Mix 1/4 cup liquid dish detergent with one gallon warm water. Dip the scrub brush in the solution and scrub away any dirt or debris from the surface of the wall. Make sure to clean the entire surface, including the very top and bottom of the wall. Allow the wall to dry for 24 hours.
Mix the polyacrylic with a paint stick for 90 seconds. Scrape the sides and bottom of the container as you stir. Pour the well-stirred polyacrylic into a paint tray.
Apply a layer of polyacrylic onto the surface of the fence with a paint pad applicator. Allow the polyacrylic layer to dry for two hours or the amount of between-coat time listed on the label.
Sand the surface of the wall with a belt sander. Sand just enough to roughen the surface of the polycrylic.
Repeat Steps 3 and 4. Apply at least five thin coats to achieve adequate outdoor protection.