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Thread: Has anyone used POR-15 on a rusting iron keel?

  1. #1
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    Default Has anyone used POR-15 on a rusting iron keel?

    The cast iron keel of my boat has sprouted a fair amount of rust break-through... it's a 2005 Jeanneau, which is built with an iron keel that was covered with gelcoat at the factory. Over the years, as one would expect, the gelcoat has crazed and cracked, permitting rust to break through the coating. In previous years, I've sanded it and covered it with bottom paint, but this year, the rust has really taken over, so I'm going to have the keel soda-blasted down to bare bright metal, and plan to immediately apply a zinc phosphate coating, followed by two coats of POR-15, a rust-preventative paint, to be used as an undercoat for my regular bottom paint.

    I was wondering if anyone had experience with POR-15, and could offer any tips?
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  2. #2
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    Default Re: Has anyone used POR-15 on a rusting iron keel?

    I've used it on my cast iron heat exchangers. I just chipped the loose rust and applied. Held engine enamel well enough. I dunno about antifoul.
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    Default Re: Has anyone used POR-15 on a rusting iron keel?

    I've used it on several trailers with no issues at all. I don't recommend getting it anywhere you don't want it though. It has to wear off of your skin.
    The best helping hand you will ever receive is the one at the end of your own arm.

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    Default Re: Has anyone used POR-15 on a rusting iron keel?

    Anything with a name like POR-15 has to be overpriced...I cleaned a rusty iron keel with sanding discs and a wire wheel and hit it with two heavy coats of Rustolem Rusty Metal Primer. Waited a week and painted it with Petit Hard Ablative anti foul and it worked a charm. Rustoleum is cheap and readily available.....just my two cents worth...

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    Default Re: Has anyone used POR-15 on a rusting iron keel?

    Quote Originally Posted by willin woodworks View Post
    Anything with a name like POR-15 has to be overpriced...I cleaned a rusty iron keel with sanding discs and a wire wheel and hit it with two heavy coats of Rustolem Rusty Metal Primer. Waited a week and painted it with Petit Hard Ablative anti foul and it worked a charm. Rustoleum is cheap and readily available.....just my two cents worth...
    It's really not that pricy, and it cures with moisture. Harder than Rustoleum too. I like and use Rustoleum, just sayin.
    Ratus ratus bilgeous snipeous!

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    Default Re: Has anyone used POR-15 on a rusting iron keel?

    Its single pot . I've used it it on cars and for the boat gearbox etc but I would be looking into a two pot system for a job like that.

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    Default Re: Has anyone used POR-15 on a rusting iron keel?

    I've used it on several things, including a boat trailer, and an outdoor table. Quite pleased with the results, but the smell bothers me the way very few solvents do.
    David G
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    Default Re: Has anyone used POR-15 on a rusting iron keel?

    I went the hard way: hit with air hammer until shiny (the keel - definitely not me!) & then coat in epoxy. I mean air hammer - a needler wouldn't touch it. I did it in roughly 2'x2' patches - based mostly on how long I could stand the vibration, tyvek suit, mask, ear defenders & face shield. The bottom of the ballast was particularly fun. I'll need to do a couple of small sections after the next boat move because the blocking covered some.

    We'll see how it stands up.
    "If it ain't broke, you're not trying." - Red Green

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    Default Re: Has anyone used POR-15 on a rusting iron keel?

    I used that approach on my Tanzer 22's iron keel (boat is long since sold). From what I read in preparation, it was extremely important to seal the keel as soon as possible after blasting, sanding or whatever technique you use to get to bright metal. For that reason I had the first coat of primer on it within an hour of sanding it down. Kept the boat 3 or 4 years after that sealing, and the POR 15 did the job for me.

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    Default Re: Has anyone used POR-15 on a rusting iron keel?

    DO NOT USE POR on smooth, fresh metal. It needs a tooth to adhere such as rust or sandblasting. It will come off in sheets otherwise. Clean cast iron is still too smooth even.

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    Default Re: Has anyone used POR-15 on a rusting iron keel?

    Quote Originally Posted by ShoestringMariner View Post
    DO NOT USE POR on smooth, fresh metal. It needs a tooth to adhere such as rust or sandblasting. It will come off in sheets otherwise. Clean cast iron is still too smooth even.

