of the top-performing products (unfortunately with the top prices as well). Since you will likely get debris, mold, mildew growth on any deck under those conditions, you will want something that is relatively easy to clean. Each product publishes cleaning instructions, some recommending specific cleaners and types of brushes and prohibiting others that are too abrasive for the material.

          I’m a big fan of testing materials. Buy a sample piece of the two or three materials you are considering and test them for cleaning. If you don’t have time to grow mold, use permanent markers to simulate stains, and other sticky substances such as roofing tar to simulate tree sap and grime. You can get pretty creative here.

          Then see how quickly each cleans and whether you can remove all the stains. I have used this type of testing on flooring, plastic laminate, and other materials and have found it a good predictor of performance in the field.

          I am not familiar with Calimbamboo and don’t think it is distributed here in the Northeast.

          Another high-end product you might consider is aluminum decking such as Versadeck or LockDry. These should last as long or longer than any decking material and require minimal upkeep. But, as you note, no decking is truly maintenance-free.

          Best of luck!

  2. Joseph Fitzpatrick says:

    Any Feedback on Lang Composite Decking

    Has any one used lang composite deck boards and your thoughts good or bad?

    • buildingadvisor says:

      I’d be interested to hear from other readers on their experience with composite decking?

      Lang is a discount brand and not a major player in composite decking. While they may offer a 25-year residential warranty, there is little reason to believe that the product or company will be around in 25 years as smaller composite decking manufacturers come and go frequently. Some no-name manufacturers do not turn out a consistent product, so one batch may differ a lot from the next.

      Also, the industry has been plagued by a number of high-profile product failures over the years. It’s not easy to manufacture a premium composite that will deliver long-term performance. So it may be penny-wise and pound foolish to try to save a few hundred dollars on materials by going with little known discount product.

      Material prices for composite decking range from $3 to $4/sq.ft. at the low end to $7 to $8/sq.ft. or more at the high end. Issues to consider, in addition to overall durability, are resistance to UV, scratches, stains, and mildew. Best to choose a manufacturer who has a strong track record and who stands behind their product.

  3. Composite vs. PVC Decking

    Hello,
    What’s your opinion of Wolf composite decking? We’re also considering Wolf PVC but might be cost prohibitive. Thank you

    • buildingadvisor says:

      Wolf is one of the country’s largest suppliers of kitchen cabinets. They got into the composite decking business in 2010 and have become a major supplier of cellular PVC decking, second only to Azek. Both companies have a good reputation and a good track record with PVC decking despite some problems Azek had with earlier formulations.

      I have not used Wolf’s composite decking products, but know that they are part of the new generation of composite decking products with a hard plastic skin or “capstock” over a composite core. These tend to wear better and are less prone to scratch and stain than standard composite decking. It’s not clear from the company’s literature what the capstock material is. Other manufacturers use pvc, polyethylene, ASA and other “proprietary” plastics as the capstock.

      Capstock products were developed, in part, to address issues with staining, fading, and surface deterioration with some of the traditional composite decking products such as Trex. They offer more variety of grain and color, but like other simulated wood finishes, some look more authentic than others.

      The only problem I have heard about capstock decking is swelling of the ends, which are exposed to weather – similar to the swelling of OSB edges. To avoid this problem, some installers recommend sealing the ends of capstock decking with an end-grain sealer or water-repellent preservative (WRP).

      Ask the supplier or contractor if they can show you a deck that’s at least five years old with this type of decking. That’s the best predictor of wear characteristics and durability over time.

  4. I have a wood-framed base and want to install composite decking on it, using a 12 ft. middle support. What spacing between the joists is required to support the composite decking?

    • buildingadvisor says:

      Each composite decking product is different, so you need to check with the manufacturer of the specific product (or the supplier) about span requirements. In most cases, you can find product specifications online, but not always with home-center brands — not a good bet with composite decking.

      In general, composite decking is less stiff than solid wood making it a little more bouncy and prone to sagging. Allowable spans range from 12 in. to 20 in. A few claim that they can span 24 in. but I would be skeptical. It depends, in part, on how much bounciness you are willing to tolerate in a deck.

      Remember that the published allowable span number is the maximum. So you may want the spacing a little less if a solid feel is important to you. So, for example, if it says 20 in., 16 in. would be better. If it says 24 in., 16 would be better.

      You can conduct a simple test by attaching a few decking boards across to some 2x4s set on edge. Then step on the flooring sample to see if it feels solid enough for you.

      Good luck with your deck project!

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