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You can use a paintbrush or a dense broom. Leave the stripper on the deck for about an hour. Be sure to check and follow the manufacturer's instructions on how to use the chemical stripper.    This will completely remove all the remaining acrylic paint. The sealer will protect your deck from future stains.

Summary:
Apply a paint stripper on the old acrylic paint. Rinse the paint off using a high-pressure hose. Use a putty knife or a paint scraper to scrape the remaining acrylic paint. Let the deck dry fully. Sand the area using a random-orbit sander and 80-grit paper. Apply a sealer to your deck's surface, if needed.