A. Paul Fisette responds: I understand your client’s reluctance to use treated boards in a beautiful custom project. But the problem is caused by using untreated wood in an exposed location.
Your choices for installing and finishing the deck boards were sound ones. But the end grain of the wood is absorptive, like a sponge. Water is splashing off the stairs onto the ends of the boards, soaking in, and encouraging rot. Unfortunately, no paint job can stop that.
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