Painting exterior wood is not the best answer. I would use Cabots simi transparent deck stain. The reason being is that exterior wood needs to breath to have maximum moisture transfer...or dry quickly. When you paint it it may take longer to soak up water but it also takes longer to release water. That causes wood to rot. With Cabot's deck stain, it will breath. If it were my deck, I would buy some deck stripper, sodium hydroxide based, and follow the directions and pressure wash it off. The stripper will be alkyline causing the wood to turn a dark color. Then, apply a wood brightener/conditioner, Oxolic acid, to bring the PH back near 7. When the wood has dried, no more than 16% moisture content, roll on the Cabots but not too thick. No runs or puddles. While you roll it on, have someone back brush it with a good, wide paint brush. This will stop the puddles and runs while working the stain into the wood. Let dry for 48 hours and viola, a new deck/porch that will last 3 to 5 years. This is the correct way to do it even if it sounds like a lot of hassel. This is what I do for a living as well as restore and refinish log homes. This is the most effective way to maintain exterior wood. Replacing wood decking or painting it every year is a bigger hassel. If you don't want any hassels with it, rip it out and pour concrete.
