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Old 08-02-2009, 10:16   #1
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Blisters and Pocking, Oh My!

When we hauled OWTW ('85 Baba 35) last fall, I had the bottom soda blasted to remove all of the bottom paint, which had begun to flake off and was generally getting pretty lumpy, even though we use Micron Extra (ablative) paint.

I've been aware of osmotic blistering for a while (5+ years?), but felt that it wasn't a major issue. Until the soda blasting showed some surprises.


In addition to the osmotic blistering, there are large patchs of pocking. Up close, it looks like this:


The big question is: do I just fair this mess and seal it with epoxy (the hull's thick enough that the existing blistering isn't even remotely a strength problem) or does it need (that its, not just, "well, it'd be nice to do it" or "it couldn't hurt") to be peeled?

I don't know what all of the layers that cover the fiberglass are. I know the boat was coated with Bar-Rust (two-part epoxy paint used to seal steelwork - applied by Tiffany Yachts near Reedville, VA) before the bottom paint was applied prior to our purchase of the boat ('93). I assume this is the light colored top layer. Of course there should be some gel coat on the hull, but whether Ta Shing (builder) added any other coatings or any were added during commissioning (by Annapolis Sail Yard in '85-'86) is anyone's guess.

Finally, I'll call Peter Hartoff in Annapolis to arrange for a hull survey - might as well have one paid opinion in hand.

Click HERE for a link to an album of three images of the bottom.
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Old 08-02-2009, 10:32   #2
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I don't think I would peel it. The bigger question is the moisture content. If you could get some readings it might help to make sure that when you start the restoration you don't trap high levels of moisture inside the hull. The blisters can be ground out before filling. They look to be dime and quarter size more than grape fruit size.

Given the age of the boat it's pretty clear this isn't a huge disaster. It's more a cosmetic problem that used to be covered in barrier coat. Getting it dry, then filled, and faired would make it look a lot better and hold up a good long while. The fairing is probably the worst job. Bottoms get a lot bigger out of the water when you have to deal with it on an inch by inch basis.
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Old 08-02-2009, 10:47   #3
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Well, that is a comfort.

In the past, we've hauled the boat roughly every two years and let her dry out for the winter. By the time it's warm enough to wax the hull, the blisters are basically gone (well, flat, anyway). At the time the photos were taken, OWTW had been out of the water for about two months. Whether the cold weather has anything to do with the glop in the blisters drying faster or not is anyone's guess. Unfortunately, the way the boat's sitting the starboard side is facing roughly north and won't get much sun. That may or may not make a difference. Anyway, the stuff does flatten out over the space of 4-5 months.

It's the pocking that's really puzzling me, as it seems to appear in patches all over the hull (such as forward of the well for the port hull zinc)., although most of it is closer to the waterline than not. [/headscratch]
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Old 08-02-2009, 10:53   #4
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it's definitely pretty wet and pretty common. It's a comment that now matter how good the boat yard, they really dont know (didnt know?) what is causing the blistering. My Passport 47 was bistering bad (ta Shing) My Hans Christian 38 was also, my Rawson 30 had huge ones, My Ta chaio built 44 didnt have one blister. I had the Hans Christian peeled in Trinidad and then let it dry out for 4 months (is that possible in Trini? ;>) The job came out nice, but it would be huge expensive int he states... a lot of work involved after peeling. Do you see blisters in some of your bilge areas? if you break a blister with a sharp object, does it bleed a lot?
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Old 08-02-2009, 10:58   #5
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I agree with Paul...Drying it out would be the best bet. I am assuming you are in cold climate where drying may need to be done with lamps this time of year. If the boat has been dry docked for awhile, you are in better shape but I still think you need the lamps. Perhaps use an epoxy fairing compound. Awlgrip makes a good one that is very sandable. Then I would use Interlux 2000 and finally your choice of bottom paint.
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Old 08-02-2009, 11:02   #6
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I think Paul is onto something with the moisture content. In my opinion if you put epoxy over the wet hull it will blister again. Soda blast or peel regardless. The boat yards out here in SD are no longer giving any type of guarantee with just a epoxy over a wet hull. The process that they are guaranteeing is to peel the laminate to a depth that the moisture content is acceptable then apply laminate with vinyl ester resin building back to a pre peeled thickness. I have seen it done numerous times, very expensive and looks extreme. This peeling that is done is because of the time it would take for the bottom to dry. If you can find away to let the bottom dry that would be best. Because the soda blasting has removed so much of the gel coat you are going to have to do some sort of rebuild. The reason the yards are rebuilding with vinyl verse epoxy is that the vinyl will allow some moisture to move out. If I you are doing this work yourself maybe you can lay the boat up long enough to allow it to dry. If you can avoid compounding the problem...I guess thats stating the obvious.
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Old 08-02-2009, 11:07   #7
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I would definitely use real epoxy resin first, I'm not a believer that the Interlux will provide a good enough barrier. You need to time the first primer or bottom paint after the epoxy so you dont have to sand the epoxy! Any yard hand can give you the details. All the boats I mentioned were done that way and held up for survey when the boats were sold later...
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Old 08-02-2009, 11:16   #8
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Originally Posted by Cheechako View Post
I would definitely use real epoxy resin first, I'm not a believer that the Interlux will provide a good enough barrier. You need to time the first primer or bottom paint after the epoxy so you dont have to sand the epoxy! Any yard hand can give you the details. All the boats I mentioned were done that way and held up for survey when the boats were sold later...
Real epoxy??? Interlux 2000 is a 2 part epoxy formulated just for barrier coat.
Interprotect 2000E Epoxy Barrier Coat Kit, Grey from Wholesale Marine

