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post #3 of Old 02-09-2013
Maine Sail
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Re: Bottom paint flag coat theory vs. reality

Originally Posted by 4arch View Post
I've read in several books, magazines, and forum posts that when applying ablative bottom paint it's wise to apply an undercoat of a contrasting color to act as a "flag" to indicate when the topcoat is worn through. I'm curious as to what kind of experiences people have had with this method in the real world?
Works tremendously well and allows you to not put on too much paint and avoids build up.

Originally Posted by 4arch View Post
Looking around boatyards at boats awaiting spring painting, I haven't seen boats with half worn-through top coats revealing contrasting color paint.
I see it all the time. My own boat with a black bottom has a few spots every year of red exposed. I usually rough up those areas with Scotch-Brite or my pressure washer and re-launch.

Originally Posted by 4arch View Post
In my own experience, the ablative paint loses all effectiveness and must be recoated well before it wears off.
That has not been my experience at all. A simple scuff in the spring gets it going again though I've done nothing and had it work perfectly. Are you buying "multi-season co-polymer ablatives?

Originally Posted by 4arch View Post
In the interest of minimizing paint buildup, it seems that it might be better to skip the flag coat and and to just apply single thin coat of ablative directly over the barrier coat.
I went with a HOT COATED red layer, 1/4" roller, then another thin coat of black with a 3/16" roller. It's been six years and we have zero paint build up.. Hot coating is CRITICAL for the first layer to adhere and bond to the barrier coat. It usually requires one guy rolling the last coat of barrier and the next guy rolling the first coat of bottom paint a few minutes behind him or "thumbprint" dry. In warm weather thumb print dry happens fast....

The ONLY glitch we had was that I allowed the Pettit rep to talk me into Hydrocoat. HUGE, HUGE mistake. It failed to perform, failed to "ablade" and it all had to come off. I went back to Ultima SR-60 and am back to great paint performance.......

Originally Posted by 4arch View Post
I'd appreciate people's thoughts and experiences on this. I just had my boat's bottom soda blasted and plan to barrier coat in the spring. Since I'm starting over completely I want to do things right and keep from getting to the point of having the extreme buildup I had before.
The last boat I did before this one was in 1997 and as of three years ago the bottom still looked perfect. It was hot coated and used a tracer color. The current owner kept up with the 3/16" roller only applying when the paint got thin.

I would highly recommend Interprotect 2000E.. It is a tremendous product that allows for LONG open times between chemical bonds barrier to barrier.... Also comes in white and gray so you can alternate to make sure you have good film thickness.

Please also be sure your hull is DRY. The biggest mistake people make is coating a substrate with too much moisture in it... Usually best to strip it in the fall and let it sit all winter to dry before barrier coating.

The biggest mistake people often make with ablatives is painting them every year as if they were hard paints. This defeats the purpose of using an ablative. If your coats are thin enough then you may need to paint each year.. This spring I only have a couple of areas to touch up, leading edge of keel, bow, rudder and around the prop.... I used a 1/4" roller last year after removing the Hydrocoat (what a PITA). I can get two+ seasons out of one coat with a 1/4" roller.

-Maine Sail / CS-36T

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Last edited by Maine Sail; 02-09-2013 at 10:25 AM.
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