How clean to reapply ablative bottom paint? - SailNet Community
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post #1 of 30 Old 03-24-2020 Thread Starter
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How clean to reapply ablative bottom paint?

Hey all, question same as the title.

Background:
I bought some west marine bottom paint, the ablative type. I only put on about 1.5-2 layers on and that lasted only 15 months in the SF bay. It has about 80% coverage left, but lots of gelcoat showing through. Also a decent amount of growth.

Last time I got growth off by spraying an acid, waited for the crackling to stop, and then wiping away the mush. My concern is that if I do that, all the existing paint will come off since it is indeed very ablative, which maybe isn't a bad thing other than I'll require more new paint. To me it will ultimately mean that I take most/all of the paint back down to the gelcoat.

Should I still do that method, or should I just use a stiff brush and get the hull 'mostly' clean and paint over it? I can trailer the boat but would love to get a full 2 years out of this very ablative paint.
Thanks!
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post #2 of 30 Old 03-24-2020
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Re: How clean to reapply ablative bottom paint?

You don't have to take the remaining paint off, just rough it up with 80 grit. Ablative paint wears off over time so buildup is not usually a problem. Just make sure your paint is compatible with what you used last time.
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post #3 of 30 Old 03-24-2020
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Re: How clean to reapply ablative bottom paint?

Mostly clean will mostly peal off. As Rich said, good paint can stay, but all of the slime has to go. ALL of it.

You know the right answer. And no, most of us never use acid. Any of the paint remaining after acid washing, by the way, will no longer contain copper and won't be helping you. Never use acid on bottom paint you want to keep.

Brush, scraper, sand paper, and hard work. If you damamge the gelcoat it will need sealing. If you had pulled the boat while the paint was still somewhat effective this would have been much easier.

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post #4 of 30 Old 03-24-2020
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Re: How clean to reapply ablative bottom paint?

Most of us pressure wash the hull when it is still wet at haul out. Then sand and paint.
Once the growth has dried it is much harder to remove. Perhaps you can rent a pressure washer (or have one) and it should do most of the work. Otherwise, maybe there's someone in your area that does soda washing.
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post #5 of 30 Old 03-24-2020
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Re: How clean to reapply ablative bottom paint?

Quote:
Originally Posted by RichF28 View Post
You don't have to take the remaining paint off, just rough it up with 80 grit. Ablative paint wears off over time so buildup is not usually a problem. Just make sure your paint is compatible with what you used last time.
Important to use compatible paints...the manufacturer will list which are
Otherwise your labor is in vain.

There is no easy way....shortcut to do this correctly


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post #6 of 30 Old 03-24-2020
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Re: How clean to reapply ablative bottom paint?

Don’t forget that whatever paint sloughs off your hull when you clean or scrape it needs to be picked up before it gets to the water. Our marina pressure-washes in a paved area that drains into a sump that gets filtered to remove the toxic materials. We have to vacuum any antifouling sanding dust - preferably before it hits the ground.
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post #7 of 30 Old 03-25-2020
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Re: How clean to reapply ablative bottom paint?

I don't know about westmarine paint, but I used Petit Horizons for many years. I find it extremely forgiving. I literally pressure was the bottom when it comes out of the water and knock any loose growth off, and paint right over the rest. No sanding, no chemicals. Pressure wash, paint, done! The bottom of the keel and the spots where the stand pads were get paint RIGHT before splashing and the paint still adheres.

I usually get 2 seasons out of a paint job, and have even pushed it to 3!

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post #8 of 30 Old 03-25-2020
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Re: How clean to reapply ablative bottom paint?

I see some owners using scrapers on big growths. I just have it power-washed in the fall, sand and paint in the spring. Part of the reason for sanding, for me, is to reduce the build-up of multiple ablative coats.

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post #9 of 30 Old 03-25-2020
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Re: How clean to reapply ablative bottom paint?

I've never heard of applying an acid to remove stuff -- except perhaps as a stripper to remove ALL paint.

We pressure wash when the boat comes out in the Fall, removing most of the slime. If there's any larger, harder bits I'll go at it as soon as I can, before it gets too hard.

In the Spring I scuff the bottom, and then apply new paint as needed.

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post #10 of 30 Old 03-25-2020 Thread Starter
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Re: How clean to reapply ablative bottom paint?

Muriatic acid is great to remove marine growth, but yeah basically that would mean a full strip of all the paint. I'm going to try to strip it with brushes/powerwashing first but not sure if that will be possible. I'll show you what i'm dealing with...
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