I used it in 1988 on a 34 ft boat I use to have and I saw it last year. The owner told me it was blister free.
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Old 08-02-2009, 11:41   #9
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Sorry, didnt mean to light anyones fire. I'm sure it's a good product, probably the most heavily used commercial product out there. Definitely better than nothing on a non blister or new boat. I had a boat that had about a 6 foot stip of blisters near the water line. The yard ground out and fixed the blisters and then coated the boat with the interlux prior to painting. The blisters were back the next year at haulout. This boat was not as severly blistered as any of the boats I mentioned above. They all survived 2-3 years before selling. Just my experience. The Interlux has more the consistancy of paint, so some yards can spray it. The Epoxy is a sticky mess with limited working time and yards prefer to use what's easy. I've had over 100 new boats coated with the Interlux in my previous job, there's no way my bottom guy would have wanted to roll on Epoxy resin...
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Old 08-02-2009, 12:44   #10
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The Bar-Rust coating was put on before we even saw the boat (PO had it done). We talked to Tiffany Yachts about the job and they seemed to know what they were doing. Tiffany is mainly a power boat operation, building as well as maintaining boats - they have a reputation for building higher end boats, so one would think there yard work might be about as good. The PO kept the boat at their yard, AFAIK. Past that... eh, it's now at least 15 year old news, so who knows what really happened.

Part of the reason for having Hartoff survey the bottom is to get real moisture numbers. Unfortunately, heat lamps are not an option at the yard where the boat is. Not unless I want to run my own service and meter... don't think that's going to happen.
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Old 08-02-2009, 14:35   #11
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If you are just going to dry it out it may take a while. We did a Taiwan trawler here about 2 years ago. It took all summer to get the moisture level down low enough that they could get the warranty. The ambient humidity in the summer can be so high that it won't dry. They have been doing some with vacuum panels that basically lower the boiling point enough to dry out sections at a time. It's usually done in a shed.
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Old 08-02-2009, 15:23   #12
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Interesting. I had not bought a "Blue Water Sailing" magazine in years and just picked one up the other day. It has an article on blisters. It may be worth a read.
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Old 08-02-2009, 16:09   #13
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Sorry, didnt mean to light anyones fire. I'm sure it's a good product, probably the most heavily used commercial product out there. Definitely better than nothing on a non blister or new boat. I had a boat that had about a 6 foot stip of blisters near the water line. The yard ground out and fixed the blisters and then coated the boat with the interlux prior to painting. The blisters were back the next year at haulout. This boat was not as severly blistered as any of the boats I mentioned above. They all survived 2-3 years before selling. Just my experience. The Interlux has more the consistancy of paint, so some yards can spray it. The Epoxy is a sticky mess with limited working time and yards prefer to use what's easy. I've had over 100 new boats coated with the Interlux in my previous job, there's no way my bottom guy would have wanted to roll on Epoxy resin...
You didn't light any fires man...I just thought maybe you felt I was referring to Interlux enamel or something. Like you say different experiences. I have seen people use west systems laminating epoxy but they have to add cabosil as a thickening agent so it does not sag when applied. Definitely regular epoxy would go on thicker, so maybe that is the way to go. When I get blisters again (not if...when) perhaps I will try your way.
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Old 08-02-2009, 18:57   #14
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We had the EXACT situation with our 28 foot sloop. Shallow pox with high moisture readings.

We did a gelcoat peel including the outer layer of finish glass. Following the peel, moisture readings dropped to zero. We let it sit over winter. To put back in, we coated with West Systems straight epoxy (really mushed it into the hull). Followed by five coats of Interlux 2000.

Our cored hull was thick enough such that we did not have to replace the layer of finish glass that was removed.
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Old 09-02-2009, 09:32   #15
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A thin peel and drying time is definitely the best fix and should help at resale time too. Then again, boats ain't perfect and it will still get you where you want to go!
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