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Old 08-11-2007, 11:27 PM   #1
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'Belinda' is painted with Awlgrip. The paint job has lasted 10 years, but to be fair it has been crappy for the past three. The harsh tropical sun of sub equatorial Darwin has made the paint chalky. The dark blue colour has of course added to the deterioration.

I was chatting to an old salt yesterday and told him I was going to repaint in a lighter colour using International 2 part epoxy. He told me two things which I feel deserve the benefit of discussion here.

1) Undercoat with black. He says that is the standard in the aircraft industry because it is more impervious to damage from UV. Consequently he says the substrate will remain undamaged for longer.

2) Use a high quality, exterior house paint.

Interestingly, my house was painted 12 years ago with Dulux Weathershield, exterior gloss. A quick blurt from the high pressure water blaster makes it look like new, yet it exists in the same environment and under the same sun as the boat.

Has anyone any experience with non-marine coatings on boats?

Cheers.

David.
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Old 08-12-2007, 12:14 AM   #2
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I guess it really depends on how nice you want your boat to look. I certainly wouldn't use anything beside linear polyurethane.

Linear polyurethane (LP) paint is a wondrous thing — especially for older boats that suffer from chalky gelcoats or dingy aluminum finishes. When you paint with LP, you’re actually applying a thin layer of high-strength plastic over fiberglass, wood or metal surfaces, creating a waterproof, chip-resistant finish that can be expected to last 10 years or more. My previous LP paint job lasted 12 years and could have gone a few more. Chip resistance and ductility is somethng that you really want to have in a boat paint and I don't think you'll get it with a house paint.

I've seen a lot of Boeing aircraft being painted and never once did I observe a black primer coat being applied. I would hope that the UV didn't get that far.

Aircraft_primer.jpg
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Old 08-12-2007, 12:44 AM   #3
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Maybe the guide coating process is what he was refering to:

After drying, the gray primer was lightly misted with a black primer (spray can). This is called the "guide coat". The black primer was then sanded off with 400 wet sandpaper. This process identifies the imperfections in the prime coat and guides the sanding process until the surface is really smooth.
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Old 08-12-2007, 12:55 AM   #4
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Seems plausible. I had not considered using anything except urethane. But the bloke I was yakking to sounded knowledgable. What are the arguments for using single pack over two-pack and vice versa? For instance, International have developed 'Brightside' (single pack urethane), which has Teflon suspended within the paint. It is supposed to give flawless results off the brush; which could be a good thing for detail on deck where spraying is not possible without major work on my boat.

David
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Old 08-12-2007, 12:57 AM   #5
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Do you mean single-part versus two-part paint?
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Old 08-12-2007, 01:00 AM   #6
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Yup...Dialectic difference..In Oz we call it single pak...2 pack.

Cheers.

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Old 08-12-2007, 02:04 AM   #7
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In simple terms ...and trust me, acrylics, urethanes, polyurethanes, epoxies, acrylic aliphatic polyurethanes, linear polyurethanes can be a very complex chemistry discussion...but again in simple terms, a single part urethane cures in reaction with air/moisture and OH from moisture in the air or sometimes with UV or IR or a combination of all three. These paints will remain ductile as they have little or no cross-linking…they are typically less UV resistant as well.

If you look at acrylic urethane under a microscope you see the resin structure looks like a simple ladder. A polyurethane will look like an over reinforced truss structure due to cross linking. A linear polyurethane will primarily cross-link in a single plain thus maintaining ductility, yet still having the tight surface draw during curing to achieve that glass slipper look, chip and UV resistance. There are many other additives for UV resistance as well. This is in contrast to an epoxy which is very strong but brittle because the cross linking is in all directions.

Activation of Polyurethane requires the addition of isocyanate located in that second container of a 2-part system.

I actually called one of my polymer chemists to confirm this information.

Also, just for confusion purposes, urethane is not a component of polyurethane.
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Old 08-12-2007, 08:48 AM   #8
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So, what is your recommendation?

David.
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Old 08-12-2007, 11:59 AM   #9
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Quote:
Originally Posted by Auzzee View Post
So, what is your recommendation?

David.
Awlgrip.

Richard
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Old 08-12-2007, 05:54 PM   #10
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This is the hardest part....I've always used Sterling, however we shot our cockpit with Awlgrip and I must say that the Awlgrip laid down and pulled tight much better than the Sterling. I've had a lot of professionals tell me that Awlgrip is better than Sterling as well.
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Old 08-12-2007, 11:29 PM   #11
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Also, spaying dark colors like blue in LP are much much more difficult than white. If you read my blog, you'll see that it took the yard numerous attempts with midnight blue to get it right.

I'm seriously considering having my boat painted white in Ensenada on my way South.
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Old 08-13-2007, 12:48 AM   #12
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Thank you sincerely for your input. I will repaint the topsides in Awlgrip and I am leaning toward a light oyster grey at the moment. I am still looking at Subic bay for the ork...probably May/June '08.

Thanks again

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Old 08-15-2007, 09:08 AM   #13
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Hi Auzzee. I've used Brightside on Bedouin applied by brush and also seen Awlgrip applied the same way. Both give similar results in finish and application. I've got a mate who used house paint on his 52' yacht. It was easy to do; that was good as it lasted no time at all. Maybe a year at best. Then he had the job of totally removing the house paint and redid it with Awlgrip --- bitching non stop at the price of Awlgrip against houe paint, which was the only reason he used the housepaint to begin with.

Bedouin was a Royal Blue but I redid her in Brightside Squal Blue which is much lighter in shade. A much cooler yacht below and I'm thinking that it may stay longer looking better as the paint won't be soaking up as much heat.

Regards

Peter
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Old 08-15-2007, 09:48 AM   #14
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Hi Peter,

Was there any specific reason why you went with the single pack Brightside, instead of the 2 pak Awlgrip or International equivalent?

Best wishes

David.
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