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Old 09-22-2017, 06:37 AM   #1
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Bottom Paint application

Newb question on bottom paint. What is it that makes additional coats of AF not worth it or ineffective? Meaning if two coats are good why wouldn't 4 or 5 be better? What goes south when you coat too much? Adhesion? Obviously the wallet goes south a bit....
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Old 09-22-2017, 07:42 AM   #2
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Your question is probably paint type specific.

My paint recommends at least 2 coats, but does not go on to say more is better.

My guess is more is better only if you are going to move the boat enough to keep wearing off outer layers and you are not going to repaint every year or two.

The common practice is to use a different color underneath, and when it shows, time to repaint.

For non ablative type paints, you might need to contact tech support to find out if after a certain thickness, the leaching of the copper or biocide becomes ineffective.

Be careful of individual claims of effectiveness, sometimes the environmental factors give better results more so than the paint or application.
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Old 09-22-2017, 07:56 AM   #3
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Basically it depends a bit on the anti-fouling type as Ablative or hard type and or epoxy based or similar,

The normal Ablative type if it gets to thick (to many coats) it can suffer from adhesion issues and chipping issues, this is why it is recommended every 5-6 years it is wise to remove all your old anti-fouling right back and re prime and start the process again,

Applying a third coat for some manufacturers is actually recommended and nearly all recommend additional coats in high wear area's

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Old 09-22-2017, 09:53 AM   #4
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I don't do the "two colors" thing, I wait for my diver to start complaining that the paint isn't working like it should be.

Using two different colors means you will have two partially filled cans of paint to deal with when you're done. That's a waste of paint and money.

As above, additional coats can be applied in high wear areas to lengthen the life of the paint job.

The major bottom paint manufacturers have extensive websites that will answer most of your questions and help you determine the best paint for your particular boat and location.
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Old 09-22-2017, 01:17 PM   #5
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I never waste paint or money.....just finished painting my bottom an hour ago..zero waste.....plus its an ablative paint tip....most paints dont follow this suggestion.

Its just the first coat after a bottom strip thats diffetent and pretty easy to calculate within a quart or two.

Anyway I makes it easy to see when the aftercoats have worn thin (again ablative types) and often recommendrd by pros and it is easy and doesnt cost much if you can figure how much you need.

Even West Marine discusses it....

"Ablative paints in particular must be thickly applied. Apply extra coats in areas of turbulence such as the bow, rudder and leading edge of the keel. With copolymer and ablative paints, if you use a different color for the base coat, you’ll know it’s time to recoat when it begins to show through. Use the paint manufacturer’s coverage chart for an educated guess as to how much paint you’ll need to do the job. Get some special transducer antifouling paint to touch up any underwater transducers"
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Old 09-23-2017, 02:53 AM   #6
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Thanks guys. I did a crappy job of asking the question...yes, ablative paint. I like the idea of the two colors...seems to make sense. The waste of some remaining in the can sort of goes back to my question. Couldn't I apply that in the heavier wear areas to put it to good use and then go about the second color doing the same with the extra left over from that color. So maybe I end up with two good coats all over and then up to four on the waterline etc. where there is more turbulence. I'm in a marina with little current and at this point only weekending the boat. May go two weeks without moving it. Won't get into the "Which paint?" discussion. Talking to my neighbors about what works best for them and will go from there.
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Old 09-23-2017, 03:47 AM   #7
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... The waste of some remaining in the can sort of goes back to my question. Couldn't I apply that in the heavier wear areas to put it to good use and then go about the second color doing the same with the extra left over from that color. So maybe I end up with two good coats all over and then up to four on the waterline etc. where there is more turbulence...
It`s not wasted, keep it for next time.
Or, 2 coats all over, plus a 3rd in the high wear areas, waterline, bow, etc, makes sense. Limit build up by a good pre-painting wet sand. Not dry, I`ve done that, I had to, but don`t.
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Old 09-23-2017, 06:48 AM   #8
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I would use up the whole amount of paint of each color. If you are doubling up on the first off color coat in high wear areas, it will last longer once down that far.

