Hey, I've met a carpenter who's going to make me a new viv and possibly more if I like his work. I'd make them myself but the vivs would look ugly as hell

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So what sealant is best for him to use all over and for joins etc? Hopefully it's going to be made of some nice looking wood and keep in mind it's going to be for my BRB so high humidy is a factor.
Thanks in advance hot any help.