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Old 24-06-2021, 08:45   #1
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Overwhelmed by antifouling choices

Hello all. Iím repainting the bottom of my Aloha 32. She had years of thick bottom paint that was flaking off so I started scraping and sanding with a orbital and 80 grit. I got to a point where the bottom still is 80% covered in bottom paint and 20% exposed gelcoat but Iím afraid Iím going to damage the gelcoat. Or that I may have damaged the gelcoat already.

My plan is to sand off ad much bottom paint as I can without damaging the gelcoat anymore, prime the bottom and lead keel with Interprotect 2000e, them paint 2 coats of antifouling. The boat will be living in fresh water for about a year before moving to the intracoastal. Iím in central Florida.

First question: Is this a good plan?
Second question: Can I use Interlux Bottomkote Copper bronze for my antifouling? The price is low and I have a small budget.
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Old 24-06-2021, 09:20   #2
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Re: Overwhelmed by antifouling choices

It’s hard to say without seeing the condition of the current bottom paint. Usually, if the bottom paint is in good enough condition (see how subjective that is?), you can just go over it with new bottom paint after sanding it (to facilitate a mechanical bond). Catch is, you have to know what was on there first (hard, ablative?) to ensure compatibility.

Priming over existing bottom paint doesn’t seem right to me, but that’s not a bridge I’ve ever had to cross so I’ll let someone else answer that part for you.

In instances where I was unsure about the condition or compatibility of the existing coat, I have always removed it entirely and started fresh. That has always given me a good baseline going forward and removes all doubt.


Best of luck with whatever you end up doing.
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Old 24-06-2021, 09:26   #3
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Re: Overwhelmed by antifouling choices

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Priming over existing bottom paint doesnít seem right to me, but thatís not a bridge Iíve ever had to cross so Iíll let someone else answer that part for you.
Iím a little worried about priming over the existing paint. I think itís a soft ablative because it seems to rub off on your hand.

I would like to take it all down with the sander but I feel like Iím already damaging the gelcoat in spots and I have a lot more bottom paint to take off.
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Old 24-06-2021, 10:01   #4
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Re: Overwhelmed by antifouling choices

Not sure I would be so worried about the gelcoat as it is a permeable coating anyways and the Interlux 2000 is epoxy and would seal any expose f/g anyways. Did you have blisters?
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Old 24-06-2021, 10:03   #5
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Re: Overwhelmed by antifouling choices

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Not sure I would be so worried about the gelcoat as it is a permeable coating anyways and the Interlux 2000 is epoxy and would seal any expose f/g anyways. Did you have blisters?
No, luckily no blisters. You are giving me more confidence to move forward. Thank you.
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Old 24-06-2021, 10:30   #6
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Re: Overwhelmed by antifouling choices

Hey Hawk!

Here's an excellent thread from last year that may be of some help. A few of us specifically discussed how much sanding/grinding/ scraping... and there are pictures!

Be the Change - Bottom Paint
https://www.cruisersforum.com/forums...nt-236837.html

Good luck!
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Old 24-06-2021, 12:51   #7
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Re: Overwhelmed by antifouling choices

Thank you for the link!
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Old 24-06-2021, 12:56   #8
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Re: Overwhelmed by antifouling choices

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Originally Posted by Hawkmouth View Post
First question: Is this a good plan?

Interlux doesn't recommend applying 2000e over one-part paints, as I understand it, so you would want to remove the existing paint.


Quote:
Second question: Can I use Interlux Bottomkote Copper bronze for my antifouling? The price is low and I have a small budget.
It will work but there may be better choices. That's a hard paint that will tend to accumulate on the hull over the course of years. I prefer ablative paints. There are also paints that have more effective fouling chemistry than copper alone, and given that Florida is a heavy fouling area you might want to consider them. I use Micron Extra, for example.
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Old 24-06-2021, 12:57   #9
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Re: Overwhelmed by antifouling choices

Do not epoxy paint over bottom paint, unless this is a temporary boat.

A quality job is all about encapsulation and adhesion. Don’t worry about exposing gelcoat. As a matter of fact, a really good job will get all the paint off, gelcoat exposed, then sand the gelcoat for proper epoxy adhesion.

If you paint over bottom paint, there will likely ultimately be an adhesion failure—then the only thing keeping that epoxy barrier in place will be cohesion—epoxy molecules Bonded together.

I’d get allllll that old paint and barrier off and apply a nice layer of barrier with sufficient dry film thickness. Tie the first coat of bottom into the top coat of epoxy according to manufacturer specifications.

I recommend two coats of ablative. This is one of those jobs where cutting corners now will cost you more in the long run (unless, once again, you plan to sell the boat real soon)
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Old 24-06-2021, 16:48   #10
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Re: Overwhelmed by antifouling choices

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Do not epoxy paint over bottom paint, unless this is a temporary boat.

A quality job is all about encapsulation and adhesion. Donít worry about exposing gelcoat. As a matter of fact, a really good job will get all the paint off, gelcoat exposed, then sand the gelcoat for proper epoxy adhesion.

If you paint over bottom paint, there will likely ultimately be an adhesion failureóthen the only thing keeping that epoxy barrier in place will be cohesionóepoxy molecules Bonded together.

Iíd get allllll that old paint and barrier off and apply a nice layer of barrier with sufficient dry film thickness. Tie the first coat of bottom into the top coat of epoxy according to manufacturer specifications.

