Keel coating ideas

[Mlp48]

I am helping and advising the owner of a 7 year old 30' daysailer with a fin keel that will not hold onto paint or primer. The baring problem is not over the whole of it but here and there and in the same spots annually. I've have used both Interlux and Petit barrier coats and tried Primocon. I was thinking next of using something "__ lock" but I asked an on-line posting surveyor about this, and he's said, "Wait. There must be an electroloysis problem". I was asked also about possibly having no galvanic isolator or having a malfunctioning one yet this boat has neither because it has no shore power means. The boat has a Yanmar saildrive (aluminum case; bronze propeller, zincs replaced annually) and a Jefa rudder (aluminum shaft and framework) so there's a mix of metal overboard. I bought a test device from Boatzincs.com to see if the boat was protected by both prop and hull zincs and it "read" as it was supposed to. The boat stays on a mooring where growth can be amazing, even though this is the Mid-Atlantic. We have used Trinidad SR(copper paint) on both bottom and keel except near where the rudder enters the boat ANY IDEAS of what to try or do next ?? THANK YOU.

[Cheechako]

I assume this is a bolt on iron keel? If so, you need to sand blast it well and prime it immediately. Then coat with a good metal paint before bottom paint. If it were me I would use industrial Rustoleum.

[Mlp48]

It is a lead keel with some light filler here and there. I was thinking of using something like the coating you've mentioned, after I have removed the anti-foul. THANK YOU

[hellosailor]

Whether it is an iron or lead keel (please do confirm just what it is) some folks would go beyond "immediately". Apply the primer over a freshly cleaned surface, and then "scrub" it in with a wire brush, so that you are literally abrading the metal under the wet primer, leaving a bond with no oxygen contamination.

It is possible that some incompatible bottom paint was used in the past, and that traces of it are still in those areas. Even less likely, is that somehow a silicone "polish" tainted them. Regardless of what the contaminant is, that's what it sounds like.

As it says on the shampoo bottles "Lather, rinse, repeat". And I'd use the wire brush "through" heavy primer, it certainly can't hurt. Except for cleaning out the brush.(G)

[Mlp48]

The keel is lead, bolted-on and faired-in. The keel's source is unknown but the boat was finished and then delivered with Micron 66 as its antifouling. That coating is salinity sensitive and as the boat was moored in an area which had endured a number of tropical storms (which reduced salinity), the paint "cornflaked" -- which is to say it shrunk and pulled away. Micron's manufacturer knew the term but denied it had ever happened anywhere any-time before this event.

[hellosailor]

Cornflaked? As in crackle up in patches, as mud does on a sun-baked lake flat?

When I've seen paint do that, it is always because the primer and main coat were simply incompatible, and the top coat shrank and pulled away as it cured. I'd guess that's a matter of surface tensions and other "invisible" but real physical differences.

FWIW.

People in assembly plants have been known to grab the wrong can and put on the wrong paint or primer. That stuff happens. Happens if a dealer hiring cheap new help does the painting, too.

Heck, in the house painting business, painters have literally been buying Benjamin Moore (an expensive brand) and then keeping the empty cans and refilling them with cheap paint for the next job! It took BM quite a while to figure out why "their" paint was failing. From that cheat.

[Cheechako]

OK Lead. I would sand it bare with rough paper, like 60 grit maybe, then paint it. But read up on lead, there may be special paint for lead.
Reportedly lead expands and contracts a lot. It also oxidizes a lot. So you need real flexible paint. So I would forget about the Rustoleum I mentioned for cast iron. Either way it sounds like you should use soft bottom paint on it also. Best may be to just use the soft bottom paint and the primer recommended for it.

[Mlp48]

You may be very right with that summation -- the "top coat shrinking".

This showed up on "The Hull Truth": 66 is a self polishing antifouling which reacts with salt water, generally meant to stay in all season. Also if the canal you are in is somewhat brackish then the 66 will be even more inclined to corn flaking issues

I am sure there is lots more. While the Interlux rep was telling me he'd "never seen it", I found out they were paying for the re-do of the bottom of a 100 'sailboat which had 66 and then corn-flaking after being docked in a saltwater river but near the site of a fresh water outflow.

It is otherwise pretty good paint if the salinity is right and I forget now what's the limits are, maybe no lower than 10 ppm. It didn't notice anything about it until the boat was hauled. After about a week ashore.. there it was. Grrrrrrr

I don't think this is the problem -- here. and NOW. I took every bit of the 66 off the boat and more... , then re-barrier coated it.
The dopey rep gave me, as a replacement for our removed paint and trouble, a bucket of Pacifica. It grew oysters !

So that came off and and I re-barrier'd it again. This is what we think of Interlux products: .

You know, we might have "understood" had someone been forthright about it !!! Sad thing, that same liar has moved onto a job with the competitor and he will likely lie there as well.

[hellosailor]

Lead ain't that easy.(G)

When you sand lead, or anything else, the sanding actually embeds the contaminants into the "valleys" it cuts into the metal surface. So before sanding, you need to solvent wash the surface to minimize that. And then, some companies will also tell you to solvent wash AGAIN after sanding, to remove any contaminants it has newly exposed.

Also, lead forms a protective oxide coating almost as quickly as aluminum does. Sand it today, paint it tomorrow, and you've got an oxide coat interfering. The alloy and the environmental conditions will determine just how fast, but that's why others say to wire brush the lead surface--after the primer is on it. To eliminate that possibility entirely.

Personally, i'd rather spend the extra time on "you don't need that" prep work, than have to redo the job because I really did.

[Mlp48]

I know you must be right. I have done the same thing with epoxies and added material but "sanding them in" rather than "wire brushing them in". It worked !

[Mlp48]

After sending this same question to Petitt, I had a callback from one of their experts. It was long and cordial and interesting conversation. The expert's main point is that lead is porous and even trapped water could cause the issue. He concluded that it is most likely contamination and not electrolysis -- and suggested trying to drive that out with 'light heat' and following that up with thinned barrier coatings. He said, "That might not "get it'.. but take heart.. I think you're headed in the right direction". Love Pettit !!

[hellosailor]

Lead is porous? Especially molten cast lead?

How nice to know that someone is hiring quantum physicists, even at a coatings company. From their point of view all matter consists of something like 99% empty space, so I guess "porous" is a valid point of view, depending on how you define that word.(G)

I think "contaminated" might be a better word. We used to have lead pipes, lead lined sinks, lead for all sorts of purposes in chem labs were "porous" was not acceptable. But considering the variety of sources for lead scrap...I'd vote for "contaminated".

You could always hit that area with a torch, melt away an inch or so of the suspect metal, and then re-cast fresh lead into the area. That's how auto body work used to be done, you form a clay dam over the area, pour in new molten metal to fill the gap, then remove the clay and file it down after it has thoroughly hardened.

Or, apply a good epoxy barrier coat over that area. Adherence shouldn't be an issue after that.

Porous....I know, it is just the weak electrostatic force that prevents my feet from sinking into the floor when I get out of bed, but still, I don't call the floor porous.(G)

[Cheechako]

If they'd just cast that lead with enough Tributyl Tin in it you wouldn't need bottom paint!