When Not to Sand Composite Decking: Safer Prep Methods

Composite decking is popular for its low maintenance and durability—but sanding it like wood can cause irreversible damage. Understanding when not to sand composite decking will save you from melting, discoloring, or voiding the warranty. This guide covers what happens when you sand, safer prep alternatives, and when light scuffing is acceptable.

Why Sanding Composite Decking Can Be Risky

Composite decking combines wood fibers with thermoplastic resins. When sanded, friction heat can soften or melt the plastic, exposing the fibers and leaving permanent scuff marks. Once the surface seal is broken, the boards can fade unevenly or absorb stains differently. Manufacturers often warn that sanding voids finish warranties.

Recommended Tools for Surface Prep

• Soft-bristle cleaning brush or deck scrubber
• Low-pressure washer (under 1500 psi)
• Mild biodegradable cleaner or deck soap
• Plastic putty knife for scraping sticky debris
• Fine hand pad (non-abrasive) for light scuff repair

Ideal Grit Sequence for Edge Repairs (If Sanding Is Unavoidable)

• 220 grit: Lightly feather small scratches or raised fibers.
• 400 grit: Blend transition areas without cutting into the core material.
• 800 grit: Final smooth-out to restore uniform sheen.

Step-by-Step: Cleaning and Prepping Composite Decking

1. Rinse off debris. Use a garden hose or low-pressure washer to remove dirt and pollen.
2. Apply cleaner. Spray a composite-safe cleaner and allow it to soak for 10–15 minutes.
3. Scrub gently. Use a soft-bristle brush following the board grain. Avoid steel brushes—they can scratch the surface.
4. Rinse thoroughly. Flush away residue and let the deck dry fully.
5. Inspect for localized damage. For small scuffs, you may feather-sand edges using 220 Grit (25-pack) sheets wrapped around a foam block. Keep motion slow and even.
6. Polish with finer grits. If the area dulls, step up to 400 Grit (50-pack) for blending and finish with 800 Grit (100-pack) for a uniform surface sheen.
7. Clean again. Wipe the repaired spots with water and allow to dry before applying any sealant or UV restorer.

Special Cases: Stains, Scuffs, and Sun Fading

For grease or oil stains, use mild dish soap or a composite deck cleaner rather than abrasives. For deep gouges, replace affected boards instead of sanding—they will never match the texture perfectly. If boards are faded, consider a composite restorer coating instead of mechanical sanding.

Pro Tips

• Work on cool, shaded days—heat increases melt risk.
• Always sand along the grain if spot-sanding is unavoidable.
• Use wet/dry sandpaper to control friction and prevent heat buildup.
• After sanding, clean residue immediately to avoid permanent marks.
• Keep extra matching boards for future repairs instead of sanding worn planks.

Aftercare

• Rinse deck twice a year to prevent mildew buildup.
• Reapply UV protectant every 2–3 years.
• Inspect for raised screws or warped edges before cleaning season.

FAQs

• Can I use an orbital sander on composite decking? No. Even on low speed, it can overheat and burn the surface.
• What if my composite deck has mold? Use a mold remover specifically formulated for composites—never bleach.
• Can I paint over composite decking after sanding? Generally not recommended; most coatings won’t adhere well.
• How can I restore color without sanding? Apply a water-based composite deck restorer or color reviver instead.

Watch & Learn

Summary: Composite decking should rarely be sanded—heat and abrasion can cause permanent surface damage. Stick to cleaning, chemical restoration, or very fine spot sanding only when absolutely necessary. Using proper fine and super-fine grit sheets ensures safe, controlled touch-ups that preserve your deck’s look for years.