polyurethane or epoxy

A good impregnable paint over the polyester will help, but it must be maintained in good condition with frequent inspections for breaches of the barrier.

 

Watson and I are probably tainted a bit. I still remember the building craze of the 60's and 70's, where plywood boats popped up every other backyard, adorned with lovingly applied polyester sheathings and wire brush paint jobs. This goes without mention, of the too many to count soles, stringers and transoms I've replaced over the years, also bedded, bonded and tabbed with this mythical goo. And as you'd expect, prep and techniques where the usual culprits, when the inevitable delamination occurred, but this is what you would also expect from a novice dinghy builder, isn't it. This is the main reason I suggest epoxy. It's easier to get good and durable results from a novice, with epoxy.

 

I'm convinced.

 

I totally agree that even a really crappy job with epoxy will likely be sucessful but an educated novice is more than capable of achieving a long lasting job with poly, ive done repairs on production boats built by some of the largest builders in the country where they have done everything wrong leading to said repairs and ive also seen boatowners do a great job of repairing their boats by educating themselves. Basically if you are capable of doing good work you can produce a long lasting job with poly, even on plywood, but if you are a hack you probably should use epoxy. Btw,i grew up in New Zealand where epoxy has been in common usage in boat building since the 50s but it was never marketed as the one size fits all goo, so when i was an apprentice we used what was appropriate for the task at hand but i cant say i ever saw a plywood boat sheathed using polyester resin, i never saw that until i moved to the US.

Steve.

Steve.

 

There was an ugly time here in the states, Steve. A building craze took over after WW II, because plywood, formerly known as laminated wood, which wasn't trustworthy, got real waterproof glues and became reliable. The new wonder goo's became available and boat building took off. At first (late 40's and early 50's) they were plank over frame, but soon they got sheathed with polyester. New, light and better preforming designs appeared and of course polyester production, took hold and the wonder goo was the cure all to every wooden boat.

This caused thousands of old wooden boats to die, but worse were the back yard attempts during the 60's and 70's where plywood and strip planked builds got the same treatment.

Epoxy though commercially employed after WW II, wasn't publicly accepted until the 70's and not widely used until the early 80's. This was mostly because the boat builders had previously seen a wonder goo and were tainted with the appearance of yet another. The Gougeon brothers helped a great deal, at dispelling the myths associated with epoxy, but it took time to sink in. I remember this time well and every marina had a few stylish catamarans or monos, laying against a back fence, with the tattered remains of a blue poly tarp danging off it, much like its polyester sheathing was.

We're in complete agreement that an educated novice can get good results with polyester, though my experience has been, they have an easier time with epoxy, right out of the box. So, if you're a guy that reads the instructions first, after buying an Ikea kitchen set, you'll probably do just fine, but if you're the type that doesn't read the instructions, until you realize you have several, seemingly extra parts, well . . .