Paint Advice Needed for Galvanized Steel

[sigrid]

Hey sailors and painters J

I have a nice steel mono hull 35 ft Van De Stadt sailboat named Lucky Bitch. I left Belgium (NW Europe) last year, single handed, and my plan is to sail her around the world. Therefore I plan about 8 years.

Now I am hauled out in Chaguaramas, Trinidad, Peakes to work on the boat. The underwater ship and keel have a paint problem. Paint peels always off, since I came in tropical waters and sail almost constantly.

Last February 2012 I put 2 layers of Primocon Primer on it and then 2 layers of Micron 66 Interspeed Anti fouling, light blue. Now, lifted out the water, I almost started to cry: the paint just peels of!!!!!

The steel of my ship is in good condition – no rust. There is a layer of zinc on top of the steel outside, under the waterline. It is shooped (thermisch verzinkt we say in Flemisch) so it is galvanized steel.

I am desperately seeking for a GOOD LONG LASTING DEFINITE SOLUTION for this peeling of problem, so that I only have to repaint with anti-fouling ONCE in a year.

Off course here I hear different opinions of different (paintsellers) people…

A:
Some say absolute get rid of the zinc, so sandblast and do away with the zinc layer, to the blank steel, because, as they said, the sink is a stupid very bad idea, a wrong thing???

B:
Other say, absolutely NOT remove the zinc layer. Because it has a very good protecting function. Just find a GOOD etching primer to put on (in a correct way) the sink, to create a perfect adhesive surface.

So, readers, sailors, advisers, you can imagine I am a little bit confused.
Because I want to care really for my boat, sail her longtime, not waste useless money and time on her, I like to find more advise, opinions. Experience with the same challenge would be ideal.


Hope to read you soon and find out?
Sigrid Greven, skip SY Lucky Bitch, Chaguaramas, Trinidad.
www.luckybitch.be
lbgoesaround@gmail.com

[Sailmonkey]

Painting zinc is a bitch (pun intended). It will need to be etched with something like ospho or other similar acid to get anything to stick to it, then it's a crapshoot. When the zinc does it's job it gets chalky......
I'd tell the guys that want you to sandblast the zinc off to go somewhere else.

[nonam]

Keep the zinc.See if you can find any primer paint which acts like a glue.Several years ago I used to commission new sailboats.We were always worried about mould release wax in the new gelcoat preventing the antifoul paint from sticking.After wiping the hull with solvent,we applied a Zspar primer before we applied the Zspar antifouling.
So I assume you did apply the primer recommended by the manufacturer of the antifouling paint that you used?
If you decide to etch the zinc with Phosphoric acid,be careful and quick as it can eat right through your zinc.After etching,I would put on a high build epoxy barrier coat.When cured,I would sand it and apply a primer and then the antifouling.

[barnakiel]

It is very difficult to remove paint layers without damaging the zinc layer.

If you decide to blast it (I would not hurry) remember Trinidad has humidity and you will have to work in sync with the blaster to immediately apply the first epoxy coat.

If the zinc is in good condition throughout perhaps you can remove the old paints with a chemical stripper then wash the boat very, very well (powerwash) and apply a zinc compatible primer? Antifouling and topcoat will stick very well to the primer then.

b.

[sigrid]

Thanks for this adivice already, I think to go with plan B: KEEP the zinc.
All CONCRETE marks, branches and types of paint, stripper produkt, primers, epoxy coating are also welcome.
what is crapshoot?

bye
Sigrid

[Sailmonkey]

Originally Posted by sigrid

what is crapshoot?

bye
Sigrid

It's a slang expression meaning that sometimes you get lucky and all goes well, or it doesn't. No planned predictable outcome.

Although I suppose there's a little more science to painting zinc that would make it a little less on the luck side and more on the skill and knowledge side that will prevail.

[barnakiel]

Originally Posted by sigrid

Thanks for this adivice already, I think to go with plan B: KEEP the zinc.
All CONCRETE marks, branches and types of paint, stripper produkt, primers, epoxy coating are also welcome.
what is crapshoot?

bye
Sigrid

I am not into chemistry so PLS consult with a chemist before you proceede.

