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Old 10-09-2014, 00:48   #1
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Rust bubbles, penetrating epoxy, and acid etching of steel hull

Hi all,

We are new (proud?) owners of a live aboard steel yacht in Tromsø, Norway, which in terms of service and available materials is some kind of end of the world. Plenty of boats, yes, but almost all fiberglass, so no experienced fishermen to ask for tricks and workarounds on steel. We obviously have lots of questions regarding maintenance of the steel structure with more or less alternative methods, and are quite unsure about many things. Maybe you can help? ANY advice highly appreciated, although we will keep our brains switched on.

In Scott Fratchers DIY guide for metal boats and in another magazine article I read about so called penetrating epoxy to be used as the first layer right after preparing the steel. I think they refer to it as pre-primer, and both sources recommend the Ameron brand. Unfortunately, we could neither find Ameron, nor any other product marked as penetrating epoxy here in Norway. After some thought and reading the mighty internet, I understand that the idea of such a product is to completely seal off remaining rust (see next question), such that it stays anoxic and stops developing. Obviously, nothing will penetrate steel as such, but is the idea maybe to start off with an especially fluid/ thin layer of epoxy to flow into the pits and crevasses formed by rust to displace the air in there? If so, can't we just take any cheap epoxy primer and thin it out with whatever thinner fits for that system and use that as our "penetrating epoxy"?

The next mentioned and disputed topic in the two sources mentioned above is acid etching, where you treat your steel surface with phosphoric acid which reacts with remaining rust in pits and renders it inert. We couldn't find pure phosphoric acid, but rust remover products with phosphoric acid as active ingredients, which I assume are thinned out acid. These products are thick and milky in appearance. I understand that physically removing all rust is the best way to go (sand blasting, needle gun, whatever), but that is not possible everywhere, e.g. under the prop shaft, where physical space for power tools other than Dremel type tools is not given. The product we used made the remaining rust black, and (after thorough washing) left the blank steel appear golden. What are your experiences with acid etching, and do you think a rust remover product is an acceptable alternative to pure acid?

Another more general question I have is what kind of rust is to be treated? We do have anti-slip mats glued to the deck which we wish to remove some time in the future suspecting ugly rust patches under them and creating a bigger job, but for now I'm thinking about regular routine on the go. Obviously, pit-creating rust bubbles should be treated, and I heard from other steel boat owners I talked to earlier that that's not too much of a deal when having the right routines and space, especially when living aboard (It's very cold and moist here, which might give us some headaches, but that's another topic). However, what about surface rust? I'm talking about that thin layer of rust often seen on building machines such as snow plow blades etc. A polish boat builder I talked to said that we should not touch it unless bubbles appear. Any opinion about that?

Last I would like to mention that from our understanding, sand blasting is not banned here (yet?). Do you think getting a compressor mainly for small scale fixing of rust bubbles etc is worth it? And is that an easy job, i.e. can we mess up the whole thing and blow away steel or something? Is the area ready to "pre-prime" or whatever the second we are done with blasting? Or are we fine with a angle grinder fitted with a steel brush and some thinned acid product, and leave the sand blasting to a professional when we have the whole deck to do?

Long thread, but maybe some interesting discussions coming out!


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Old 10-09-2014, 01:37   #2
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Re: Rust bubbles, penetrating epoxy, and acid etching of steel hull

I would consider rust convertors a temporary solution only.
If you can buy a suitable compressor that has the capacity to run air tools, get a needle gun to clean most of the rust, and then abrasive blast using a proper media like garnet. Do not use sand, the dust can kill you.
I use a little hand held blaster that has a hose that sucks the grit out of a bucket and it was very cheap to buy.


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Old 10-09-2014, 01:54   #3
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Re: Rust bubbles, penetrating epoxy, and acid etching of steel hull

A few thoughts:-

I have no idea where penetrating epoxy could be found. I'm aware of a product that can be used to seal concrete but not steel. I've used POR 15 with some success but I understand it to be a solvent free polyurethane.

