Composite Decking: Know these Before Installing

Written By Adam Paul – Waterproofing Expert

Composite decking is an engineered outdoor surfacing material created from a blend of recycled plastics and wood fibers that improves moisture resistance, UV stability, and long-term structural reliability. Installing composite decking can increase the durability, reduce maintenance, improve water resistance, increase color retention, enhance slip resistance, and reduce the environmental impact of the deck. There are four mainly 4 types, such as capped composite, uncapped composite, PVC composite, and mineral-based composite.

The recommended thickness of composite decking is typically 25-38 mm (1-1.5 inches) for residential decks and 38-50 mm (1.5-2 inches) for commercial high traffic areas. Composite decking is eco-friendly. The cost for the composite decking varied with the surface area, material quality, labor rates, deck complexity, and additional features.

Composite decking absorbs UV light when it is exposed to UV radiation for a short period. But when it is exposed to a longer period, it causes color fading, surface chalking, thermal expansion, contraction gaps, heat retention, sheen loss, material softening, and increased surface slickness. To maintain a Composite decking, it should be properly maintained every 6-12 months. To install a composite decking, you should follow the steps recommended by the Aqviz experts. For the last long composite decking, it should be protected properly. Aqviz experts highly recommend that you should not waterproof the composite decking at any time. Instead, you should protect the structure properly.

What is Composite Decking?

Composite decking is an engineered outdoor surfacing material created from a blend of recycled plastics and wood fibers that improves moisture resistance, UV stability, and long-term structural reliability. Composite decking uses polyethylene, polypropylene, or PVC mixed with finely ground wood flour to form dense boards that resist swelling, rotting, and surface deterioration during exterior exposure.

Composite decking helps to reduce maintenance because the boards do not absorb water in the same way natural timber does, and the co-extruded outer shell provides consistent color and texture. Composite decking are mainly two types such as uncapped composites and capped composites, and each delivers different protection levels depending on the thickness and polymer composition.

Composite decking supports outdoor living areas with high durability and long-lasting aesthetic appeal. The minimum thickness of composite decking is 25 mm or 1 inch, which maintains stiffness under 120–150 lb loads and prevents mid-span deflection. If composite decking contacts water for a short period, the surface sheath blocks absorption and prevents grain raising or swelling.

If water remains trapped under the boards, moisture may infiltrate the core in uncapped products. It leads to early-stage mold stains. If composite decking remains under prolonged sunlight, the UV-stabilized cap reduces fading and surface chalking, although darker colors can reach 45-55°C on hot days. These behaviors help composite decking maintain predictable durability and consistent appearance across multi-season exposure.

What are the Benefits of Composite Decking?

There are 6 main benefits of composite decking, such as,

• Increase durability: Composite decking increases resistance to rot, decay, and insect damage compared to natural wood.
• Reduce maintenance: Composite decking reduces the need for sanding, staining, or sealing, saving time and cost over its lifespan.
• Improve water resistance: Composite decking improves resistance to moisture absorption, reducing warping, swelling, and surface cracking.
• Increase color retention: Composite decking increases long-term color stability and resists fading from UV exposure.
• Enhance slip resistance: Composite decking enhances safety by providing better traction on wet or damp surfaces.
• Reduce environmental impact: Composite decking reduces reliance on natural timber and often contains recycled materials, promoting sustainable construction.

What are the 4 Types of Composite Decking?

There are four mainly 4 types such as capped composite, uncapped composite, PVC composite, and mineral-based composite.

1. Capped composite decking uses a protective polymer shell that improves stain resistance and reduces water infiltration, making it stable during 30-50°C heat cycles.
2. Uncapped composite decking exposes the wood-fiber core, which increases water absorption and allows color fading under strong UV radiation.
3. PVC composite decking removes wood fibers completely and offers near-zero moisture uptake, which eliminates swelling during heavy rainfall.
4. Mineral-based composite decking blends minerals with polymers, increasing stiffness by 30-40 percent and reducing thermal expansion under prolonged sunlight exposure.

These types allow homeowners to choose the right balance of strength, longevity, and climate compatibility.

What is the Recommended Thickness of Composite Decking?

