Keel paint failure. Hull is fine. How to proceed?

[ohthetrees]

Hello all, I cruise 9 months a year. Our boat (2015 Hanse 505) is currently on the hard in Shelter Bay Panama. About to head back to the boat, and I'll need to address paint failure that is happening on the cast iron keel, but nowhere else. Would very much appreciate advice on how to proceed with a DIY solution. I'm unsure how difficult and expensive it will be to acquire materials in Panama when I head back in a couple of weeks, so I'm looking for the minimally intrusive solution.



Background: We bought boat with unknown black colored ablative bottom paint. We sanded that well, but not all the way back to barrier coat, and applied Pettit Odyssey HD in 2000 in Port Townsend WA. This paint held up very well. The boat sat on the hard in Puerto Penasco Mexico in very hot dry conditions for summer 2001. When we came back to the boat we lightly sanded with 80 grit making sure to leave nothing loose or flaky. Then we applied blue Pettit Odyssey Triton according to the instructions.



Diving the boat for regular inspections and prop cleanings, I soon noticed that the paint on the keel was failing. Hull paint is perfect. It was sloughing right off, and I could rub it off with a bare finger, getting down to the white (barrier coat? Hard bottom paint?) layer below the ablative bottom paint. I'm wondering whether the heat of the black paint on the cast iron keel in the hot Mexico sun caused the bottom most layer of ablative to fail.


My questions:


1) Given the above narrative, and the photos below, do you think I can get away with sanding down to the "white layer" (barrier coat? old hard bottom paint?) and reapplying bottom paint? I'm really hoping not to have to go down to bare metal.



2) One of the photos shows where the "white layer" has failed and there is a "gray layer" below that. The gray layer appears totally solid and good. This is only in a couple of very small areas. What are these layers? Could the "white layer" be hard bottom paint put on by the previous owner, or does it look more liker barrier coat? Does the whole "white layer" need to be removed before I can proceed?


3) I've included pictures of a couple of "scars" where a fishing line encountered at sea rope-burned through the paint down to metal and there is a tiny bit of rust appearing. How do I address these areas, or for that matter any area where the barrier coat is beached?



4) I've included picture of two dodgy looking areas of the keel/hull joint. The rest looks good. Do I need to pull/grind out all the caulk and redo this joint? With what product? Any links or resources for doing this job properly? Or just paint and get on with my life?



Thanks so much in advance! Many areas of boat maintenance come naturally to me, but this seems like a bit of a struggle.

[JPA Cate]

We have a fin keel that is steel, with the lead poured into it. Throughout our ownership of this boat, we have had a hard time getting the systems right to not have paint blow off the keel. You said your keel was iron. Do you know how it is actually constructed?

In our experience, paint will often crack at the keel to hull join, it just does. It has on the boats since 1983. It looks like there's an epoxy undercoat. After that it needs a primer that is compatible with both the new paint and the undercoat.

Good luck with it.

Ann

[Searles]

Is the bottom of the keel well coated ,with epoxy and or a/f ,any exposed iron os steel may set up a cell with the use of high copper a/f ,also check if the so called earth wire or strip is connected to a keel bolt or a tapped position to the iron keel ,the heat on the black a/f may have been enough to start separation of the surfaces ,check and check again ,.⚓️⛵️

[coopec43]

Is the problem only on one side of the keel (the side exposed to direct sun?)

[ohthetrees]

It is more on the port side, more on the bulb than the rest of the keel, but some on the stbd side of the bulb too. But one side would get sun in the morning , the other in the afternoon, and would already be extremely hot by 10am.

[wingssail]

I would sand the whole keel and bulb down to well adhered paint, but not through the grey which is probably an epoxy undercoat. You will need some epoxy however to recoat those places where metal is exposed. After sanding there may be more of these places.

You may choose to coat with a new epoxy undercoat before painting with antifouling. Use the manufacturer's recommendation if possible

You will need an antifouling paint which will stick to the undercoat. Use the manufacturer's recommendations.

Contact Shelter Bay Marina and find out the phone number of the chandlery there. Ask what paints are available and then verify the compatibility with that paint's manufacturer.

You may be forced to accept whatever they have and hope for the best because carrying 5 gallons of paint on the plane will be difficult. You could possibly ship it ahead of time.

I ran into these difficulties while cruising. I simply used what was available. I had flaking paint on our keel every time we hauled out. I just repaired it as best I could and carried on.

Regarding the hull to keel joint, I would ground out the cracking fillet and replace it with epoxy filler, then fair it smooth before painting.

[MicHughV]

Here's my 2c.

Water has gotten in behind the paint and lifted the paint.
How the water got there is anybody's guess.
Impact, anchor line or chain dragging against the keel, lousy prior bottom job, etc....could be any reason.

My advice, chip the paint away around exposed edges, until it's not possible to chip anymore, as the water may have intruded past what is visible now. Clean any barnacles, etc. Then a good sanding to give the keel surface some teeth for the new paint.