To the best of my knowledge phosphoric acid does not actually etch steel. It converts iron oxide (rust) to iron phosphate.

The fundamental problem with treating rust is to prevent rust particles from being covered in paint. Rust on a boat seems to have the unique property of retaining water or even salt water. If this rust is covered by paint the water "enables" oxygen to attack the steel, the resultant rust lifts the paint and we have a rusty boat.

Using phosphoric acid seems to slow this process but does not prevent it.

My experience has been that physically removing the rust while abrading the steel is the best possible preparation for painting. Abrasive blasting is by far the best, but on smaller jobs I have used a light die grinder type tool with a diamond bit (ebay!) followed by the POR 15 "etch" primer, followed by POR 15 enamel, followed by an enamel top coat before the POR 15 is fully dry to fair effect.

My recollection is that Ameron has a similar coating.
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Old 10-09-2014, 03:15   #4
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Re: Rust bubbles, penetrating epoxy, and acid etching of steel hull

you might look into hot zinc spray galvanizing,ideal for use in cold damp conditions like you have

What is Zinc Spray Galvanizing? - Definition from Corrosionpedia
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Old 10-09-2014, 04:15   #5
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Re: Rust bubbles, penetrating epoxy, and acid etching of steel hull

Greetings and welcome aboard the CF, Phil.
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Old 10-09-2014, 04:36   #6
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Re: Rust bubbles, penetrating epoxy, and acid etching of steel hull

If the rust is extensive and if it is permanently underwater or close to the waterline (I guess everything is, in Tromso) then you may be tempted to strip the whole bottom then either zinc it and epoxy it, or else epoxy it. I think stripping is best done by sanding and you are unlikely to go with the project in Tromso unless you go into a shed. The stripped hull must be overcoated immediately and moisture will make applying epoxy coats tricky.

Smaller gaps can be locally blasted or grinded and epoxied. This is good technique in between major overhauls.

You will find plenty of advice on the web as to how to treat a steel hull. Pick one that fits your levels of love for maintenance / your love for sailing.

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Old 10-09-2014, 07:00   #7
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Re: Rust bubbles, penetrating epoxy, and acid etching of steel hull

We have a steel boat and we love it! All things considered I think steel is low maintenance.

The exterior of our boat was spray galvanized when she was built in 1981 and I have no doubt that it has helped with corrosion immensely. Areas that have been repaired or replaced over the years that are not galvanized do not hold up quite as well.

Our boat is not painted with anything fancy... above the waterline and inside we use Rust-Oleum purchased from the hardware store. This product is an exterior oil based alkaloid enamel. Under this we use Rust-Oleum rusty metal primer. Rust-Oleum is inexpensive and can be purchased anywhere here in the states. We do have to do some touch-up, but much of it can be done underway with a disposable brush. Bernard Moitessier recommended six coats of enamel in his book The Long Way. We use two coats, but we are in the Great Lakes which is fresh water. However, our boat spent half its life in salt water and has been painted with Rust-Oleum since new. I do believe the new epoxy paints would be superior in durability to the Rush-Oleum. Below the waterline we use Pettit Unepoxy and have been happy with it.

Some areas of our boat were painted at one time with polyurethane paint that did not hold up. It was a mess and I had to scrape it all off. I know people say the new polyurethanes are amazing... but I would stick with a good enamel or epoxy on a steel boat.

We like using a carbide hand scraper to remove old paint and rust. It is VERY fast and produces more chips than dust. These scrapers have replaceable carbide blades that are cheap. Don't bother with steel scrapers... they just don't hold up. Buy carbide and you can scrape all day and it is still sharp. Follow the link below to see a picture of the scraper we use. You can also flip the blade around in the scraper and scrape pushing away to get into some areas. We also do some scraping of tight spots with screwdrivers. Don't use cheap screwdrivers... buy the best you can get with hard steel. And get big ones so you have a nice big handle. You can buy a couple and bend them to get into your tight spots. Throw them in with your painting supplies and use them for many years. Sharpen them flat and square again with a file when they get dull. You will be surprised how fast and effective scraping is compared to other methods on steel.