    Yep. I've had both good and bad results with it. Don't really know why some worked, some didn't....
    "Travel is fatal to prejudice, bigotry and narrow-mindedness, and many of our people need it sorely on these accounts. Broad, wholesome and charitable views of men and things cannot be acquired by vegetating in one little corner of the earth all one's lifetime" Mark Twain... so... Carpe the living sh!t out of the Diem

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    Default Re: Has anyone used POR-15 on a rusting iron keel?

    Quote Originally Posted by jeaustinsail View Post
    I used that approach on my Tanzer 22's iron keel (boat is long since sold). From what I read in preparation, it was extremely important to seal the keel as soon as possible after blasting, sanding or whatever technique you use to get to bright metal. For that reason I had the first coat of primer on it within an hour of sanding it down. Kept the boat 3 or 4 years after that sealing, and the POR 15 did the job for me.
    The outfit that does the soda-blasting tells me that they will be able to bring the keel down completely to bare, bright metal. There's no way that I could do the same with sander, grinder, or any other tool... for one thing, my bad back would give out long before the job is done. This soda-blasting is expensive... but if the entire project works, it will solve the problem for longer than I'm likely to own the boat.

    My intention, with the assistance of the contractor, is to get the zinc phosphate converter onto the bright metal within an hour of soda-blasting. According to the POR folks, that will do the trick. I then have to wait until the keel is completely dry before coating with POR-15, using two coats... the second applied in about an hour, after the surface is barely tacky. Total cost for the zinc phosphate converter and POR-15 was $138.

    After that, I'll apply my usual bottom paint: Pettit Hydrocoat, the best damn bottom pain I've ever used. It's half the price of a solvent paint, and after a season's worth of use and a quick power wash, it looks virtually as good as the day I applied it. With no solvent smell, and easy water wash-up, it's a no-brainer.
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  13. #13
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    Default Re: Has anyone used POR-15 on a rusting iron keel?

    You need to watch for condensation too. If the keel is cold, and the air is warm and moist, there will be a film of water on it seconds after the media-blasting stops.

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    Default Re: Has anyone used POR-15 on a rusting iron keel?

    Quote Originally Posted by Dave Hadfield View Post
    You need to watch for condensation too. If the keel is cold, and the air is warm and moist, there will be a film of water on it seconds after the media-blasting stops.
    That's certainly true, but there's not much I can do about that... supposedly, the zinc phosphate converter is the thing to ameliorate that problem. I do have an agreement with the contractor, to insure that the whole thing is scheduled so that I can be there, with the requisite products, as soon as he's finished the job.

    Moist air, by the way, is actually an advantage, since POR-15 is a moisture-cured product. If it's very dry, it might take a long time for the first coat to 'tack up' sufficient to apply the second coat.
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  15. #15
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    Default Re: Has anyone used POR-15 on a rusting iron keel?

    Quote Originally Posted by Norman Bernstein View Post
    The outfit that does the soda-blasting tells me that they will be able to bring the keel down completely to bare, bright metal. There's no way that I could do the same with sander, grinder, or any other tool... for one thing, my bad back would give out long before the job is done. This soda-blasting is expensive... but if the entire project works, it will solve the problem for longer than I'm likely to own the boat.

    My intention, with the assistance of the contractor, is to get the zinc phosphate converter onto the bright metal within an hour of soda-blasting. According to the POR folks, that will do the trick. I then have to wait until the keel is completely dry before coating with POR-15, using two coats... the second applied in about an hour, after the surface is barely tacky. Total cost for the zinc phosphate converter and POR-15 was $138.

    After that, I'll apply my usual bottom paint: Pettit Hydrocoat, the best damn bottom pain I've ever used. It's half the price of a solvent paint, and after a season's worth of use and a quick power wash, it looks virtually as good as the day I applied it. With no solvent smell, and easy water wash-up, it's a no-brainer.

    I'd add a simple step Norm. After the POR-15 (converter), then slather a good thick coat of Coal Tar Epoxy.... Then the bottom paint. The protective skin left by POR-15 performs well in the environment it was devised for (car fenders!). The coating is very thin. The Coal Tar Epoxy will give you a bit of a shock absorber between any contact on the bottom paint and the underlying metal.

