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Old 10-11-2015, 09:40 PM   #1
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Bottom Paint and Barrier Coat

I have noticed in the two year of owning that the bottom paint flakes off (down to the barrier coat) in places.

Any experience in how to get adhesion and stick?

I thought last summer it was just my hull. But after looking at 4 other boats hauled out the same day as mine it is a common occurrence. There seems to be many flakes and loose spots that appear. Does the barrier coat have to be Etched?, Sanded?, or Primed? Or is this an indication that the barrier coat was not applied correctly?
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Old 10-11-2015, 11:09 PM   #2
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I have noticed in the two year of owning that the bottom paint flakes off (down to the barrier coat) in places.

Any experience in how to get adhesion and stick?

I thought last summer it was just my hull. But after looking at 4 other boats hauled out the same day as mine it is a common occurrence. There seems to be many flakes and loose spots that appear. Does the barrier coat have to be Etched?, Sanded?, or Primed? Or is this an indication that the barrier coat was not applied correctly?
Is yours hard or ablative?
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Old 10-11-2015, 11:33 PM   #3
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I have put on two coats of ablative last summer when I bought her, and two more this spring. I do not know what type is in the middle of the coats though. But what ever is there flakes all the way off to the barrier coat.
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Old 10-11-2015, 11:35 PM   #4
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Sounds like the bottom paint was applied too late. Most barrier coats require the bottom paint to be applied within an hour or so after application of the last coat of barrier coat. The best course of action at this point is to sand off the old coats of bottom paint and apply a couple of new coats of barrier coat followed by two or three coats of epoxy bottom paint.
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Old 10-12-2015, 06:06 AM   #5
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Sounds like the bottom paint was applied too late. Most barrier coats require the bottom paint to be applied within an hour or so after application of the last coat of barrier coat. The best course of action at this point is to sand off the old coats of bottom paint and apply a couple of new coats of barrier coat followed by two or three coats of epoxy bottom paint.
Yes, I had this same problem. Did the barrier coat in the Fall and ran out of time. Boat was left in a heated storage building over the winter. Applied ablative in the Spring and it was flaking off when the boat was hauled again the following Fall. Repainted and it happened again. Contacted Interlux and they made exactly this recommendation. Was able to literally blow off a lot of the bottom paint with a pressure washer...sanded the rest. Interlux told me to scuff the barrier coat for a good mechanical grip for the one additional layer of epoxy barrier. Apply the first coat of bottom paint while the epoxy barrier layer was "thumb print" tacky to get a chemical bond. This required that the job be done in four sections (45 foot boat) in order to get the bottom paint on before the epoxy barrier kicked over completely. I used a hard red bottom paint for the first layer followed as quickly as possible by the next layer of black ablative (within the recoat window). This procedure had also been recommended by the guys at the Interlux tech line. All of this was done in one long day with my spouse mixing and me applying. Second coat of ablative was applied the next day...again still within the reapplication window. No issues and that was six years ago. Starting to see evidence of red around aft chines....touch it up every couple of years. The rest of the bottom paint is still holding up fine. That said, I pressure wash the bottom myself at the Fall haul outs as I don't trust the summer help at the marina to not wreck the ablative. Nice kids, but they're used to hard bottom paint for the most part.
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Old 10-12-2015, 06:52 AM   #6
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How old is your barrier coat and how thick is the bottom paint accumulation? My Downeaster is 40 years old and after 25 years (when I bought it) of accumulated hard bottom paint, sections would crack and some flaking occurred. Ended up sand blasting the hull down to the gell coat and starting over with new barrier coat the year we faired and repainted the hull. No more cracking and flaking issues.

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Old 10-12-2015, 11:24 AM   #7
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Yes, I had this same problem. Did the barrier coat in the Fall and ran out of time. Boat was left in a heated storage building over the winter. Applied ablative in the Spring and it was flaking off when the boat was hauled again the following Fall. Repainted and it happened again. Contacted Interlux and they made exactly this recommendation. Was able to literally blow off a lot of the bottom paint with a pressure washer...sanded the rest. Interlux told me to scuff the barrier coat for a good mechanical grip for the one additional layer of epoxy barrier. Apply the first coat of bottom paint while the epoxy barrier layer was "thumb print" tacky to get a chemical bond. This required that the job be done in four sections (45 foot boat) in order to get the bottom paint on before the epoxy barrier kicked over completely. I used a hard red bottom paint for the first layer followed as quickly as possible by the next layer of black ablative (within the recoat window). This procedure had also been recommended by the guys at the Interlux tech line. All of this was done in one long day with my spouse mixing and me applying. Second coat of ablative was applied the next day...again still within the reapplication window. No issues and that was six years ago. Starting to see evidence of red around aft chines....touch it up every couple of years. The rest of the bottom paint is still holding up fine. That said, I pressure wash the bottom myself at the Fall haul outs as I don't trust the summer help at the marina to not wreck the ablative. Nice kids, but they're used to hard bottom paint for the most part.
Absolutely agree
I used Interlux Barrier and followed the instructions which req 1st coat of bottom paint within the "window" which depends on temp & humidity.
It took 2 good Wx days to get 3 Barrier & 1st bottom paint coat on - then applied addn'l bottom paint w/ timing not an issue
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Old 10-12-2015, 01:19 PM   #8
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I'd estimate 90% of all boat paint issues are due to application.
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Old 10-12-2015, 07:32 PM   #9
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Interesting. One guy told me that the last barrier coat was not applied correctly. If I understand it now, the last barrier coat has to (within specs) be top coated with a hard epoxy bottom paint as a base coat for the ablative.