I do not know of any penetrating epoxy but we have used regular thickness epoxies with good success. Even though they are fairly thick in appearance, they take a while to cure and that time allows them to flow readily and achieve good wetting of porous material such as rust. Any time you thin epoxy you increase the risk of decreasing it's physical strength so we have not done it.

Sandblasting it trickier than you think. First off the dust from sandblasting is really dangerous to inhale! If you inhale the tiny silica sand particles they never leave your lungs and give you a condition called silicosis that worsens over time. A regular dust mask is completely ineffective for sandblasting... you need a completely sealed respirator. Secondly, sand blasting requires enormous amounts of air. Even the small portable sandblasting units require lots of air... a pancake style compressor will not do it.

Remember that one of the virtues of an older steel boat is usability. Don't get hooked on trying to shine her up like a new penny... see the beauty in her patina of age and experience. If you try to have a deck that is smooth as glass you will drive yourself nuts. Just get her scraped and painted and she will look sharp! People will admire her for her strength seaworthiness. When she gets dinged and chipped just pry open a quart of paint and slap on a few coats to touch her up with a disposable brush. This way you both can spend more time sailing and drinking beer!

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Old 10-09-2014, 07:56   #8
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Re: Rust bubbles, penetrating epoxy, and acid etching of steel hull

There are a number of penetrating epoxies sold, generally marketed for restoring rotted wood. I've used CPES myself.

CPES Warm Clear Penetrating Epoxy Sealer

TotalBoat Penetrating Epoxy
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Old 10-09-2014, 08:17   #9
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Re: Rust bubbles, penetrating epoxy, and acid etching of steel hull

Grit blast steel then epoxy coat. Penetrating epoxy is for porous material like plywood or foam filled cores or to fill voids.

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Old 10-09-2014, 09:32   #10
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Re: Rust bubbles, penetrating epoxy, and acid etching of steel hull

Phil, how much area are you planning on refinishing? If you are doing the whole hull, you need major sand blasting equipment, and the hot zinc spray is costly, but works very well. If you are doing small touch up, a medium size compressor, and a cheep siphon type sandblaster will work fine. I just did some blasting yesterday (not a boat) and my old 2 HP compressor, and a 50lb pot of grit got a lot done. I had to wait sometimes for the pressure to build up, but I needed the breaks to get out from under the very hot hood. As has been stated, dont use sand. There are many grits, and a supplier could tell you what is best for the type, and size of your equipment. Keeping the dust and grit from getting on other boats is why most boat yards dont allow blasting. Good Luck with it. ______Grant
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Old 10-09-2014, 09:48   #11
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Ameron sealer is the paint , fantastic stuff but takes a long time to go off. If you can sandblast then not such a big deal, but when you ll can't this is the best I've come across after many years living aboard a steel boat.
Might be rebranded now as ppg
Edit, looks like ppg distribute it now, might be worth an email to ask about stock in Norway, or the UK company will probably ship it, I've used them before and they seemed helpful.
Good luck.
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Old 10-09-2014, 09:49   #12
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Re: Rust bubbles, penetrating epoxy, and acid etching of steel hull

West (think) says the first coat of epoxy can be worked in with sand paper or a wire brush after the steel is preped to help with bonding.

I went with Amercoat 240 , a PPG product, on blasted steel. Its almost impossible to remove. I did this inside and out.
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Old 10-09-2014, 11:02   #13
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Re: Rust bubbles, penetrating epoxy, and acid etching of steel hull

Welcome to the world of steel boats.