    This combo worked great on my iron keel in all the spots I was able to get down to bare metal and bottom paint (red vinyl) sticks REALLY well to the epoxy.
    Last edited by BrianM; 04-20-2017 at 12:36 PM.

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    Default Re: Has anyone used POR-15 on a rusting iron keel?

    Quote Originally Posted by BrianM View Post
    I'd add a simple step Norm. After the POR-15 (converter), then slather a good thick coat of Coal Tar Epoxy.... Then the bottom paint. The protective skin left by POR-15 performs well in the environment it was devised for (car fenders!). The coating is very thin. The Coal Tar Epoxy will give you a bit of a shock absorber between any contact on the bottom paint and the underlying metal.

    This combo worked great on my iron keel in all the spots I was able to get down to bare metal and bottom paint (red vinyl) sticks REALLY well to the epoxy.
    I did look into this. The manufacturers of coal tar epoxy recommend application on bare steel or iron... which is what the zinc phosphate converter, followed by the POR-15, is supposed to do, in my approach. From my reading, it does appear that coal tar epoxy would be an alternative to the zinc phosphate/POR-15 combination, not in addition to it. I plan to apply two coats of POR-15, which, taken together, should give me a film thickness not far from the lower end of the recommended range for coal tar epoxy, so I'm not concerned about how thin the result would be.

    While I don't doubt your testimonial to its effectiveness, I don't think I'll go that route. I'd be somewhat concerned that my preferred bottom paint (Pettit Hydrocoat) might not adhere well to it.
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  17. #17
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    Default Re: Has anyone used POR-15 on a rusting iron keel?

    Have a quick look at Vactan. Used this on several projects. The North Sea oil boys use it by the drum load.

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    Default Re: Has anyone used POR-15 on a rusting iron keel?

    Follow-up to this thread:

    The soda blasting was done yesterday... but not fully successful. The fellow who does this work discovered that the existing encapsulation of the keel.... at least, in the parts that hadn't actually cracked and fallen off... was VERY tough.... too tough even for his 375 CFM towed diesel compressor. As a result, the keel was not completely cleaned down to bare metal.

    Thankfully, he agreed to adjust his price downward... but it's left me with the task of having to fair the parts of the keep that did get down to bare metal. I applied a zinc phosphate /phosphoric acid treatment to the entire keel, which hopefully will suppress and rusting until I've had a chance to do the fairing, followed by an application of POR-15, and then, bottom paint.

    "Fact is that which enough people believe. Truth is determined by how fervently they believe it."
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  19. #19
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    Default Re: Has anyone used POR-15 on a rusting iron keel?

    My understanding is that it is a rust encapsulator & inhibiter, so I don't know how well it works on bare metal. What does the manufacturer say?

    I used it on my old Fiat Spider 2000 LE; worked like a charm.
    Gerard>
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    Default Re: Has anyone used POR-15 on a rusting iron keel?

    Quote Originally Posted by Gerarddm View Post
    My understanding is that it is a rust encapsulator & inhibiter, so I don't know how well it works on bare metal. What does the manufacturer say?

    I used it on my old Fiat Spider 2000 LE; worked like a charm.
    The manufacturer says:

    POR-15 Rust Preventive Coating is a high performance coating designed for application directly on rusted or seasoned metal surfaces and will stop rust permanently. POR-15 Rust Preventive Coating is non-porous and seals and protects many surfaces from water, chemicals, salt, and other corrosive contaminants and is able to be painted over rust. POR-15 Rust Preventive Coating is an effective anti-corrosive and rust preventive coating that offers superior chemical resistance due to its dense, cross-linked molecular composition and non-porous attributes.
    Since the photo was taken, I've started fairing the keel... not the entire thing, but the spots where the soda blaster got down to bare metal, and any other spots which were uneven. I'm using the usual polyester fairing compound... it's take a pint of the stuff so far, and I bought another pint for a second finish coat. After that, I'll paint it with POR-15... and hope that I don't get breakthrough rust again, after the season is over... it's the best I can do.
    "Fact is that which enough people believe. Truth is determined by how fervently they believe it."
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  21. #21
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    Default Re: Has anyone used POR-15 on a rusting iron keel?

    it is a simple mcu - moisture cured urethane filled with aluminum - one of many such products and probably not the best (few use 100% urethane resins and that makes all the difference) - google mcu coatings. I deal with these coatings almost every day for the past 15 years or so

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