The recommended thickness of composite decking is typically 25-38 mm (1-1.5 inches) for residential decks. For commercial or high-traffic decks, a thickness of 38-50 mm (1.5-2 inches). These recommended thickness ensures structural strength, reduce deflection between joists, and support heavier loads safely.

Is Composite Decking Eco-Friendly?

Yes, composite decking is eco-friendly because it is made from a blend of recycled wood fibers and recycled plastics, which reduces the demand for virgin timber and diverts plastic waste from landfills. Composite decking increases sustainability by lasting longer than traditional wood, reducing the need for frequent replacement, and lowering the use of chemical stains, sealants, and preservatives that can harm the environment.

How much Does it Cost for Composite Decking?

Composite decking costs vary with material quality (basic to premium capped boards), labor rates, deck complexity, and additional features like railings or stairs. The average cost for the composite decking can vary as follow.

• Composite decking cost for square foot: $22-$65 (including all the expenses with materials)
• Composite deck cost for an average-sized deck: $5000-$12000 (including all the expenses with materials)
• Composite deck cost for 100 sq ft deck: $2800-$6200 (including all the expenses with materials)
• Composite deck cost for 200 sq ft: $5200-$12000 (including all the expenses with materials)
• Composite deck cost for 500 sq ft: $11000-$25000 (including all the expenses with materials)

What is the Water Impact of Composite Decking?

When composite decking is exposed to water for a short period, it blocks moisture effectively because the plastic matrix stops capillary movement and the capped surface sheds water before it reaches the core.

The moisture stays on the top layer, the structure stays firm, and composite decking avoids rapid swelling or softening. Fungi also fail to colonize the surface because composite decking does not offer digestible cellulose.

When composite decking is exposed to longer periods of water, it starts trapping moisture at cut edges, ventilation gaps, and shaded underside zones. Uncapped boards absorb small amounts that trigger light mold films, while capped surfaces struggle when debris holds water.

Composite decking then develops mildew, slippery films, stains, trapped moisture pockets, fastener corrosion, swelling in low-grade composites, and faded pigments. Proper drainage and cleaning keep composite decking stable.

How Does Sunlight Affect a Composite Deck?

When composite decking is exposed to sunlight for a short period, it absorbs UV radiation and heat directly on the outer surface. UV rays start breaking down unprotected pigments, and exposed wood flour in uncapped composites begins losing cohesion.

Capped composite decking slows this reaction because the co-extruded shell contains UV stabilizers that shield the core. Sunlight also heats composite decking to 40-60 C° depending on color and density, and this rise in temperature increases thermal movement along each board.

When composite decking is exposed to prolonged sunlight, composite decking shows noticeable performance changes that accelerate during summer. These long-term problems include color fading, surface chalking, thermal expansion, contraction gaps, heat retention, sheen loss, material softening, and increased surface slickness.

Darker boards develop these issues faster because composite decking absorbs more UV radiation and heat. Proper spacing, UV-stabilized caps, and lighter color selections help composite decking maintain long-term stability and comfort.

How Frequently Should You Maintain Composite Decking?

You should maintain composite decking every 6-12 months. But it depends on the exposure to the dirt, climate, and debris accumulation. When you maintain a composite decking, you should follow the bellow steps.

• Clean deck surface: You should clean the composite decking by sweeping or hosing off leaves, dirt, and dust. This helps to prevent mold and staining on the deck surface.
• Wash with mild detergent: You should wash the composite decking with soapy water or a composite deck cleaner. This helps to remove grease, mildew, and surface dirt.
• Check fasteners and joints: You should inspect screws, clips, and board seams regularly. This helps to ensure the decking remains secure and prevents loosening over time.
• Inspect for stains or damage: You should spot-clean any spills or marks immediately. This helps to avoid permanent discoloration and keeps the deck looking new.
• Maintain drainage: You should ensure gaps between boards and under-deck drainage are clear. This helps to prevent water accumulation and prolong the deck’s lifespan.

How to Install a Composite Decking?

To install a composite decking you should follow the bellow 7 quick steps guide recommended by the Aqviz experts.

