Single pack anti corrosives

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saltyrob

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Hi,
There is a bit in PBO ,'Ask the Experts', on treating rust spots on keels.Reference is made to single pack anti- corrosives. Would be gratefull for some product names before I buy the wrong stuff.

Many thanks

Rob /forums/images/graemlins/confused.gif
 
I think the main difference is between the 2 pack epoxy systms which have to have pure clean 'white' metal as a base (and this means a sand blaster or similar)....
or
Single pack which claim to convert the rust from FeO2 to somthing else more inert.
or
Single pack which have a high Zinc content which presumably works a bit like galvenising.

I have used some stuff called Fertan (you can Google it). It is an organic single pack which resembles creosote.I understand it is similar in composition to the active ingredient in Oak that will prevent tools rusting when stored in Oak chippings (poss Tannic acid?). This stuff works as a converter.

Hope this helps

Nick
 
In general single pack products give a lower performance than 2 pack anticorrosives but they are more surface tolerant.
Keels are usually made from cast iron or lead. Cast iron is difficult to prepare to a high standard but dry abrasive blasting is the best by far and if you go to that expense it is worth spending money and time on a good anticorrosive.
Grinding the surface back is second best and if done well probably still worth a good paint scheme.
Wire brushing or sanding comes a very poor third in standard of preparation and it is only worth putting a basic single pack paint on. Wire brushing will get a nice shiny finish but it is actually only polished rust - which will carry on rusting!
Don't confuse rust converters with anticorrosives. They are very different animals and massively inferior. No coating company will recomment a rust converter before their products as the adhesion will be compromised.
Someone has mentioned red lead and Hammerite. Red lead is just a coloured paint suitable for underwater use. Since added lead is banned the "red lead" is just a pigment with no anticorrosive properties whatsoever. Hammerite is not designed for permanent immersion and will not last. Also some of the hammerite products are very difficult to overcoat and your antifouling will probably fall off.
 
The reference in PBO is to singlepack conventional primers as opposed to two pack primers like epoxies.

Take a look at International's website www.yachtpaint.com/uk

I have not tried Fertan, than Nick suggests, underwater. Its pretty good on rusty cars though. (Or was he suggesting creosote /forums/images/graemlins/grin.gif He ought to know what creosote is as at one time he kept a boat at a yard that practically floated in it ).

Jenolite has been mentioned. It may or may not be available but it might be worth looking at Jenoseel http://www.jenolite.com/shopping_cart_jenoseel_marine.htm which appears to be recommended for marine use.
 
I was always puzzled by Fertan and the theory that tanins could preserve steel. I am also thrown by the idea that keeping tools in oak chippings would prevent them rusting.

I say this because I had problems with steel bolts through oak floors that corroded rapidly and badly, also the oak lost its strength and went brittle around the bolt holes. I was told that this was due to the tannic acid in oak and that I should replace the bolts with copper ones which I did. I also replaced the oak with iroko, which is all I could find at the time.
 
Fertan offer this patent as an explanation of how it works.

http://www.fertan.co.uk/patent.htm

I think that explains it all clearly enough
<span style="color:white"> .................................................................... </span> /forums/images/graemlins/laugh.gif
 
More points to consider:

Cast Iron is porous, primarily because of contamination during the casting process. If you want to stop it corroding the cleaning process must offer a clean medium at all times; this means rotating tools represent a dirty or contaminated surface and only spread contamination. Dry grit blasting presents only clean abrasive material at all times.

However because of the porosity inherent in cast iron it may also contain moisture, this must be removed prior to blasting, as moisture is one of the elements required to form rust.

The objectives are simple, achieving them is not. All we need is a dry surface with good key, add any coating that will protect the fresh surface, exclude oxygen and prevent moisture penetration.

For my money I find drying the cast with heat after standing for several weeks, dry blasting, priming with zinc at the required thickness (this is critical) and within the shortest possible time because cast iron will flash rust. Then coat with an epoxy, at least 4 coats followed by a protective coat for the epoxy, preferably something that is designed to be submerged and withstand growth, like the stuff used on steel piles in harbours.

Avagoodweekend,,,,,,
 
So, priming with oxide based paints, ferrous or ferric, is no better than any other primer?

And reducton of oxides (using phosphoric acid or whatever) is no substitute for cleaning properly and then protecting?

That means there's quite a bit of snake oil on the market! As usual of course. Whenever there's a common problem . . .
 
As mentioned above "Red Lead" doesn't have any lead in it. Its not Iron Oxide in a paint medium, so you'll be painting oxide on to stop oxide? Hammerite has perhaps an undeserved reputation. Its excellent for what it does, but it isn't the indestructible do all paint that some make it out to be.

To stop corrosion (assuming you're avoiding the electrolytic methods), you need an impermeable barrier to stop the electolyte (seawater) getting to the cast iron. This means the most impervious, tough paint you can get.
Most paints are actually porous, but its a matter of how fast that permeability happens.
The best are those with flakes of mica or similar, to help prevent ingress. And those with the strongest bonding systems. The "one pack" or "two pack" terms refer to the curing mechanism. Many paints cure by absorbing moisture from the air - "single pack" systems. But some have a second substance to set off a chemical reaction. (2 pack). A bit like araldite glue, useless unless you add the hardener, but when you do, - solid!

Then there are many genereic types of paint - alkyd, polyurethane, polyester, epoxies etc.
Prob best with an epoxy (tough, better resistance to water, but not excellent uv resistance, but for a keel not such an issue)
 
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