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Author Topic: Epoxy Barrier Coat  (Read 4474 times)

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Ross Fisher

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Epoxy Barrier Coat
« on: February 02, 2007, 05:56:03 PM »

I have just hauled my boat to re-do the anti-fouling and anodes. I have had the bottom water blasted to remove the built up weed and coral that has accumulated since last anti-foul ( approx 16 months ago.)
The anti-foul has not lasted well and there are a number of patches on the hull where the paint has disappeared, and  a thick build up of marine life has occured on these spots.
My shipwright claims that the epoxy barrier coat has not been "keyed" and that the anti-foul is not bonding properly to the epoxy and falling off.
He is proposing that sanding the hull will not cure the issue, and that I should spend some $1500 to have the hull sand-blasted to form a keyed surface.
When I hauled the boat 4 months ago to have it surveyed, the anti-foul coverage was thinning but consistent. There were no bare spots at that time.
 Does this suggestion sound reasonable? Does a good sanding normally provide a key for the anti-foul? What experiences have other owners had with paint bonding to the barrier coat?
Your advise and experiences will be gratefully appreciated.
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Ross Fisher
# 1486  "Avventura"                            
2000 Catalina Mk11 Wing Keel
M35B
Melbourne, Australia

David Sanner

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Re: Epoxy Barrier Coat
« Reply #1 on: February 03, 2007, 01:58:44 AM »

It seems that there are nearly as many opinions on this as boat yards.

It sounds like you had something similar to my problem...
the bottom paint builds up year after year until it's so thick it
starts to flake/chip off.   That can also be aggravated by a weak
layer in there somewhere, either in the bottom paint itself or
a weak bond between the original epoxy barrier coat and
the first coat of bottom paint.

The options I heard last year were either to do a chemical
peel of all the bottom paint (a few thousand dollars) or
blast it... along with a few others variations.


I wound up chipping off as much paint as I could with
sharp/flat tools and having the yard spend several extra
hours sanding.  It wasn't purported to be the best/cleanest
solution but the idea was to save money and if I keep at
this for my next few hauls I should be able to thin the
paint out enough and hopefully cure 95% of the problem
areas.

It's been a year since my last haul and the bottom is
still looking good.

btw: After the chipping and sanding the yard did wind up
touching several areas with barrier paint.  (1/2 gal) Their idea
about barrier paint was that it was fundamental in creating a bond
between the gel coat and the bottom paint but really didn't
do that much to protect blisters.  Blisters... it seems there's
another long list of theories for what causes and how to protect
your hull from them.

If you wind up going all the way down to your gel coat others
have suggested that you use a barrier paint that is a different
color than your bottom paint so you'll know when to stop sanding
on subsequent hauls.

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David Sanner, #611 1988, "Queimada" San Francisco Bay

Jon Schneider

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Re: Epoxy Barrier Coat
« Reply #2 on: February 03, 2007, 06:55:41 AM »

Ross, are you sure that you've used a compatible paint?  I would certainly think that sanding and then applying a compatible, tenacious coat of anti-fouling would work.  I had noticed that my boat's bottom was chunking off in large flakes from season to season (northeast sailor), so I'm having it sand-blasted (actually not sand, but an industrial version of baking soda), so I can start again with a fresh, clean bottom, which I will first barrier coat.  BTW, having gone the way that Dave suggested on a 26 footer, I definitely opted for the blasting option.  Man, stripping, scraping, and sanding an entire hull is back-breaking work.  Never again for me.
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Jon Schneider
s/v Atlantic Rose #1058 (1990)
Greenport, NY USA

Ron Hill

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Re: Epoxy Barrier Coat
« Reply #3 on: February 03, 2007, 06:36:08 PM »

Guys : This is a repeat, but worth saying again.
I had my bottom "blasted" to remove ten years of hard bottom paint.  Jon is right - taking all of that paint off is tooo tough!!
I put back on 2 epoxy barrier coats.  The 2nd coat was put on before the 1st coat had cured (so I DIDN'T have to sand).  Then before the 2nd coat cured, I put on a single coat of hard bottom paint.  That way it chemically bonded to the final barrier coat.
Then days later I put on the final coat of bottom paint which is ablative.  All of those coats of barrier, hard paint and ablative paint are different colors.  That way when I see a certain color I know where I am.

Ross : To answer your question - yes, you'll have to sand the epoxy barrier coat with a medium grit paper to get the bottom paint to stick.
A few thoughts.    :wink:
« Last Edit: February 04, 2007, 04:53:38 PM by Ron Hill »
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Ron, Apache #788

David Sanner

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Re: Epoxy Barrier Coat
« Reply #4 on: February 07, 2007, 03:08:16 AM »

Ron, how much paint did the blasting take off?  1/2 , 3/4 of the thickness?