Forget about sandblasting inside the boat, unless its a total strip out.
One of my favourite tools is a battery drill on slow speed with a flexible "Pferd" type of 1mm cutting disc. Slow grind, you don't want the sparks to fly to anywhere they can start problems.

On general large areas an epoxy system must be used. We like the Sigma Kalon Products, a Dutch company, but there are other brands in the EU like Jotun, Hempel etc. The Sigmacover primer 7413 is an Aluminium based High Solids epoxy. This mus be thinned to 30% for the first coat, and the second is applied 5% thinned. After that 2 x Sigma BREA an epoxy tar, then Sigma TCN Tiecoat. These are all two component paints. It is a system. It s very important to apply the first coat of 7413 within minutes of preparing the naked steel. This is for LARGE areas.

Lets talk about small repairs. Here, I diverge from the epoxy methods, and go back to alkyd or oil based products. What happens if you cannot prepare the substrate 100% perfect, and there is still a cell or pit of rust, is that overcoating with a hard inflexible epoxy system will fail. This is because the small pit will slowly expand and then it lifts the epoxy paint around it. Because the epoxy is strong, and inflexible, it lifts an area bigger than itself, creating a bubble, and then the rust grows in that "covered" place. The chemical reactions are different in the anaerobic space, but sometimes more destructive. So in these places I use the dremel, or grinding, filing, picking whatever I can to remove the 95%. To convert with acid is next. In Spain you can buy a product called Ferronet, witch does a good job, but the best product is Oshpo. I put it on with an old toothbrush, and massage in for about 15 minutes. Then remove the excess (dirty) acid with a dry cloth. Leave it for 24 hours in a dry condition. Next day there should be a grey powdery substance, and the remaining red rust must be black, hard, and scaly, but you are unable to pick off, if you can pick off, you did not go far enough yesterday.

Next is to wire brush the loose stuff away and apply a Zinc rich primer, this can be a Zinc Chromate, or something like Galv-o-coat from Hempel. Most important is that a litre of whatever you buy must weigh 1.6 Kilos or more!!!! So it has a high metallic content. One coat only!

Next is an old fashioned Red Lead type of paint. In Spain the company Titan makes one called Mineo de Plomo. It is bright orange. Also HEAVY. You need two coats. Next is a build coat, this can be a one part thixotropic gel polyurethane, then you can start fairing, and topcoating. When you fair it. Make some pencil lines around the job. Paint over them, and as you build and sand, build and sand, you stop when you see the pencil line, and do not sand the pencil line away, as that was the proper level.

The reason for this method, is that now, as in the epoxy case above, IF the job fails, and the rust pit starts growing, it will pop out right where it is, leaving the surrounding paint intact for many years, the oily nature of the paints used are too weak to lift surrounding good paint, causing "bubbles"

We spend about 30 Man-hours a year on rust prevention/correction and it is a small price to pay for the security and strength of a steel hull.

Be Very careful of Stainless steel in close proximity (<20mm) to the steel hull, in an electrolyte. Eg. If you have a stainless steel strumbox on a pump suction, and it is submerged in bilgewater, the stainless will drill a hole electrically through the closest steel no matter how well it is painted.

DO put anodes in your bilges, in your holding tank.

Good luck...
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Old 10-09-2014, 11:37   #14
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Re: Rust bubbles, penetrating epoxy, and acid etching of steel hull

A lot of stripping paint from steel has to do with the condition of the paint. If the paint has a poor bond you can remove a large amount of it in a surprisingly short period of time, if it is a hard finish type of paint (such as a 2 part) and it has a good bite on the steel it can be pretty slow.

My favorite tool for reemoving paint from flat steel surfaces is a "angle" or "side" grinder with a wire "cup brush"

There are 2 main sizes of these grinders, 4 1/2" and 7". They look like these:

A cup brush looks like this:

For precautions, wear one of those clear plastic face shields as the little wires do fly off so just safety glasses don't protect enough. Also wear leather work gloves.