My 40 has a 34 foot waterline and a little over 13 foot beam. I use exaxtly 1.5 gallons of Interlux Fiberglass Bottomkote NT per coat. But every paint has a little different coverage, so does the nap on the rollers.
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Old 09-23-2017, 08:30 AM   #9
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I use exaxtly 1.5 gallons of Interlux Fiberglass Bottomkote NT per coat. But every paint has a little different coverage, so does the nap on the rollers.
Yes and also due to the "shoe and hat" factor.
How much ends up on those surfaces LOL
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Old 09-23-2017, 08:59 AM   #10
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It`s not wasted, keep it for next time.
.......
Yea, the PO of my boat gave me what he had left over in the can. I would have had to use a trowel to apply it. The shelf life of an opened can of bottom paint is not very long even if you reseal the lid.
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Old 09-23-2017, 08:32 PM   #11
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First color or second, I think I will just keep applying until it is gone. The last thing I need is another can of ANYTHING on my boat, in the deck box, or in my garage. I think if I actually put everything I already have (6 months in) for the boat on the boat it would sink.
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Old 09-23-2017, 08:44 PM   #12
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First color or second, I think I will just keep applying until it is gone. The last thing I need is another can of ANYTHING on my boat, in the deck box, or in my garage. I think if I actually put everything I already have (6 months in) for the boat on the boat it would sink.
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Old 09-23-2017, 11:32 PM   #13
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Last year blue, this year black. Next year blue again. Pretty simple, really.
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Old 09-23-2017, 11:33 PM   #14
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First color or second, I think I will just keep applying until it is gone. The last thing I need is another can of ANYTHING on my boat, in the deck box, or in my garage. I think if I actually put everything I already have (6 months in) for the boat on the boat it would sink.
Yep, that was definitely worth repeating.
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Old 09-24-2017, 03:59 AM   #15
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Yea, the PO of my boat gave me what he had left over in the can. I would have had to use a trowel to apply it. The shelf life of an opened can of bottom paint is not very long even if you reseal the lid.
Looks like you got conned with old paint in unsealed cans. My leftover antifoul keeps well between applications, seal it well with the clamp on the can, it`s fine.
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Old 09-24-2017, 07:40 AM   #16
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I also put a piece of plastic wrap down on the surface of the paint to keep it from skinning over itself...but not so much anymore.....as....

I have figured out that living aboard with really no good place to store paint, I am better off just bying what I need for the job and what I might do in the next 6 months or so.

Even if more expensive that way.
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Old 09-24-2017, 02:30 PM   #17
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Looks like you got conned with old paint in unsealed cans. My leftover antifoul keeps well between applications, seal it well with the clamp on the can, it`s fine.
Not "conned" at all. The PO had the paint left over from the last paint job and he gave it to me. It cost me nothing and in retrospect, was worth nothing.

For my situation, hard paint is recommended and I get three to five years on one application (two coats).
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Old 09-25-2017, 09:49 AM   #18
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"So maybe I end up with two good coats all over and then up to four on the waterline etc. where there is more turbulence."

Growth is usually greater at the WL because light can reach things that use light to grow.
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Old 09-25-2017, 10:37 PM   #19
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Please forgive the newbie for slightly off topic, but how long does the antifouling last on a trawler in the PNW? I know that is a vague question as paint type and location will have effect. I'm trying to move into a trawler style vessel, so lots of research.
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Old 09-25-2017, 11:38 PM   #20
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Please forgive the newbie for slightly off topic, but how long does the antifouling last on a trawler in the PNW? I know that is a vague question as paint type and location will have effect. I'm trying to move into a trawler style vessel, so lots of research.
Depends.
I spent years in Coal Harbour, used to the conditions there, used to my paint lasting well on the hull and on the running gear. Then I moved to Saltspring, so now, keeping the boat in Long Harbour for the warm 1/2 of the year, my running gear gets covered in barnacles in no time. Last year I didn't paint, but had to dive twice last summer to get rid of barnacles. My hull was still OK after 2 full years. I won't wait that long again, as I should haul annually to do my zincs and the RG needs attention at least that frequently.
Do you keep your boat near Black Creek? Or elsewhere on the south coast? Conditions are likely unique to your home location, so conditions as far south as the PNW are likely not relevant to your home marina.
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