I build have been building picnic tables out of SPF for the table tops and bench seats. I use pressure treated for the supports and legs. My problem is the finish on the top and seats. After a year some of them start peeling/flaking in spots. Nothing major just in spots. I live in Michigan so the tables set outside all year mostly unprotected. In my process, I run the boards through the planer and do some light sanding first. Then stain them, let them dry, and apply 3 coats of “Minwax¯ Helmsman¯ Spar Urethane ” semi-gloss poly (oil based) on all sides. Am I fogetting a step? Should I use a sanding sealer first? My thinking is that the finish should last least two years. Your comments and suggestions are welcomed. (I do not poly the pressure treated, just stain those).
Thank you for taking the time to read my question.