I assume from your post that it didn't take it all the way down to
the gel coat but just thin it out as well as give the next paint something
to grab on to.

My problem wasn't that the paint was getting too thick, it was already too
thick and eventually the paint just started failing in large chunks because
of bad layers long ago....

It was chipping off mostly at the initial layer.  Probably caused by
either the gel coat wasn't prepared properly originally or
the epoxy coat between the gel coat and the bottom paint had
some curing issues (too wet/dry).

If my chipping is down to a minimum on my next haul perhaps
getting the bottom blasted to thin out the paint overall might
be cheaper/better than trying to do the extra sanding yet again.

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David Sanner, #611 1988, "Queimada" San Francisco Bay

Ron Hill

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Re: Epoxy Barrier Coat
« Reply #5 on: February 07, 2007, 05:41:40 PM »

David : I took it all the way down to the gel coat.  The original barrier coat was too thin and I actually reapplied 4 barrier coats.  The 4 coats were sprayed on, that's why I only mentioned 2 coats because most people will roller it on - then 2 coats of epoxy barrier is enough.

I blasted off 11 coats of paint.  You are probably correct that there was some waxy "mold release" left on your hull and/or the barrier coat wasn't sanded so the paint didn't get something to stick to.
I found that with spraying on the barrier and then paint, that when you finished spraying on one complete coat you could start on the next coat!  That's why most people start early in the morning and get 2 coats of barrier on and then the bottom paint by dusk - not having to sand in between.    :thumb:
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Ron, Apache #788

Ross Fisher

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Re: Epoxy Barrier Coat
« Reply #6 on: February 08, 2007, 04:06:20 AM »

Guys,
Thanks for your response and sharing your experiences with me.
I bit the bullet and went ahead with a blast clean of the bottom of the boat and then a thorough sand.
The result is very impressive and resulted in a pristine surface which I will now paint with another light coat of epoxy, followed (whilst uncured,) with a quality anti-foul. Hopefully, this will provide a base that will last for many years with disciplined annual maintenance, and gives me the confidence to know what makes up the protective layer on the bottom of the boat.
If this sounds like self justification, it is! I spent more than I intended or wanted, but will convince myself it was money well spent!!
Cheers,

Ross
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Ross Fisher
# 1486  "Avventura"                            
2000 Catalina Mk11 Wing Keel
M35B
Melbourne, Australia

Steve Sayian

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Re: Epoxy Barrier Coat
« Reply #7 on: February 08, 2007, 08:18:46 AM »

I had the bottom soda blasted a few weeks ago and am going to apply 2 coats of barrier coat followed with 2 coats of hard paint
The question I have is which brands are compatible with the vinyl ester treatment the bottm had applied at the factory (or does it matter)?

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Steve Sayian
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Wing, Std Rig, Kiwi Prop
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Ron Hill

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Re: Epoxy Barrier Coat
« Reply #8 on: February 08, 2007, 02:02:30 PM »

Steve : You need to ask that question - to the maker of your barrier coat.  They will know the most compatable paint.

When I put on the 1st coat of paint so it would chemically bond to the barrier, I used only one coat of hard paint.  The I used ablative after that.  Again barrier, hard and ablative coats were all different colors.    :thumb:
 
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Ron, Apache #788

Steve Sayian

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Re: Epoxy Barrier Coat
« Reply #9 on: February 10, 2007, 04:23:11 PM »

Ron,

I spoke to the Catalina dealer today (Eastern Yacht Sales) and they said that any of the top names in barrrier coat are all compatable w/the vynal esther gel coat. 
Thanks for the tip!
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Steve Sayian
"Ocean Rose"
1999 Mk II
Wing, Std Rig, Kiwi Prop
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Ron Hill

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Re: Epoxy Barrier Coat
« Reply #10 on: February 10, 2007, 04:44:59 PM »

Steve : Did that Catalina dealer realize that the barrier epoxy was NOT completely cured when you're applying the bottom paint ??  There is a chemical reaction between the uncured barrier and the fresh paint so it "sticks" better.
Think I'd trust the opinion of the maker of the epoxy barrier, rather than a Catalina dealers opinion!
A thought.   :?:
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Ron, Apache #788

Steve Sayian

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Re: Epoxy Barrier Coat
« Reply #11 on: February 11, 2007, 01:59:07 PM »

Ron,

Yes the Cat dealer has done lots of barrier coats.  He mentioned about the 'thumb print' test to see tell when the first coat is ready for the second, third, etc and then application of the first coat of bottom paint. Also mentioned and discussed was the criticality of temperature, temperature, and temperature.
Looking forward to starting this when the tenmp is about 45 degrees warmer!
Thanks.
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Steve Sayian
"Ocean Rose"
1999 Mk II
Wing, Std Rig, Kiwi Prop
#1448, Hingham, Mass
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