Bottom paint question - Great Lakes

May 6, 2010
472
1984 Oday 39 79 Milwaukee
Attached is a photo of the rudder on a boat we recently acquired, prior to disassembly for reconstruction. The boat is a 1984, and has always been in the Great Lakes. If you tear your eyes away from the badly delaminated skin and foam core for the moment, you can see that the top layer of bottom paint is flaking off from the layer underneath. The boat has not been in the water since 2016. I don't know when the bottom was last painted, but the last bottom paint is black and the flakes are extremely thin and somewhat brittle. It is definitely not an ablative type paint. When it flakes off, what appears below it (not readily seen in the photo) is bright copper color. Prior to having pieces start to flake off, I would have thought the black was VC17 but I've used VC17 for many years and have never seen it flake like what is happening here. Many of the flakes come off in large pieces of 3 - 4 inches. It seems there was either incompatibility with the previous paint, poor prep, or???

While the rudder had very obvious issues, I don't really notice any areas on the rest of the hull that are peeling presently, but I suspect given the right provocation it may occur elsewhere. I am inclined at the end of the season to sand the top layer off and start over from there but wondering if anyone has experience that might indicate a cause so I can plan a proper solution?

Thanks,
Scott
rudder.jpg
 
Jan 11, 2014
11,321
Sabre 362 113 Fair Haven, NY
I suspect what you are seeing is the original barrier coat falling off. Back in 1984 it was common on the Lakes to apply a VC Coal Tar barrier coat and then the VC 17. Over time the epoxy coal tar becomes brittle and fails.
 
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May 6, 2010
472
1984 Oday 39 79 Milwaukee
bulges.jpg
I suspect what you are seeing is the original barrier coat falling off. Back in 1984 it was common on the Lakes to apply a VC Coal Tar barrier coat and then the VC 17. Over time the epoxy coal tar becomes brittle and fails.
Hmm, that's possible but I'm not sure how to explain the very consistent layer of copper that is exposed when the black flakes off? I would seem like there may have been VC17 (quite possibly applied over tar), and either something else applied over it that is incompatible/failing, or someone did no prep one year before applying the last layer??

I should add that the part of the rudder where this occurred had delaminated so badly that there were very large bulges (see photo) in the fiberglass skin - is it possible the VC17 just let go because it couldn't "stretch" when the skin expanded?

Our previous boat had VC Tar, but then had ablative paint for it's whole life until we bought her. I scraped the entire bottom to gelcoat with a 2 1/2" paint scraper. The 20+ year old tar was fairly brittle, and if I could get the edge of the scraper to catch a hard edge, it would come off fairly well. If the scraper slipped it sort of burnished the edge and it was difficult to get going again. That is a job I would not care to do again.
 
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Jan 11, 2014
11,321
Sabre 362 113 Fair Haven, NY
A couple of years ago I removed many years of VC 17. It was not an easy job. Sanding with anything less than 36 grit just burnished the bottom. Over time, the copper in VC 17 become a copper plate.

The simple test for VC 17 is to wipe an area with acetone. If it is VC 17 you'll get a copper color and it will smear. The second photo sure looks like VC 17.

Another possibility is that some put a hard bottom paint over the top of VC 17. And what you are seeing is the that paint failing. Because VC 17 readily dissolves in most solvents, it is possible to get paint to adhere for a while.
 
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DougM

.
Jul 24, 2005
2,242
Beneteau 323 Manistee, MI
In some respects, that looks like someone tried to cheap charlie a bottom job by applying a less costly bottom paint over VC17. In most cases, the VC17 must be completely removed because other paints will not adhere to it.

As to the comment about successive layers of VC17 building up, I doubt that would be significant. The stuff is really thin compared to other paints.
 
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Jan 11, 2014
11,321
Sabre 362 113 Fair Haven, NY
As to the comment about successive layers of VC17 building up, I doubt that would be significant. The stuff is really thin compared to other paints.
Having spent many hours attached to a sander, I can attest to the build up of copper. In some places, like the leading edge of the keel, the bow, and the rudder, there is enough water movement that the copper wears off. However, in places where there is less aggressive water movement, like behind the keel, the copper builds up. In some places the copper was about 1/16" thick and very solid. It was like sanding a copper sheet. A solvent wash did little except renew the bright copper color. It resisted anything finer than 36 grit on DA sander and the 36 grit was only good for a square foot or so.

In other areas, like the rudder, a quick swipe with 40 grit took the paint and copper right off.
 
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Jan 11, 2014
11,321
Sabre 362 113 Fair Haven, NY

Harlan

.
Jun 4, 2004
99
Oday 34 Niantic
Shifting gears a little. I had a large delamination blister show up on my OD34 about 15 years ago. I called Foss Foam for help repairing and they were very helpful. Final step was to NOT paint it black or any dark color. Foss claimed the heat build up on sunny spring/fall days while the boat is hauled can be enough to cause the blister. (Walking around the yard on sunny days I note the black rudders do get hot.) After repair I painted it white and no further issues - rudder is perfectly dry, no more blisters!
 
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Jan 7, 2011
4,726
Oday 322 East Chicago, IN
I use VC-17, and your rudder does not look like VC17. Too dark.

And VC17 is very thin. Can easily sand it off.

Greg
 
Sep 24, 2018
2,549
O'Day 25 Chicago
This Spring I just found the best way to sand a bottom, Diablo SandNet, 5 inch, 120 grit from HomeDepot.

https://www.homedepot.com/p/Diablo-...plication-Pad-10-Pack-DND050120H10I/301439866
Unlike sand paper it doesn't clog up. You can just keep going and going. I used one 5" disk to sand my entire bottom. You can use other grits, such as 80 grit to strip faster.
I used the 100grit version of this. The velcro would wear out before the paper would clog. What kind of palm sander did you use?

I used sandpaper and TotalStrip paint stripper to remove all the layers of bottom paint and Brightside

The PO of my boat put Brightside over the entire boat. I had some inexperienced friends help me do bottom paint. They painted the rudder before I had a chance to remove the Brightside. It is flaking off now in a similar manner as what Sefuller described but the pieces are smaller. We used Blue Water Marine Coppershield 45
 
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