Treating and protecting rusty keels

VicS said:
Very probably if the OP could immerse his keels in phosphoric acid until all rust etc was removed and then just leave on the garden wall they would remain rust free , just like your spanner.

Unfortunately immersing the keels in phosphoric acid may be more difficult than immersing a spanner, and he will then be wanting to withstand immersion in seawater 24/7 rather than adorning the garden wall.

It really is not a valid comparison.
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Perhaps I should have saved myself some grief and posted as Sailorman did in post #2, but here is a year old thread about rust, VicS posted in it.

http://www.ybw.com/forums/showthread.php?409987-Good-result-on-rust-with-phosphoric-acid-75

To VicS, pretty sure I wrote use a paint brush to apply the acid and didn't mention "immersion".

"Adorning a garden wall"? Hmm. Sounds a little sarcastic when leaving it on a garden wall for a year in all weathers (minus salt) has been a simple knowledge gaining expt. during which no rust has formed on treated part. I thought you were Vic the chemist who used to have the signature "chemists don't retire, they simply fail to react" or suchlike.

But if you want to be like that then:
Acid mixed with wallpaper paste works well on vertical surfaces; compares very well to the spanner expt even if you write otherwise. I have a video showing the club's steel barge used for laying moorings that I treated, but I am not going to convince anyone, so carry on, nothing to see here.

To the OP; just trying to help - I have nothing to gain here. If you buy 100ml from Ebay and try it, what have you got to loose. The acid will be of use to lawn mowers, car subframes, anything rusty.

If it works, you have saved A LOT of labour; simply wash sticky residue off after 2 weeks with water (no need to worry about a humid day) use a decent coating on top and should be good for life. I wouldn't worry about pitting (I would worry about taking good metal off my keels). Pitting can be filled with the epoxy zinc stuff, but pitting is good for hydrodynamics.

Someone will argue with that next.
 
>Didn't try them all though, so no reason to be adamant.

I had every reason to be adament, all rust converters use the same chemicals: Rust Converter, a water-based primer, contains two active ingredients: Tannic acid and an organic polymer. The first ingredient, tannic acid, reacts with iron oxide (rust) and chemically converts it to iron tannate, a dark-colored stable material. That's why there was no differences in the ones I tried, the rust came back. I only later looked up the chemicals and realised they were the same so I was wasting my time.
 
KellysEye said:
>Didn't try them all though, so no reason to be adamant.

I had every reason to be adament, all rust converters use the same chemicals: Rust Converter, a water-based primer, contains two active ingredients: Tannic acid and an organic polymer. The first ingredient, tannic acid, reacts with iron oxide (rust) and chemically converts it to iron tannate, a dark-colored stable material. That's why there was no differences in the ones I tried, the rust came back. I only later looked up the chemicals and realised they were the same so I was wasting my time.
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But the arguments above are actually about using phosphoric acid rather than a tannic acid based rust converter.
 
The KBS coatings I mentioned previously use a phosphoric acid treatment prior to painting, and my experience of how it works lines up with the comments from "Sailingsaves". After cleaning up the surface with an angle grinder, and de-greasing, the surface is kept wetted with the phosphoric acid by brush or spray for sufficient time. it is then flushed and dried before painting. Seems to work quite well.
 
>But the arguments above are actually about using phosphoric acid rather than a tannic acid based rust converter.

As I said if you use any acid you have to wash it off which is the last thing you want to do on bare metal, which will flash rust in high humidity. I can't see the problem that people here seem have about using a grinder to get bare metal and two coats of Zinc rich epoxy primer. It's simple, it works and rust doesn't come back, if any other method is used rust will eventually come back.
 
ghostlymoron said:
I think that the problem with using an angle grinder is that you have to remove a significant amount of metal to reach the bottom of any pitting.
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Not just that, but even with what looks like clean metal there will still be rust hidden in invisible pits. My experience anyway, watching apparently clean steel pop and fizz after applying phosphoric acid. In a hot country.
 
ghostlymoron said:
I think that the problem with using an angle grinder is that you have to remove a significant amount of metal to reach the bottom of any pitting.
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Cast iron has a construction not unlike a steel sponge, with graphite or nothing in the voids. A wire brush will never reach the bottom of pits, it will simply extrude metal over them, trapping rust inside. A needle gun does the same thing on cast iron but is excellent on steel.
 
KellysEye said:
>But the arguments above are actually about using phosphoric acid rather than a tannic acid based rust converter.

As I said if you use any acid you have to wash it off which is the last thing you want to do on bare metal, which will flash rust in high humidity. I can't see the problem that people here seem have about using a grinder to get bare metal and two coats of Zinc rich epoxy primer. It's simple, it works and rust doesn't come back, if any other method is used rust will eventually come back.
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ghostlymoron said:
I think that the problem with using an angle grinder is that you have to remove a significant amount of metal to reach the bottom of any pitting.
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GHA said:
Not just that, but even with what looks like clean metal there will still be rust hidden in invisible pits. My experience anyway, watching apparently clean steel pop and fizz after applying phosphoric acid. In a hot country.
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Two issues. First, there are two different materials being discussed here. Some keels are made from mild steel; others from cast iron. What is true of one might not be true of the other. I'd certainly agree that for cast iron the only way of being sure you've removed all existing corrosion is by blasting; the inclusions in cast iron mean that even material that appears to be sound might not be. When the contractor blasted my keel, it was a revelation; on one side of the keel, there was a lot of porosity and inclusions, and the blasting removed more than any manual operator of a grinder would have! I am quite sure that an angle grinder or any other surface abrasion simply wouldn't have got a good enough result. Mild steel, having far less in the way of inclusions and being a more uniform material might well be fine with a grinder or similar - provided you made sure you reached the bottom of all the existing pitting. I don't understand the concerns about removing sound material - these are keels, and anything we remove will be a tiny proportion of the whole. Fair enough on hull plating, but on a keel I don't see the problem. Removing a pound or two of metal from something weighing in the region of a ton isn't significant!

I have no experience of the acid treatments, but would expect them to be ineffective on cast iron, again because of existing porosity and inclusions.
 
>I think that the problem with using an angle grinder is that you have to remove a significant amount of metal to reach the bottom of any pitting.

That's true but if you don't flatten the pits then there will be rust in them which means the grinding has been a waste of effort. Pitting usually only occurs if rust hasn't been treated quickly, which is a must do.
 
That was my point. If you've got to remove 5mm, that's quite significant and may just expose more defects.
KellysEye said:
>I think that the problem with using an angle grinder is that you have to remove a significant amount of metal to reach the bottom of any pitting.

That's true but if you don't flatten the pits then there will be rust in them which means the grinding has been a waste of effort. Pitting usually only occurs if rust hasn't been treated quickly, which is a must do.
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