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Old 29-04-2010, 17:07   #1
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Fairing Under or Over Barrier Coat

I have recently had the hull soda blasted. The good news is that 500# of bottom paint is not in a landfill somewhere and will no longer be dragged along with the rest of the boat.

The bad news is that the blasting punched through the gel coat and requires a bit of fairing. Apparently there was so much paint on the hull (25 yrs worth) that the blaster couldn't maintain a light touch. Not a single blister though so that's good news.

With the gelcoat breeched by the blaster dime sized dimples a barrier coat is in order. I hadn't intended this if there were no blisters but now I need to provide a barrier and will bite the bullet and use an epoxy barrier coat.

But I can apply it to the cleaned hull and fair our the dimples etc after or before the barrier coat or both, or between coats as I'll do at least 2.

Questions:

fair after, before or between barrier coats?

What sort of fairing would be recommended under barrier coat and over barrier coat?

My instinct is to fair under and not attack the barrier with sanding as ... perhaps it could be sanded through.

I might be able to use a cheaper fairing since it's sealed inside the epoxy barrier coat. Outside it would have to be underwater spec.

How smooth does the barrier coat go on and what sort of roller is best?

Do I need extra coats on leading edges? It's not a wear surface as it will have ablative paint over top so that seems not required.

Tips please on barrier coating. This weekend I will be ready to fair or barrier.
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Old 30-04-2010, 12:50   #2
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Aloha,

I am not an expert but I've faired before barrier and it seems to work well. I've used just plain epoxy as a barrier with no filler included and used a roller designed not to fall apart in epoxy to apply it. Try not to have drips in the epoxy barrier coat as they will be hard to sand out once its dried and while sanding you may remove the barrier coating. Three coats is what I used but, like I said, I'm no expert. Seemed to work well.

I'm glad you found no blisters. That's great news.

regards,
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Old 30-04-2010, 13:49   #3
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fairing

Def, I think I would fair under, probably with west. Grind where necessary, clean, apply unthickened coat, and while wet fill with west thickened with 407. Let that go off, sand, rinse, and repeat till fair. Then seal that with 2 coats of unthickened west, sanding between coats. Now you have 1 uniform, sanded surface; proceed with interprotect to as many coats as you can stand... they say 4 or 5 is good; last time I did it I went 6, but it was a smaller, 25' center console. (Working lying on my back with the boat jacked up about 2' above the trailer).

Different colors let you see misses, but are not necessary if you do enough coats. Use the yellow foam rollers, or the 6" white ones with the rounded ends from Lowe's will also last for a while. Buy many rollers... like 24 (probably more), and just go around and around the boat. By the time you're all the way around you'll probably be tacked up well enough to do another. They say you can go up to 2 weeks between coats with out sanding, but the only thing I'd stop for would be weather (and/or darkness).

Good luck.

Best, Bob S/V Restless
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Old 30-04-2010, 15:27   #4
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How important is it to get every last bit of paint off? There are some hard to get spots at the keel to hull joint and it's all fairing and not hull. Same with keel, it has already been Wested and has some "thin" spots with paint on it... not well sanded. I am thinking of just Westing it over and not doing the interprotect except on the hull and part way down the keel.

What's the deal on barrier coating keels and so forth?
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Old 30-04-2010, 15:55   #5
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fairing and sealing

If the keel is lead it doesn't need sealing, except possibly because the bottom paint might stick better to sanded epoxy than to lead, and the epoxy might stick better to the lead than bottom paint would. But if salt water gets at the lead it's not going to hurt it.

If the keel is steel or cast iron then it's a whole different issue.

If the keel to hull joint area seems intact, and the existing fairing is secure, then I'd just seal what you've got.

Best, Bob S/V Restless
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