• Plan the composite decking project: First, you should measure the deck area, mark joist locations, and plan the board layout to ensure proper spacing and alignment.
• Prepare the surface: Second, you should clear the surface, install or inspect the joists, and ensure they are level and structurally sound.
• Install ledger board: Third, you should attach the ledger board securely to the structure, making sure it is level and properly flashed to prevent water infiltration.
• Lay starter boards: Fourth, you should place the first row of composite boards along the deck edge, leaving recommended expansion gaps of 6-10 mm (1/4-3/8 in).
• Fasten boards: Fifth, you should secure boards using hidden fasteners or screws per manufacturer instructions, ensuring uniform spacing and alignment.
• Cut and fit remaining boards: Sixth, you should measure, cut, and install the remaining boards, adjusting gaps around corners, posts, and edges.
• Finish edges and railing: Finally, you should install fascia boards, trim edges, and attach railings or stairs as needed to complete the deck installation.

What are the 6 Downsides of Composite Decking?

Composite decking is not a perfect deckin materials due to the following 6 downsides. So you should know these before starting a composite decking project.

1. Higher initial cost: Composite decking increases upfront expenses compared to natural wood, reducing immediate budget flexibility.
2. Heat retention: Composite decking can absorb and retain heat, which may increase surface temperature and reduce comfort on hot days.
3. Color fading: Over time, composite decking can reduce color vibrancy due to UV exposure, harming the deck’s aesthetic appeal.
4. Scratches and surface marks: Composite boards can accumulate scratches and scuffs, which decrease surface appearance and smoothness.
5. Moisture trapping in gaps: Poor installation or blocked drainage can reduce water runoff and harm underlying structures.
6. Weight and handling: Composite boards are heavier than wood, which can increase labor effort and reduce ease of installation.

How to Protect a Composite Deck?

To protect composite decking, homeowners need to maintain the capped surface, manage moisture movement, and control UV exposure so the polymer-wood blend stays stable during seasonal weather cycles.

Composite decking responds well to routine washing because cleaning removes organic debris that traps moisture and encourages algae growth. Composite decking also benefits from polymer-safe detergents and biodegradable mold removers that lift dirt without damaging the outer shell.

These cleaning routines help composite decking stay dry, reduce surface buildup, and avoid early discoloration in humid zones.

How Long Does Composite Decking Last?

A composite decking can last 30-50 years when the capped surface, internal polymer blend, and installation details work together to control moisture and UV exposure.

The durability of composite decking increases with proper board spacing, strong ventilation beneath the framing, annual washing, and UV-stabilized caps that limit fading during 30-60°C sunlight cycles.

The durability of composite decking can be reduced due to trapped moisture under low-airflow zones, debris that holds water against the surface, thermal expansion without proper gaps, fastener corrosion, and low-grade cores that absorb small amounts of water at cut edges.

What are the Options for Composite Decking?

These are the most used 5 composite deck options.

1. PVC decking: PVC decking is one of the best alternatives to composite decking due to its zero wood content, strong water resistance, and excellent UV stability that prevents fading in high-sun zones.
2. HDPE decking: HDPE decking is a reliable alternative to composite decking due to its strong resistance to swelling, predictable thermal expansion, and steady slip performance in wet areas.
3. Aluminum decking: Aluminum decking is a superior alternative to composite decking due to its complete moisture immunity, corrosion resistance, and high structural strength under heavy loads.
4. Fiberglass decking: Fiberglass decking is a durable alternative to composite decking due to its reinforced resin matrix that blocks UV rays, resists moisture intrusion, and stays stable in coastal environments.
5. Modified wood: Modified wood is a stable alternative to composite decking due to its reduced moisture uptake and improved dimensional control that supports long-term outdoor durability.

Read More About: Wood Decking: Know these Before Installing

Should you waterproof a composite deck?

No, you should not waterproof composite decking because composite decking already contains polymers and a capped surface that blocks water penetration and prevents the core from swelling.

Composite decking resists moisture naturally, handles rainfall without deep saturation, and maintains surface stability even in high humidity. The protective shell and UV stabilizers already deliver the moisture control that traditional waterproofing products try to achieve.

But you should protect the structure under composite decking because the framing absorbs water even when the composite decking stays dry. Homeowners should use flashing tape on joists, improve ventilation, and keep gaps clean to stop trapped moisture.

These practices protect the substructure, increase long-term durability, and prevent mold growth more effectively than applying waterproofing coatings on composite decking.