Some good tips for painting a wooden porch are to make sure that the wood is dry and clean, replace any loose nails with nails of the next size up, fill holes and damaged areas with an exterior-grade putty, apply fresh caulk to all of the joints, and prime bare areas and putty-filled locations with an oil-based primer. When finishing the porch, use a high-quality oil-based finish and paint any hand rails with a high-quality acrylic paint.
When painting a wooden porch it is ideal to paint each surface of each piece of wood to achieve a proper level of protection against the elements. If painting the connecting sides of each plank is not possible. then caulk all of the connecting joints to create a seal before painting. When it isn't possible to paint the underside, an oil finish or stain provides better protection compared to paint. Partially painted wood exposed to the elements absorbs moisture rising from underneath and is prone to splitting, chipping, cracking, bubbling and rot.
Wood porches that have previously been sealed with an oil or oil stain require the use of paint remover and sanding to fully remove the treatment before painting. Likewise, if a porch has previously been painted, you need to strip the paint from the surface completely before applying a fresh coat of paint or oil treatment.