you may have to sand it down and refinish it like a real wood deck. as long as surface is roughed up it will take a paint easier. if you have and splits from using nails that will let water under your paint and cause peeling too. you may need something more than regular porch paint in that case. I suggest a product called Restore from Home Depot. Its normally used to extended the life of a standard wood deck or dock. It fills in cracks and splits in the wood and leaves an antislip finish. It can be mixed in an array of colors to match what you need.