Rust bubbles, penetrating epoxy, and acid etching of steel hull

[bsurvey]

get some belzona. it has many prodcuts and is used in nuclear power plabts for pitting. it is a step up from epoxy

[SabreKai]

I've been working on my 1978 Roberts Offshore 38 for the last few years. I got her sandblasted by a pretty useless company last year and they couldn't get through the original epoxy coating. In a few spots I found rust pores, which were apparently covered over when they build the boat. The pores have epoxy in them, and the photos of the build show it going from raw rough steel to completely painted with no intermediate pics. Kind of odd when they were meticulous in showing every step before and after the painting.

Anyway, I sanded down the really stuck on epoxy and have been painting her with Amerlock 2/400. I know several boats that use it without problems. The nice thing is that it will cure down to -6F. So, I scrap the worst off, then hit it with a needle scaler. Wash down with laquer thinner, and paint. So far it seems to be working well. Odd though, Dulux now sells the stuff and when I picked up a new batch they got all twitchy when I told them I was using it under the waterline. Apparently PPG has backed off on its use for that.

Be advised that a needle scaler will not remove all the rust. It removes paint, loose rust, scale and other crap including hardened roofing cement used to stick down the styrofoam insulation. But it does leave a fine film of rust on the surface by beating the pits and ridges into a uniform height. So perhaps blasting after words might be an idea. I'll let you know in a few weeks. Im about to get into the interior cleaning and that will take all winter.

Oh yeah a word of warning. Wear earmuffs when using the beast. It's like sitting inside a drum. Between the gas compressor on deck and the scaler pounding the snot out of everything, it's pretty awesome.

If you are interested, check out my blog. Start at the bottom and work up.

[Aloha_float]

I would look at International or Ameron - International has products specifically designed for marine environments inclusive of prep, prime top-coat procedures. They have ABS/DNV/Lloyds certified products and are well known in the offshore marine industry. They are likely available locally.

[phipseml]

Hi everybody,

Thanks for sharing your experiences and thoughts. I think I get the picture.

What I was mainly thinking of doing is to fix smaller rust patches as they appear, both inside and outside, but all above the water line. And this is by far not to keep it look shiny, but to keep the structural integrity at a maximum so the boat will last long!

The boat looks fine as it is, no to almost no rust visible anywhere. Having said that, the inside is well insulated (essential for living in the far North) with closed cell foam and styrofoam, so except in the bilge we can hardly see the hull from the inside. Any ideas of what we can do about that, or is it just to either make a huge job and take the whole insides out, or is it just to trust that a good job has been done at installation of everything? The builder is a carpenter by profession (and the insides accordingly high quality) and has done everything twice (since it sank once), so I assume he has done a good job. And do you think if there was any rust hidden behind somewhere, that potential condensation water running down to the bilge would show that by being colored?

Except where we chipped of some paint with the anchor far above the water line (which I fear will have to stay naked until next summer), the only rust we found was under the prop shaft (where we chipped off paint in the most ridiculous way), where there seems to be a quite thick steel plate welded in (stands out about 1cm), which we tried to fix with what we had and could use in that small space: Dremel, rust remover product, and old international epoxy which came with the boat and is surely gone bad (was in the boat the whole winter and likely froze and thawed a lot) and which we applied at below 5 centigrades, three layers on now. We'll see how it holds up! It's an area which we check regularly, anyway, and it's another color than the surrounding now, so any sign of bubbles and we'll redo it next summer with a better method.

I found the name of the builder and will call him up when I find his number to check how he treated the steel. The boat is from 1988, but apparently sank (funny story, or not) and has been stripped and repainted in the mid 90s. From what you write, it might have been zinc galvanized or similar, since there is no rust visible anywhere. But we'll see, maybe the sellers did a good job in fixing rust as it shows up. I don't trust them too much, though, they introduced a couple of questionable to dodgy solutions in other parts of the boat (I'm talking engine and electricity stuff!).

I do suspect rust under the glued on anti slip mats which are all over the deck and likely retain water in areas where the glue didn't hold up. We would like to remove those in the long run, but do get ready for it being a larger job, so we'll do that during next year's haul up and might have a friend with a compressor and experience ready. Then we'll also check underwater...

I liked the reasoning of one of you mentioning that softer or more flexible paint will keep the rust bubbles smaller when painted over - makes sense, and in that context is likely the cheapest alternative for small repair jobs above the water line. I found a product called Hammerite, which has a rusty metal primer and all, but am sure I'll find other non-marine enamels in other hardware stores. All you other using hardware store enamel seem quite happy with it, too, so I think that might be a good way to go for us. I also checked "The Long Way", and if Joshua manages with that, then our Kiwi will also survive!

I am in contact with a sales person at PPG to see what he can do to supply Ameron, which you also mentioned seems to be very good. We'll see how it goes. If not, I will have a look into other systems available here, and will also look into zinc rich primers. Hempel and International are both brands which are available somewhere in Norway. I did read, though, in the DIY book, that zinc primers are hard to attach to the steel and is therefore better not to use them when repairing smaller areas. Any thoughts about that?

The most important seems, though, that the rust is removed as much as possible with whatever is needed to do so. When we worked under the prop shaft, we realized that it is indeed not so easy to do that. It was probably a bad place to start - hunched over and everything - but removing small rust in crevasses without removing steel was almost impossible. So I guess an acid wash is not such a bad idea.