Once done cleaning, allow the keel to dry. Coat the keel with a good two part epoxy paint that will attach to metal, any color will do. Prior to the epoxy paint, feather the existing paint edges back about 2" or so with sandpaper on a wood block or use rotating grit disc. Make sure the epoxy paint overlaps the existing feathered edges. Apply a second coat, even a third coat to build up the paint thickness. Sand the final coat.

Once the last coat is dry and sanded, apply bottom paint as per usual.

[ohthetrees]

Thanks everyone for your thoughts.

Can someone clarify the difference between barrier coat and epoxy paint, and when I would use one versus the other?

If I get down to bare metal in some places do I need a metal primer (I’ve heard of people using zinc chromate on cast iron. Maybe?) before I use epoxy paint/barrier coat?

MicHuhV if I follow your advice, do you mean to chip down to the apparently solid gray layer, or down to metal?

Thanks!

[wingssail]

Originally Posted by ohthetrees

Thanks everyone for your thoughts.

Can someone clarify the difference between barrier coat and epoxy paint, and when I would use one versus the other?

If I get down to bare metal in some places do I need a metal primer (I’ve heard of people using zinc chromate on cast iron. Maybe?) before I use epoxy paint/barrier coat?

MicHuhV if I follow your advice, do you mean to chip down to the apparently solid gray layer, or down to metal?

Thanks!

I cannot tell you specifically because I am not a professional at this type of work, just a DIY boat owner with a lot of years experience on several boats. I recommend you check with a pro at the boat yard.

But anyhow, barrier coats are often epoxy paints meant to keep water out of the underlying material, often fiberglass gel coat. They are usually 2 or more layers thick. So the epoxy used to cover a portion of the keel may be similar but the application is different.

For an iron keel probably a metal primer is a good idea. Iron is notoriously hard to paint. But for small areas if it is roughened and clean, I think epoxy will do fine. (just my view). On my lead keel I have never used primer, and often have painted small areas (less than a foot square) with epoxy, often not even epoxy paint, just with epoxy filler. It seems to stick. Clean and rust-free is important so apply whatever you use immediately after cleaning it, before any oxidation starts.

[Franziska]

An old trick is to use sandpaper to briefly sand the epoxy into the metal surface right after application while it's still not cured.
That way you do not get oxidized areas under the epoxy.
Add a second layer of epoxy thereafter.
Try it on some other metal before to get your technique.

Use gloves!

Good preparation and cleaning before the epoxy is applied helps as well.

[Searles]

Barrier coats in this part if the world are normally coats to seal one type of coating I/e anti fouling when changing types or brands,epoxy’s are used as base coats over correctly prepared surfaces usually under water ,many coats wet over wet I/e semi cured topped off by hi build epoxy ,much information is available on this subject ,it varies from country to country .⛵️⚓️

[MicHughV]

I can't quite tell the issue with the rust as I see it in only two spots.

Nonetheless, there are various products on the market that can "nuetralize" the rust...Ospho is one brand. but other's are likely to be found in your area. If you see any loose rust, chip or sand this away and just paint the Ospho over the rust and let dry. The rust should turn black.

There are a variety of barrier coats to be found. I don't think it is necessary to use a zinc primer, as other than the two spots, I don't see any need for it.

I like to use the two part epoxy paints, as they get get really hard. The idea is to build up a several layers to provide a "protective" layer. As suggested above, put the first layer on, and before it gets very dry, apply the second coat, so they can bond with each other. Repeat with the third layer. Don't forget to "feather" the edges of the old paint surfaces. The whole point of the barrier coat is to keep air and water away from the keel.

It will be tricky, but make sure the epoxy paint extends to below the keel wings. Dig away the dirt to allow a brush to get in there.

Paint manufacturers usually have a "system" of paints that are compatible with each other, so try to find an epoxy paint that will be compatible with the antifouling paint.
This is not a deal breaker if you can't find it, but it is preferred.

[Rumrace]

I’m still a little confused on the photos and comments. If it’s raw metal I’m seeing I’d use an iron oxide primer from DuPont before I discussed what wonderful thing the marine industry decided to add. I’d put two thin coats wet sand two thick coats wet sand and a final tack coat. I wouldn’t use any copper on zinc based paint on top of it. Cream white imron and some ugly black bottom paint is more likely. Or Prop and Drive paint after the cream white. I’d bake in with heat lamps

[Bilgediver]

Originally Posted by ohthetrees

Thanks everyone for your thoughts.

Can someone clarify the difference between barrier coat and epoxy paint, and when I would use one versus the other?

If I get down to bare metal in some places do I need a metal primer (I’ve heard of people using zinc chromate on cast iron. Maybe?) before I use epoxy paint/barrier coat?

MicHuhV if I follow your advice, do you mean to chip down to the apparently solid gray layer, or down to metal?

Thanks!

Some paints are not compatible and what you show could be the case here. If this is the case then you need to try a tie coat on the lighter coloured surfaces before repeating. fortunately there are coatings which make good tie coats and also ideal for treating the bare steel or cast iron following sand blasting. International Paints have a product called Primocon and they have an office in Panama.

Their website is as below and could be worth a call as they would have a technical team in a place like Panama

https://opencorporates.com/companies/pa/403520




https://opencorporates.com/companies/pa/403520