About the only thing to be careful of is pushing too hard, sometimes the wires will put a swirl in the metal which will need filling with a glazing compound to alleviate. So just keep enough pressure to keep the paint coming off and you'll move along pretty good.

In regards to air tools, I had a 22' sailboat that I sanded the hull with a air powered double action sander and it took me 2+ days to do, and that was with an air compressor with a 20 hp electric motor! If you decide to use air tools, I would say a 6.5 hp motor is bare minimum and 8-10 hp is better.
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Old 10-09-2014, 13:41   #15
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Re: Rust bubbles, penetrating epoxy, and acid etching of steel hull

Here is my recent experience, good or bad.

We have two steel boats both early 1980's vintage. The big boat was coated with aluminum at time of construction. That seems to be holding up well.

The small boat was developing tiny blisters on the hull, even while sitting on the hard. I mean tiny, smaller than a small pea, #2 bird shot. It was more on some plates than on others. I had her sand blasted, took two days.

Day 1 am they sandblasted the port side. Under a poly tarp. I then washed the hull with acid, then washed with acetone, then put on a coat of Ameron zinc epoxy primer.

Day 2 repeat on starboard side. Then I put a second coat on the entire hull.

About two weeks later blisters, some blisters appeared on about 1/3 of the hull. The blistering was on all plates but only in localized areas of the plates. I could not find any pattern to it what so ever. I talked to two experts at Ameron. In short they had no convincing story of why I had blisters. The blisters were dry and if I cut them out you could see where the paint had stuck to the hull, but it had separated. The Ameron experts were surprised that I used the zinc primer for an underwater application. Damned if I know where you would use it if not underwater. Anyway their theory was that I was getting osmotic blistering from salts left over after washing the hull with acetone. The one guy said "Aw, some rust blush never really hurt." I could not figure out how you get osmotic blistering if the boat is on the hard and dry. Oh well. Clearly the experts were more along the lines of tanker and oil platform men, the idea of a small steel yacht was a bit of a wonder.

I sanded out the blisters and repainted the effected area. That was largely effective, but I still had some blisters, so I did it again. The bottom looked pretty good after sitting some time so I put on the first coat of Ameron 235 Rustbar. With the slicker finish I found a (very) few more blisters, which I cut out with a knife and repainted. That seemed to be the end of it.

I have now applied: 2 coats of Ameron zinc epoxy and 4 coats of Ameron 235 Rustbar. The boat was on the hard for a few months and there has been no sign of any recurrent blistering. Go figure.

The sand blasting did revel a couple of small areas where I needed to do hull repair. I'm not sure sanding or other techniques alone would have exposed this weakness. I took care of those areas obviously. The hull was just given an audio gauge and came out fine. No problems found.

That being said, I would not trust an audio gauge. During the refit I found a small "pimple" on the top of the coach roof, inside a dorade. Picking at the pimple I found it went through the roof, when I cleaned it up with a dremel it was a hole about the size of a dime, perfectly round. I welded it up. The whole operation took maybe two hours, mostly because I had the welder right there.

But that has been my experience, you can get some kind of "defect" or a persistent water drip that can cause VERY localized rust that would only be found with audio gauge by dumb luck. The two best tools for finding rust are the Mark I eyeball and a ball peen hammer.

My experience with the Ameron is that if you do a sufficient prep job the stuff does its part and sticks real well.

I agree with most of what MBWhite says above. If I had to do it over again (NEVER AGAIN) I would be tempted to save the $$$ and attack the hull with a grinder using a flap wheel and cup brush. NEVER use a grinder without sturdy leather gloves, I use welders gloves. It's interesting to see wee puffs of masticated leather fly off and realize that if not for the glove that would be your finger. Grinders require a dust mask (minimum) and for the epoxy you need the appropriate mask with organic canisters. You might be able to buy them from your paint supplier. In the US Ameron is sold by PPG (Pittsburgh Plate Glass.)

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