Thanks. Makes me think of more spring pre launch work.

Thanks for the info...
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Old 10-12-2015, 07:33 PM   #10
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I'd estimate 90% of all boat paint issues are due to application.
I'd say more like 100%!!
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Old 10-12-2015, 08:04 PM   #11
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I'd say more like 100%!!
Well, there have been occasions of manufacturers having problems with their paints, but you're right that most paints are well tested and applied properly do a good job.
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Old 10-12-2015, 08:10 PM   #12
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I'd estimate 90% of all boat paint issues are due to application.
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Old 10-12-2015, 08:42 PM   #13
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Interesting. One guy told me that the last barrier coat was not applied correctly. If I understand it now, the last barrier coat has to (within specs) be top coated with a hard epoxy bottom paint as a base coat for the ablative.

Thanks. Makes me think of more spring pre launch work.

Thanks for the info...
Interlux didn't specifically advise to start with a hard bottom paint over the last coat of barrier epoxy. I could have applied ablative as the first paint coat as long as it went on while that last barrier coat was still tacky. The objective is to get that chemical bond.

I used Interlux CRC hard bottom paint (don't believe it's actually a two part epoxy) for that first paint layer because I thought I might want to switch from the Micron Extra ablative to hard paint at a later date. In that case, the hard bottom paint would be easier to sand to achieve a good mechanical tooth/grip than the rock hard epoxy (the ablative would all be sanded off as it's not a good base for hard paint...in my opinion). When I asked Interlux about compatibility between their hard bottom paint and their ablative, they said no problem...just get the ablative on within the recoat window...once again to achieve that chemical bond between the hard and ablative layers. Their web site at the time had excellent charts and tables regarding compatible products and cure/over coat times.
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Old 10-12-2015, 08:48 PM   #14
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Any thoughts on using Coal Tar Epoxy for ? We are soon to start sand-blasting a 48 foot Steel hull bottom and hoping to do the thing "Once" and be done with it for a long time. We got this recommendation from a Commercial Ship's Captain.
Any pro's or con's on the above material would be appreciated.


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Old 10-12-2015, 08:58 PM   #15
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I have used the coal tar epoxies to seal oil soaked concrete prior to putting down regular epoxy. I would not use it on a boat as lots of things don't like to stick to it.
I think you are better off using one brand from start to finish. I used americote 235 then used their bottom paint. I too only want to do this occasionally so we put 6 coats of epoxy on Florence prior to bottom paint. The last time Florence was done to bare steel was about 25 years ago and that was with three coats of Devoe epoxy so I think we should get about the same this time. I hope to be around to supervise the next one.
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Old 10-12-2015, 09:05 PM   #16
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Any thoughts on using Coal Tar Epoxy for ? We are soon to start sand-blasting a 48 foot Steel hull bottom and hoping to do the thing "Once" and be done with it for a long time. We got this recommendation from a Commercial Ship's Captain.
Any pro's or con's on the above material would be appreciated.


Thank You
I'd give Interlux or any of the other company tech lines a call.
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Old 10-13-2015, 06:32 AM   #17
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Any thoughts on using Coal Tar Epoxy for ? We are soon to start sand-blasting a 48 foot Steel hull bottom and hoping to do the thing "Once" and be done with it for a long time. We got this recommendation from a Commercial Ship's Captain.
Any pro's or con's on the above material would be appreciated.


Thank You
I don't think coal tar epoxy is legal/available anymore is it? Even if it is, it wouldn't make a good bottom coating for a boat. It was used on pilings and barges as a tough coating.
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Old 10-13-2015, 01:14 PM   #18
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Interlux didn't specifically advise to start with a hard bottom paint over the last coat of barrier epoxy. I could have applied ablative as the first paint coat as long as it went on while that last barrier coat was still tacky. The objective is to get that chemical bond.

I used Interlux CRC hard bottom paint (don't believe it's actually a two part epoxy) for that first paint layer because I thought I might want to switch from the Micron Extra ablative to hard paint at a later date. In that case, the hard bottom paint would be easier to sand to achieve a good mechanical tooth/grip than the rock hard epoxy (the ablative would all be sanded off as it's not a good base for hard paint...in my opinion). When I asked Interlux about compatibility between their hard bottom paint and their ablative, they said no problem...just get the ablative on within the recoat window...once again to achieve that chemical bond between the hard and ablative layers. Their web site at the time had excellent charts and tables regarding compatible products and cure/over coat times.
Absolutely agree
I've done CRC ablative over Interlux barrier twice (different boats) w/ good results
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Old 10-14-2015, 07:51 PM   #19
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Coal Tar epoxy, it's still used on steel hulled pontoon house boats. Had not thought of it a a yacht coating before. These boats mostly stay in one place in fresh water. The steel tubes begin to leak near the water line as the tar flakes off over time. It's thought of as a ten year coating by the house boat guys. I have no personal experience with it. They usually start by sandblasting the hull pressurizing the tanks for leaks welding them up if possible, and coating. Appearance is not important to these guy's.
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Old 10-16-2015, 02:56 PM   #20
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I had the same issue of ablative paint flaking of several years ago. Spoke to Interlux, issue was there were too many layers of paint. In my case, there is a coat of red and then blue top coat(s). Instructed not to paint until almost all the blue is gone. Seems to be working so far....
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