Blistering - SailNet Community
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post #1 of 17 Old 06-23-2014 Thread Starter
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Blistering

Hey guys, my 1979 Ontario 28 has developed some quarter sized blisters on her port underbelly. I have found that most of my leaks and standing water problems on the boat have been on this side, is that where the problem lies? Or is in the cheaping out with resins in the late 70's on these boats? I have fixed most of the scupper and through hul problems, now to the hull, how do you decide when to fix the blistering ? How do you fix it ? take the gelcoats off, interprotect then bottom paint ?

Any help is appreciated.

NB there are only 20-30 blisters at present....

Mike
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post #2 of 17 Old 06-23-2014
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Re: Blistering

The first thing to check is the nature of the blisters, by grinding one or two down. Sometimes you get blisters in the paint, caused by poor adhesion at one of the layers - these are not true blisters, and nothing to worry about. Usually caused by the yard applying paint in less-than-ideal conditions (too damp, not enough/too much time between coats, etc).

For 20-30 true blisters, I woudn't be taking all the gel coat off. Grind them down, epoxy, then interprotect the whole bottom, then bottom paint. Will probably have to repeat this every few years.

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post #3 of 17 Old 06-23-2014
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Re: Blistering

I stopped counting at 300 blisters on a previous 1981 Catalina 25. I wouldn't remove the gel coat. I used a carbon steel counter sink drill bit to open all the blisters.

West System has excellent and inexpensive literature on this very topic. Followed their instructions and used their products and achieved professional results. Make sure you have "peanut butter" consistency with the filler. I applied "mayonnaise" consistency and the filler sagged .

Applied 5 coats of Interlux System 2000 water barrier + VC17.

If I had to do it again I would do the exact same thing (except for the sagging filler!)

Good luck and post some pix!
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Re: Blistering

Use their colloidal silica additive. I use it wherever I want epoxy to stay put while it's setting.
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post #5 of 17 Old 06-23-2014
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Re: Blistering

[QUOTE=oomfh;1952634]I stopped counting at 300 blisters on a previous 1981 Catalina 25. [QUOTE]

Once you find yourself in a situation like that you'd be better off to sand or soda blast the hull to open the blisters up, rinse with fresh water & let her sit to dry out.

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post #6 of 17 Old 06-23-2014
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Re: Blistering

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Originally Posted by MarkSF View Post
Use their colloidal silica additive. I use it wherever I want epoxy to stay put while it's setting.
BUT! it's like grinding IRON .. a softer mix for the final fairing is suggested. I like to use silica for the filling.. and fairing filler (tan color) on top of the silica

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post #7 of 17 Old 07-04-2014
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Re: Blistering

I just ground out the blisters. Mostly in the gelcoat and outer layer of mat. I think I want to pre-seal each ground blister site with epoxy before applying the epoxy filler to better seal the glass. Has anyone done this? What are your thoughts about the need to do this? Has anyone compared the West and Mas systems to see which is better, i.e. ease of use, pot life, sagging potential, ease of sanding, etc?
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post #8 of 17 Old 07-04-2014
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Re: Blistering

Try Interlux Watertite for filling the blisters, it's a lot easier to fair than silica and can be used below the waterline
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post #9 of 17 Old 07-04-2014
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Re: Blistering

I would grind out the blisters and fill with thickened epoxy as posted. I would use silica and if you are careful there will not be much to sand.

I would not barrier coat the entire hull unless it is proven to be dry. Use a moisture meter with a base line from the topsides. A good drying takes many months.

Brian
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post #10 of 17 Old 07-04-2014
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Re: Blistering

Shinook and Mitiempo, thank you for the quick responses. I liked how
Watertite sounded, but was put off by manufacturer's statement that it must be covered with Interprotect. Doesn't make sense to me, but that is what they said. I don't think I am going to barrier coat this time. Boat is new to me and have no idea what the blistering history is. Prior owner said it had been in fresh water for 7-10 years without hauling out. There are many blisters but not big.

Either of you pre-treat the ground-out blister with thin epoxy before filling? If this is a good idea, I want to use an epoxy that doesn't require washing or sanding to save some effort. Any ideas on brands?

I am good on drying time. Boat will be out of water for 6 months before filling, etc.
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