I recommend two coats of ablative. This is one of those jobs where cutting corners now will cost you more in the long run (unless, once again, you plan to sell the boat real soon)
So I should just continue sanding and scraping all the old bottom paint off. Then interprotect 2k, then an ablative antifouling? Thank you for your advice.
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Old 24-06-2021, 17:06   #11
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Re: Overwhelmed by antifouling choices

You can get chemical paint stripper that will get that ablative paint off. I dont know yr yard rules on using it though.
I agree with post #9 otherwise
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Old 24-06-2021, 18:10   #12
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Re: Overwhelmed by antifouling choices

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Originally Posted by Hawkmouth View Post
So I should just continue sanding and scraping all the old bottom paint off. Then interprotect 2k, then an ablative antifouling? Thank you for your advice.
That MAY not be necessary, although getting down to the bare underlayment and applying an epoxy barrier coat can prevent osmosis and would let you start with a foundation of bottom paint that you are familiar with (no compatibility worries). If you do go that far with it, it’s worthwhile to seek and destroy any and all blisters (if any) because the barrier coat is designed to seal everything out... or in if moisture is already in there.

You mention cost sensitivity, so I’ll say that bottom paint doesn’t NEED a primer (but do not apply it on a painted surface- I’m referring to hull paint). IF your current bottom paint isn’t flaking off (that would be a sign that it’s failing to adhere), you can sand it all with a coarse grit and just apply your new bottom paint- assuming the bare spots are gelcote. You can always revisit the more robust solution on your next haul out.

Long term concerns with that approach are bottom paint compatibility- which you may have addressed and osmosis. In my opinion, you don’t NEED to break the bank if you’re not able right now.

I’ll caveat that by recommending a call to the paint manufacturer for a quick q&a for any considerations unique to that paint.
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Old 25-06-2021, 05:22   #13
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Re: Overwhelmed by antifouling choices

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Originally Posted by Creedence View Post
That MAY not be necessary, although getting down to the bare underlayment and applying an epoxy barrier coat can prevent osmosis and would let you start with a foundation of bottom paint that you are familiar with (no compatibility worries).
My original plan was to just sand the existing bottom paint down a little and paint a new bottom over it but there was flaking paint so I started scraping that off and fairing the chips with the sander. Also, I donít know what the existing bottom paint is. I think my option at this point is to get all the existing bottom off.

Anybody have recommendations for an ablative antifouling I could use in Florida fresh and salt water?
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Old 25-06-2021, 05:54   #14
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Re: Overwhelmed by antifouling choices

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Anybody have recommendations for an ablative antifouling I could use in Florida fresh and salt water?
When you're unsure it's a good idea to check what local yards are using. Just ask. Usually those products are a good balance between price and efficiency.

If something isn't used at all, there's often a good reason for it.
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Old 25-06-2021, 07:11   #15
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Re: Overwhelmed by antifouling choices

Hey there Hawk, your Aloha 32 is a great boat and deserves a proper solution. Nearly bought one myself. Something I have learned from doing a similar job on my newly acquired Ontario 32: sand it all back to gelcoat, then make sure that you put on ENOUGH Interprotect 2000.

I am currently in the late stages of sanding off a bottom that was coated in both VC-17 and Interprotect 2000. Then I will be reapplying the same products. It is a truly miserable job which has extended over months, so why am I doing it? When the current coating of Interprotect 2000 was applied, the people paid to do it only half-assed the job. First, the bottom was sand- or soda-blasted to remove old ablative bottom paint. This left the bottom gelcoat with a number of pocks and divots. These were not filled, nor were the last traces of bottom paint removed by sanding. Instead, what looks to be a single gallon of Interprotect was applied, instead of the recommended minimum 4 gallons.

The net result of this was that when my boat is out on the hard and the weather gets warm enough, a series of small bubbles would form across the bottom of the boat. When the weather cooled down enough, the bubbles would almost entirely disappear. Sanding and investigation revealed that there was no actual osmosis present. I discussed this phenomenon with tech representatives from Interlux and they said that it was the result of having too thin a layer of Interprotect, probably coupled with areas of insufficient bonding due to the remaining traces of old bottom paint. The water is able to penetrate the thin layer and then gets trapped behind the epoxy. When it heats up, the vapor pressure forms the bubbles. This was happening to a fresh-water boat that is only in the water for six months at a time. If you are going blue-water down south, your baby will be possibly be immersed for years at a time.

In order for Interprotect to provide an actual barrier to water penetration it must achieve the thickness levels recommended by Interlux in their literature. Otherwise you are just wasting your time. I mention this because you say that you are on a tight budget and Interprotect is an expensive product. An Aloha 32 will require 4 or 5 gallons in order to get adequate thickness. In addition to my current boat, I have known other boats and owners who have decided that since they had gotten nearly two coats out of a single gallon, that was "good enough." No need to spend all that extra money. Which leaves a subsequent owner, like me, with a real problem and a miserable job to do. If you think sanding off old bottom paint is bad, you should try sanding off epoxy! Pay close attention to ALL of Interlux's instructions, they are there for a reason. I know this because I have done very successful, and long-lasting, Interprotect bottom jobs on two previous boats. After 15 years of exposure, those bottoms were still flawless.
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