Remove any existing nails using a hammer and pry bar. Then, scrape off any loose paint using a carbide scraper or sander.
Cut the bottom of each spindle to correspond to the angle of the bottom railing using a compound miter saw or sliding compound miter saw. Lay out the spacing on the new bottom rail. Apply an oil based primer to the spindles and bottom rail. Allow at least 30 minutes to dry.
Nail or screw the spindles in from the bottom of the rail (Image 1), then repeat on the top rail with the same spacing. Reuse the top hand rail and connect the balustrade to the columns using 2 1/2 inch galvanized finish nails, or stainless steel screws. Use the two-part polyester wood filler as needed to patch any holes (Image 2). Using an orbital sander, sand the wood filler after it has dried. Complete by priming the wood and caulking the nail holes. Finish with a final coat of paint.