Remove dirt and dust from all the surfaces by washing them with a household can you sale sand wpc deckingdetergent solution or a commercial cleaner made for this purpose. Again, rinse thoroughly.
If you intend to paint your composite deck, first prime it with a quality boat composite sheetsexterior latex stain-blocking primer recommended for use on plastic materials. You should not prime if you intend to apply a deck stain.
Complete the job by applying a top quality latex floor and deck paint in a satin or semi-gloss finish (higher gloss levels have better mildew resistance and are easier to clean). If you didn’t prime Deck Boards and Railing Lumber the surfaces, you can apply a quality acrylic latex solid color deck stain recommended for use on composite decking.