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post #1 of 6 Old 07-15-2011 Thread Starter
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Steel hull maintenance

Hi. (new to this forum)

I have a 20+ y.o. 13m steel cutter. (Bruce Roberts' Norfolk). The hull was professionally built, galvanized and painted with the Awlgrip system.

It is still in near perfect condition. However I am coming more and more frequently across some kind of paint delamination, mostly on deck. Yesterday I encountered two such spots below the waterline. I am trying to figure out the best course of action.

1) what exactly is happening? Using a needle hammer will remove small patches of paint over maybe 2% of the painted area. There is sometime incipient rust, but usually I see sulfated zinc (i.e. the zinc coating is still protecting the underlying steel, but has been attacked by moisture)

2) what to do? A complete sandblasting is not warranted right now as the wear is limited and the result of an expensive job might actually be worse than the current situation. So it means spot treatment.

I either try to get to bare metal and prime/paint, or passivate rust with a converter such as Ospho, prime/paint.

Two years ago I half heartedly tried the bare metal route. Several patches didn't hold well. So, this year I am attempting the passivation approach.

I know that this is a recurring theme. One can find every kind of opinion. Maybe you can suggest a short list of "definitive" sources.

Main questions are

1) pros and cons of passivation vs bare metal for touch up.
2) zinc/primer adherence. What made the primer lift?
3) a practical touch up system. Awlgrip isn't widely available. I am going for International. I understand that a two-part epoxy primer may be superior to a one-part, but for touch ups mostly on deck, it isn't as convenient.

Thanks in advance for your suggestions
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post #2 of 6 Old 07-15-2011
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I have a friend with a steel Van De Stadt 34 and he has a lot of problems with losing paint due to stray electrolysis leaks from his electrical system. His problems are mostly from losing antifouling however it is probably worth checkning your electrical system to see if you are losing current. This maybe one reason why your primer is lifting.

That said he has a constant battle with rust spots on his deck. I remember once some spot rust showing through within 1 month of totaling repainting the deck.

I think you need to trial different systems and decide what works. I have found International products very good on my fibreglass yachts, however their products are expensive.

Good luck Ilenart
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post #3 of 6 Old 07-15-2011
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I had an ald steel boat which I lived on and cruised for 7 years. The most effective solution to patching was as follows.

Remove as much rust as possible.

Apply phosphoric acid.

Wipe with acetone.

Apply a minimum of 3 coats of zinc rich epoxy 5 or 6 is better. [I used Sherwin Williams.]

Top coat

This was used above and below the waterline.

A small pot of paint with a brush through the lid was used to touch up chips asap.
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post #4 of 6 Old 07-15-2011
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Steel VDS34 here.

In six years we have not had your problem Gauvins but from what I've seen on other steel boats you have an electrical problem. You need to find the fault and fix it or you will have ongoing problems with paint adhesion.

Question .... how are your anodes ?

Andrew B

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post #5 of 6 Old 07-16-2011
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Buy a Dremel tool and lots of metal grinding stones, diamond tipped tools, sanders, etc.

Attack the blisters with the Dremel and go to bare metal. Make it as clean as you can. You'll need to find the edges of the blister where there is good paint-metal adhesion. There will be some pitting and you won't get all the rust, but get as much as you can.

Then treat the area with Ospho or other phosphoric acid rust converter (Turns the FE Oxide to FE Phosphate or something like that). Clean that off and then paint it. Choice of systems is up to you. One is mentioned above, the system I've used for 10 years involves successive coats of Interlux and Alwgrip as follows:

On the cleaned/chemically treated metal start with
Interlux Vinylux etching primer -- one thin coat followed within 24 hrs by
Interlux Interprotect 2000 -- two coats of this 2 part epoxy, then
Fill and fair with a 2 part filler -- Interlux makes fillers for above and below the waterline, followed by:
Your choice of finish paints -- in my case -- sprayed on Alwgrip epoxy primer and then Alwcraft 2000 (which is much easier to "patch" than Alwgrip.)

I usually leave the final two stages (Alwgrip) to professionals, but I'm working up my courage to try the finish painting myself.

I've done patches/repairs this way for over 10 years. Some of my early ones are still perfect. Some I did two years ago are back for another round of repair. I think it all depends on the quality of the prep and whether you got all the rust / oxide treated before it was recoated.

Nothing beats steel for strength, but you do need to be diligent about the rust. Take as much care with the inside as you do the hulll, but inside you can skip the shiny paint finish steps.

PS -- I forgot to mention -- also buy a very good shop vac with lots of suction. Keep the suction going at the point where you're grinding off the rust. Whatever grinding dust escapes the vac hose will find it's way into your non-skid and you'll have lots of tiny rust spots all over your deck.

Last edited by billyruffn; 07-16-2011 at 06:00 PM.
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post #6 of 6 Old 07-17-2011
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Quote:
Originally Posted by tdw View Post
Steel VDS34 here.

In six years we have not had your problem Gauvins but from what I've seen on other steel boats you have an electrical problem. You need to find the fault and fix it or you will have ongoing problems with paint adhesion.

Question .... how are your anodes ?

I think I'll take that back. For some reason I thought you (Gauvins) said 'back to bare metal'. If its only the top coats coming off or blistering then its probably not electrolosys but rather as BillyRuffins suggests simply poor paint adhesion or incorrect paint selection.

Andrew B

“Life is a trick, and you get one chance to learn it.”
― Terry Pratchett, Nation

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