Rust Converters?

[Amp1ng]

Why do people seemingly avoid using rust converters or paint over rust systems for treatment of steel below the waterline?

I have twin keels which at present are showing limited signs of rust bloom beneath the existing coatings. At the end of this season I intend to address the issue but I'm concerned that from what I have read on other posts one needs a lot of money, time, effort and luck during preparation of surfaces and timely application of epoxy systems within the correct tolerances of temperature and humidity and yet it could all still be in vain depending on the things like casting quality during original manufacture and or the mood of the gods on the day.

I have a pot of POR 13 in my garage which is a single part urethane based product which apparently cures best in a humid environment, is not temperature dependant and once gone off creates an impermiable barrier over existing rust thus sealing it and preventing any further oxidisation. What say anyone if I were to get the keels blasted during the winter, cleaned down and irrespective of the weather or if there were microscopic rust cells already beginning to form, put a couple of coats of POR on the keels followed by a few coats of primocon followed by an epoxy system and then antifoul?

 

[Avocet]

POR 15 is brilliant on cars, I've used it myself. Not sure how well it would do when continually immersed though. Also, in my experience it seems to stick best to slightly rusty metal anyway. No idea whether primocon would stick to it though.

 

[Sandyman]

Cant see any reason why that would not work.

We're steel and over the years I have tried many different solutions and found this product worked the best for me: http://www.fertan.co.uk/Item-Fertan rust converter.htm

I used to have two or three places on the hull which were a constant problem until I used Fertan. To problems since.

 

[rickym]

Fertan and Primocon works for me

 

[BlueChip]

I coated some rust spots on my keel last year with Loctite 7503 - 12 months later no sign of rust in those places.

 

[MoodySabre]

I use Vactan - cheap from an ebay shop. Excellent stuff.

 

[gasdave]

I used Fertan and Primacon last spring after a thorough preparation to bright metal. Boat's been in the water for a year now so I'm looking forward to rust-free keels when I have her lifted soon for a re-antifoul!

 

[KellysEye]

I've always found that rust converters last about two years max then the rust returns. Basically RC's are a bodge job, you need to remove all the rust and paint properly starting with a zinc rich epoxy. Obviously others may have different experiences.

 

[vyv_cox]

I've always found that rust converters last about two years max then the rust returns. Basically RC's are a bodge job, you need to remove all the rust and paint properly starting with a zinc rich epoxy. Obviously others may have different experiences.

I agree. Some years ago when I was still in Research some colleagues evaluated every rust converter they could lay their hands on. Sponsor was a major North Sea operator. They found that removing rust mechanically followed by primers and topcoats was more effective than any of the converters.

Standard treatment on offshore platforms is now grit blast to Sa 2.5, or needle-gun where grit cannot be used, zinc rich epoxy followed by high build epoxy middle and top coats. The much publicised Forth Bridge current treatment is very similar.

 

[Sandyman]

Can anyone point me in the right direction as to where I can find out what this stuff is that they are treating the Forth Road Bridge with. Someone last year was telling me about it when he saw we were Steel and said it was developed for underwater use in the first place. Though I don't know how true that is. No doubt it cost an arm and a leg but in the long run could be worth the investment. Thanks.

 

[Conachair]

I agree. Some years ago when I was still in Research some colleagues evaluated every rust converter they could lay their hands on. Sponsor was a major North Sea operator. They found that removing rust mechanically followed by primers and topcoats was more effective than any of the converters.

Standard treatment on offshore platforms is now grit blast to Sa 2.5, or needle-gun where grit cannot be used, zinc rich epoxy followed by high build epoxy middle and top coats. The much publicised Forth Bridge current treatment is very similar.

I think the question is does epoxy adhere better to iron oxide or iron phosphate. Assuming that shot blasting isn't an option of course.

I've prepared steel using wire brush in a grinder, flap disk in a grinder, sand paper, you name it. It will look completely clean. But on a hot day as soon as you put some ospho phosphoric acid on it then you can see all the pits bubbling away as the acid does it's stuff with the rust hidden away from the naked eye in the pits.

Very hard to be accurate without spending a few years in a university somewhere but i think it's better painting after phosphoric acid than without. Problem is it will take about 5 years with each thing you try to know if it works

But as ever preperation is everything, mechanical as clean as you can and getting the excess ospho off seems vital which ain't easy in the corner of a bilge somewhere.

Favorite holding coat primer this week is this one

I think with keels the amount of impurities in the steel might vary hugely so what works for one boat may well fail on another.

 

[Seanick]

http://www.brewersprotectivecoatings.co.uk/datasheets/technical/BRAT_EU96.pdf

 

[jonoR]

Rust Inhibitor test over 5 years

Hi all , my friend, who works with steel , sent me this site. The man painted steel sheets and left them out in all times of weather . He even put them in his swimming pool. Here is the Link . It is worth reading from start to finish , but the end results are on the last post (13) of the site
http://www.thesamba.com/vw/forum/viewtopic.php?t=131753&postdays=0&postorder=asc&start=0

 

[Conachair]

Hi all , my friend, who works with steel , sent me this site. The man painted steel sheets and left them out in all times of weather . He even put them in his swimming pool. Here is the Link . It is worth reading from start to finish , but the end results are on the last post (13) of the site
http://www.thesamba.com/vw/forum/viewtopic.php?t=131753&postdays=0&postorder=asc&start=0

Interesting. Nothing works Thanks for the link. I wonder how the panels would have fared with some 2 part epoxy ontop.

Some light reading here

 

[oldsaltoz]

Why do people seemingly avoid using rust converters or paint over rust systems for treatment of steel below the waterline?

I have twin keels which at present are showing limited signs of rust bloom beneath the existing coatings. At the end of this season I intend to address the issue but I'm concerned that from what I have read on other posts one needs a lot of money, time, effort and luck during preparation of surfaces and timely application of epoxy systems within the correct tolerances of temperature and humidity and yet it could all still be in vain depending on the things like casting quality during original manufacture and or the mood of the gods on the day.

I have a pot of POR 13 in my garage which is a single part urethane based product which apparently cures best in a humid environment, is not temperature dependant and once gone off creates an impermiable barrier over existing rust thus sealing it and preventing any further oxidisation. What say anyone if I were to get the keels blasted during the winter, cleaned down and irrespective of the weather or if there were microscopic rust cells already beginning to form, put a couple of coats of POR on the keels followed by a few coats of primocon followed by an epoxy system and then antifoul?

It should cure well as it needs moisture to cure. I suspect the main problem with most cast iron keels is in fact the moisture content when treated with zinc and epoxy combinations.