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As others have stated, polyester is inferior for use with/over wood. For use in the sheathing process, polyester can be marginally acceptable. However, since it does not bond well to wood, it is completely unacceptable for fillets and taping seams on a S&G (if your sheathing starts to come up, the failure is not likely to be catastrophic if detected and repaired early - if your hull seam fails on a S&G, you'd better be close to land, because your boat could be in two pieces in a heartbeat).
Just so I can avoid being entirely discouraging... you can still build a cheap S&G by taping the seams with epoxy inside and out, and not sheathing in fiberglass. Not as strong or as abrasion resistant, so you'd have to take more care in paddling, beaching, etc., but better than polyester.
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Guillemot Kayak - High Performance Wooden Sea Kayak Designs