Cheers,
Phil

[Glenn.Brooks]

You might look at using Ospho to prep the metal surface of any repair. Ospho is a green liquid, mostly consisting of phosphoric acid. The phosphoric acid reacts with iron oxide (rust) and changes the rust to iron phosphate- a nice, inert, base coat that can be painted over with all sorts of marine paints. This is an "acid etch" you mentioned earlier. If no rust is present, the metal will turn blackish and remain wet for several days until the Ospho evaporates or is washed away. You can rub it down or dissolve it with thinner to quicken the drying process.

If rust is,present, the chemical reaction will render the rust into a hard gray, inert coating within 24 hours, for which you can prime or paint directly, as you choose.

I've used Ospho for maybe 40 years on boats and never been disappointed in its rust removing properties or as a prime coat to other kinds of paint.


Sent from my iPad using Cruisers Sailing Forum

[hpeer]

I made a long post above about sandblasting, painting, then blisters.

We splashed the boat and she was in the water for about 10 weeks.

When hauled I now have areas on the hull with small, dime size blisters.

Clearly some osmotic process as they have water in them.

Drives me crazy. Most of the hull is fine, but there a few areas where these buggers are. And the odd one here or there.

Very discouraging to go through the whole blasting, painting process and not have it 100% successful.

Plus now, once I strip and repaint these areas, I'll want to pull her again in three months time to see if they have come back yet again.

Piss.

[TeddyDiver]

Google: epoxy tar boat paint

[hellosailor]

hpeer-
Since Ameron is now part of PPG, I'd suggest contacting them to find out what they think along the lines of product failure. Could be an application issue, could be a bad batch of primer. But it sounds like you did the prep very diligently, which means product failure has to be considered. Who knows, they might make good on it.

[hpeer]

I did talk to a couple of their gurus when the issue first came up. They were no help.

One guy could not seem to grasp the concept that the boat was not in the water and had not bee since blasting.

They both frowned upon using ospho on bare steel. It leaves salts behind that cause osmotic blistering. When I talked about flash rust, one guy said "oh a little rust underneath is ok."

One could not understand why I used zinc epoxy primer for an under under water application. I didn't ask him where he would use it. I didn't want to sidetrack the conversation.

One guy simply said he had no idea, the other insisted I have to sandblast the hull again and start over without the ospho.

Where I have addressed the blisters before is fine, these new blisters are in previously ok areas. I feel strongly that if it were the ospho (which I washed off with acetone) I would see some vertical pattern of some kind that indicated areas where I had not cleaned sufficiently. But there is nothing streaky, just irregular areas.

[boden36]

If you use a zinc paint under water it will act like an anode and blow the paint off.
Blisters mean contamination or maybe the paint was not dry enogh when you overcoated and the thinners have caused blistering.
I have been taught that abrasive blasting does not remove all contaminants, and that you should blast, then waterblast then lightly blast again before painting. This works well for me but is a lot of mucking around.

Regards,

Richard

[hellosailor]

Rashly assuming "ospho" means some kind of oxalic acid, like Bartender's Friend, I have no idea what that might leave behind. But if it left water-soluble salts, there's no reason to think acetone would dissolve or remove them. Acetone is a good degreaser, but not a universal solvent. So they might be on to something there, or it might be a red herring.

[a64pilot]

Ospho is Osphosphoric acid and does what Glenn says it does, converts iron oxide into iron phosphate, called rust killer by farmers and the like.
Don't know if it's the ticket for boats, but it's great for farm equiment.

[conachair]

Originally Posted by hpeer

When hauled I now have areas on the hull with small, dime size blisters.

Did the blisters have a tiny black dot in the center?
I had a similar problem on a steel boat apparently caused but too many zinc resulting anodes resulting in cathodic disbondent.. http://www.corrosionpedia.com/defini...ic-disbondment
Removal of some anodes seems to have cured the problem. Complicated down there but worth investigating.

[hpeer]

The first blisters were(some) quite large with no water in them. And they appeared before the boat was put in the water.

The zinc primer has four coats of ameron 235 rust bar on top of it then a coat of ameron ABC3 bottom paint. One would think that would keep the water off the zinc primer. No?

Damned if I know about the tiny black dot. I'll have to look.

Im pretty sure this last batch of blisters, that appeared after the boat was launched, are from osmosis, the ones I popped all had water in them. So clearly there is some kind of contamination, I guess. I just don't know the source.

The real itch here is, how do I know when I'm done with this damn mess? Did all the bad spots show up? Or am I gonna get more next summer?


I know no one knows, that was rhetorical! It rationalizes my drinking!

[AndDavRos]

Greetings all,

I have some info to add, and a few questions of my own. (not trying to hijack the thread)

We have a '95 Roberts 46 on the hard going through winter refit before we move aboard. We are stripping the paint below the waterline b/c of blisters (about 2mm in dia) that have shown up all over the hull. As best we can tell, it was byproduct of over-zinc'ing the boat, but I don't have much data to prove that.

Ameron paints are great! have used them inside (Amercoat 240) and the stuff will set up even if water gets on it while wet.

We are using angle grinders, flap disks and brush cups to remove the old paint (4 coats of two part epoxy are HELL to remove!) but due to weather and our time constraints, we can't strip the whole boat and then paint without: rain and snow storms, and temps swinging between 70F and 30F for several days between trips to the yard.

I was going to strip the whole hull and use a small dustless sand blaster to profile the metal, then treat with ospho before using Amercoat 240. Paint one side at a time? or small sections? or just leave bare metal, hit with ospho one day, paint the whole mess the next?

does anyone have anything concrete about using ospho with Ameron? this is the second time I have heard someone say it's a bad idea. Should we rinse the hull with water after using the ospho to remove any salts? will this cause rust?

What are you doing about the cold temps? do you heat the area/metal prior to painting? maybe use a heatlamp?

Good luck and thanks in advance for the input anyone can send my way!

-Shawn