Polyurethanes

[LazyJack]

Why are they not favored for marine brightwork?
How do the UV resistant gloss exterior polyurethanes hold up outdoors?
Are these finshes difficult to maintain?
Jus curious...

[paul oman]

I was rather surprised to learn about two years ago that nearly all 'clear cote' type products have very little to no UV blockers added to them. I was also shocked to learn the price of UV blockers for clear coats (I guess that are special so as not to affect the clarity of the coating).

I'm no expert in this niche, but I know of only 2 clear coats with UV blockers and one of them is auto clear coat.

paul oman
progressive epoxy polymers

[Memphis Mike]

It all depends.

My boat stays on a trailer when not in use under a carport. It is used in fresh water only so far.

I used Minwax Spar Polyurethane on the bright work four years ago. It's held up really well and is just now showing signs of a few needed touch ups.

[Skiff Junkie]

Last year I started using Detco's Crystal varnish on my boat. This has the UV protection mixed in. So far, on the parts I used it on, it's held up pretty well.

[Dan McCosh]

I don't quite understand the question. Polyurethanes are the most common types of varnish for marine use these days.

[Paulyboy]

Originally posted by paul oman:
I was rather surprised to learn about two years ago that nearly all 'clear cote' type products have very little to no UV blockers added to them. I was also shocked to learn the price of UV blockers for clear coats (I guess that are special so as not to affect the clarity of the coating).

I'm no expert in this niche, but I know of only 2 clear coats with UV blockers and one of them is auto clear coat.

paul oman
progressive epoxy polymersAuto clear coats seem to last a long time come rain, shine, winter, summer, smog, fog, etc. Would this be an intermediate or low maintenance alternative?

[Wild Wassa]

Originally posted by LazyJack:
"Why are they not favored for marine brightwork?"

Some say they are too neutral for timber and just don't like the look. People are used to the warmth of a varnish ... and some may have had trouble with cheaper less stable paints failing under UV.

"How do the UV resistant gloss exterior polyurethanes hold up outdoors?"

Perfectly fine if you spend the bucks and buy high quality paint. One can spent only $100 for 5lts of a marine poly/oil blend varnish (like Cabots) or $250 for the equivalent in a marine clear poly (Boatcraft Pacific's Aquacote).

"Are these finshes difficult to maintain?"

On the cans (I've tried Cabots, Norglass and BCP's, all marine polies) they all say, "after 2-3 years, sand lightly and recoat." Which to me means, applying only one or maybe two new coats of clear. I only put on 3 coats of clear poly or only 3 coats of a poly/oil blend varnish, when I'm painting bright.

Real varnish (if you can still buy it or if you make your own) requires at least 6-7 coats and is a life sentance handed down yearly.

If you do use a clear over epoxy, consider using your manufacturer's non-yellowing hardner in the epoxy rather than just using their normal epoxy hardener.

Warren.

[ 03-16-2005, 03:16 PM: Message edited by: Wild Wassa ]

[LazyJack]

Thanks for the replies. I've had good luck with Captains Z-spar...I know how to use it and it seems to hold up fine. I didn't know if perhaps there was something else out there just as good if not better, it's been a long time since I tried anything different.

[paul oman]

To continue on this subject:

I suspect auto clear coats (2 part acrylic polys, I believe) are probably very high sovlent products and probably pricey. But there certainly are alternatives.

While I sell clear coat products, I usually tell people that traditional varnish is my favorite (any brand). In my tests over epoxy with all sorts of clear coats, the vanish kept the shine the longest and the best. Maybe because it is thicker and thus a thicker film coat. Also the varnishes add that warmth of color the 'fake' clear coats don't and it seems to have natural UV protection.

When I lived in Tx and sailed Galveston Bay, I would seal my wood trim with epoxy and then topcoat with 2 or 3 coats of vanish. It would stay good for two seasons, much longer than either one alone. If I were doing it all over, I would sovlent thin the first coat (s) of both the epoxy and the varnish for still better bond.

paul oman
progressive epoxy polymers

[LazyJack]

Thanks Paul
That sounds like pretty solid advise especially as I imagine Galvastin bay is not a particularly benign environment for any coating. I too have used varnish over epoxy with good results but only over unobstructed surfaces were sanding the epoxy flat after application is easir (traditional lapstrake boat would be brutal)I've also never have tried to 're-wood' such a finish because I've never needed to...hmmm...but I'd hate to have to try to...trade-offs I guess

[JimD]

I used Endura brand two part I purchased from an auto/aircraft/boat painting company with mixed results over epoxy. In a few places it started to flake off and in other areas held up much better. I can't explain why. I was very careful (so I thought) to clean and prep the epoxy first. Clear two part poly over epoxy has become quite a common way to protect epoxy from uv but as others say it seems unwise to assume they all block uv equally. A couple years ago WB mag ran an article of a high end wooden runnabout manufacturer spraying it over epoxy for their very pricy boats.

[ 03-16-2005, 01:54 PM: Message edited by: JimD ]