Puzzled about polys

[Dusty Yevsky]

I'm not sure if this has ever come up before but can anyone enlighten me about the similiarlities and differences between marine one part polyurethanes and "regular" clear furniture finishing polyurethanes? I realize this is a very unfocused question so let me expound a bit. I've used clear polyurethanes many times in the past for furniture finishing and while it might not be the most refined finish it has some desirable qualities. Very durable and one of the easiest, most forgiving to apply. So when I started to mess with boats I figured polyurethane paint would be similiarly well behaved. Much to my dismay it is anything but. Regardless of my approach rolling, brushing or spraying only produces so-so results with lots of touchups and buffing involved. Why is this so different from clear? Are these two products in the same class or are they related by name only? I intend improve my technique with marine poly but am perplexed about the nomenclature.

Dusty

[merlinron]

i believe the main difference is that the pigmented stuff has more accellerator in it. the clear being deliberately slowed down to get a good gloss so that it reflects the substrate well. without all the accellerator it is more forgiving of back brushing(tipping) and small goof-ups, making it much more user friendly. if your painting outside with poly colors, stay out of the sun!

[Wild Wassa]

"Are these two products in the same class or are they related by name only?"

The same brand of polyurethane taken from the same tin, on any two days running ... is related in name only for the average user.

Most marine polyurethanes give poor results to non professional users: they are clumpy by nature. They need straining, with fine micron filters. They have 'no' self-levelling properties. They are almost impossible to apply and to achieve a high degree of consistent and repeatable finish unless using a spray application. They are only meant for spray applications although the manufacturers encourage otherwise, which I feel is the real problem for part-time painters. They are very slow to go off, this I find ridiculous in this modern age. They stay soft for longer than the manufacturer’s state, which negates a speedy blocking out and rapid working. They do not forgive the painter who does not find the perfect thinning proportion and they look far too plastic when badly applied.

Except for, the Dupont Imron range, International Perfection both the undercoat and topcoat, even a rank amateur like blind Freddy looks like a pro when using Perfection thanks to the self levelling characteristics and the water based 2 pack marine polyurethanes ... like BoatCraft Pacific's Aquacote.

Aquacote is available in the US. I use Aquacote, I find it to be a very fine product and well worth the expense.

I use Aquacote and Aquacote Clear as my standard range of marine finish, because of the rapid setting of the paint. With Aquacote I can be blocking out the paint in only 15 minutes from the time of application ... when the temperature is above 26C or at two hours at 20C. Which means that it is possible to apply up to 12 sanded coats in a 24hr period. Compared to most other marine polyurethanes that only allow one blocked out coat in 24hrs, Aquacote is extraordinary. At 20C I can brush Aquacote Clear at 5 minute intervals, at 26C I can brush on coats at 2 minute intervals.

Automotive 2 packs give excellent results on boats, if the boat can cope and if the type of purpose warrants it.

The fine finishing here is almost exclusively done in 2 pack polyurethane on both wood and on the composites.

Warren.

[AstoriaDave]

Dusty, "polyurethane" covers a wide range of formulations. What brand and type are you using?

[Dusty Yevsky]

I'm using Interlux one part for boats and have used a few different clear polys for furniture. Seems odd that Interlux, which is pitched at the home builder, wouldn't make their product a little more user friendly. This is the only marine poly I've used but I've heard from other builders that generally all marine polys have the same handling characteristics. I've tried all the advice from Interlux and still end up with mixed results. I suppose I'm wondering why clear polys are easy to apply and self level whereas marine is a PITA to apply and doesn't level at all. According to Interlux's data sheet they say 24 hours between coats. What's the point of having a fast non-leveling paint then? I think I will try Warren's suggestion and try Aquacote.

Dusty

[AstoriaDave]

Dusty, something is wrong. Could be you need to add reducer.

[Lew Barrett]

I'd echo Dave's sentiment. Technique? Temperature? Chemistry? Interlux paints can and should be thinned to working consistency using their system brushing fluids.

[Todd D]

Interlux Brightsides (their one part ployurethane) can be a bit fussy, but once you get the hang of it you will get very nice results.

The picture below is a model that I brush painted with Interlux brightsides. I think it took 4 coats to get this finish. I wet sanded with 400 grit before the last coat and then buffed out the dust motes with Finesse-It II after the final coat.

The trick to getting it to level is proper thinning. I generally take some neat paint, add a bit of thinner, paint a test spot on a piece of glass, and then add more thinner as needed until I get the right consistancy.

TD

http://www.todddunnmicroyachts.com/2007/aidan-22.jpg

[Dusty Yevsky]

Yes, I am bound and determined to figure out marine polys. I'm just a little perplexed that I can take clear polys straight out of the can and get a great finish with not much effort whereas the marine polys are decidely more difficult. The something extra in the marine poly that allows it to hold up in a marine environment must also makes it harder to apply. I'm curious to know what that something is.