This much said, have a look at this source as it may relate to the job at hand:

http://www.dtic.mil/dtic/tr/fulltext/u2/a454138.pdf

Personally, I would look for a brand epoxy primer compatible with zinc. Try International paint catalougue.

Cheers,
b.

[mrm]

Originally Posted by sigrid

All CONCRETE marks, branches and types of paint, stripper produkt, primers, epoxy coating are also welcome.

Many years ago (25+) I had to paint a zinc coated steel structure. At that time I was advised to use a yellow chromate etching primer on Zinc to get subsequent paint layers to stick. So far that advice seems to work very good, so I pass it along...

[minaret]

Blast clean to the zinc, acid etch, zinc chromate heavily and sand to a finish. Then apply a few coats of Interlux 2000e, then chemical bond the bottom paint to the 2000.

[nonam]

Do you mean water blast?Do you sand the zinc chromate to fair it or to get a rough key for the next coat?2000e is a barrier paint?How do you chemically bond the bottom paint?Put the bottom paint on before the 2000e is fully cured?

[minaret]

Originally Posted by nonam

Do you mean water blast?Do you sand the zinc chromate to fair it or to get a rough key for the next coat?2000e is a barrier paint?How do you chemically bond the bottom paint?Put the bottom paint on before the 2000e is fully cured?

I would suggest soda blasting, though you will need a very skilled operator to remove the coatings and leave the zinc intact. Alternatively you can chemical strip, but blasting does leave a nice profile. Immediately acid etch with Interprime 539, followed by several coats of sprayed high build zinc chromate. Sand to a 180 profile and apply 3-5 coats of Interlux 2000e with a 1/4" nap candy striper. Then chemical bond the bottom paint to the 2000 by carefully following the instructions on the can (use the thumbprint test). You will get an excellent bond this way, and the barrier coat will be thick enough that if you ever have to sand off the bottom paint again it will be easy to sand to the barrier coat and stop there, hence no more etching. If you fair in zinc chromate as well, which is very common, you will probably blow through all over the place and have to re etch and re prime. I believe you can skip the zinc chromate and apply 2000 directly to steel, but not sure about flame sprayed zinc. I never do this anyway as the chromate is good for fairing and some is inevitably needed. It is cheaper than 2000 and sands a lot easier as well.

[HopCar]

I think your problem was the Primocon. It should be put on bright blasted metal. No where in the data sheet do they mention it being compatable with galvanized steel. I think you might have better luck with the following Pettit product.

Pettit
Rustlok Steel Primer 6980

Exceptional adhesion to all ferrous metals also including steel, cast iron, galvanized and stainless steel
Wets, seals and adheres to firmly attached rust
Dries rapidly allowing multiple coats in one day
May be applied at temperatures down to 10°F

Rustlok Steel Primer 6980 is an easy to apply, moisture and corrosion proof primer for use on all cast iron and steel surfaces, including galvanized, stainless. Its water impervious barrier offers excellent adhesion and corrosion protection even over rusted surfaces. Recommended anytime an easy to apply, anti-corrosive barrier coat is desired.

Use 120 thinner.

[roverhi]

Unlike aluminum, zinc needs an oxide layer for paint to stick to it. Best to let it sit out unfinished and weather for a couple of weeks before painting. If you don't have the time for that, believe an acid etch wash will do the trick as well. Might look at POR15 as a prmer coat. It loves to stick to steel and is as hard as a rock and very very hard to scrape through in the event of a grounding or collision.

[barnakiel]

Originally Posted by nonam

Do you mean water blast?Do you sand the zinc chromate to fair it or to get a rough key for the next coat?2000e is a barrier paint?How do you chemically bond the bottom paint?Put the bottom paint on before the 2000e is fully cured?

If I remember well, this is the case withe 2000e. In any case just look up spec data pdf on their site and the info is there - compatibility and application methods.

b.

[nonam]

I would try to find a really high pressure water blaster.If the paint is coming off in patches then you can blast the edges and unpeal the remaining paint.Anything that wont come off really is bonded so maybe leave it there even if it gives a rougher bottom.