Getting rid of rust stain

[Boatwayupnorth]

Owning a steelboat means fixing rust. That's just the way of things. This time on the targa. Sun was shining and promised to keep doing so for some days (which is rare, here way up north). In my neverending wisdom I got to it, angle grinder, flapdisc, epoxy primer and two-part urethan. Done it before and will do again. A light breeze blew, halv the dust up my nose and the other halv over my deck (once white). Two days later rust blooms appeared and I can't get it of them.
See pictures. Have tried vinegar without success. A compassionate neighbor suggested Coca Cola. Will try that tomorrow.
Has anybody had the same problem? And solved it? Anybody? PLEASE!

[Paul Elliott]

Oxalic acid works well. You can get rust stain remover products that contain this, or you can get oxalic acid crystals labeled "wood bleach" at a hardware store.

For what it's worth, I've used this on fiberglass, never painted steel.

[newhaul]

I scond the oxalic acid it works wonders.
Another common way to find it is "bar keepers friend."

[David M]

Use oxalic acid but use it sparingly and diluted out. Don't let it dry on the rust. Do multiple applications if needed. It can have a bleaching effect on paints and gelcoat.

[FionaJC]

I love oxalic acid for cleaning paintwork, wood and fibreglass. I buy it from ebay as crystals and add water. I also mix it with wallpaper paste to make a sticky gel. It will hurt on exposed skin and cuts so wear plenty of protection including eye. Then wash it off with water.

[wjhutchings]

Originally Posted by Boatwayupnorth

Owning a steelboat means fixing rust. That's just the way of things. This time on the targa. Sun was shining and promised to keep doing so for some days (which is rare, here way up north). In my neverending wisdom I got to it, angle grinder, flapdisc, epoxy primer and two-part urethan. Done it before and will do again. A light breeze blew, halv the dust up my nose and the other halv over my deck (once white). Two days later rust blooms appeared and I can't get it of them.
See pictures. Have tried vinegar without success. A compassionate neighbor suggested Coca Cola. Will try that tomorrow.
Has anybody had the same problem? And solved it? Anybody? PLEASE!

Having spent all of my career working on ships, the Mates curse are rust stains, to remove the stains best use a proprietary rust stain remover which are all derivatives of phosphoric acid as is Coca Cola which why your friend said use it, unless you feel confident enough to purchase the concentrated acid and dilute yourself, draw back being if don't dilute enough it will strip your paint off, too much and it won't do the job, I know this from bitter experience. Just paint it on, leave for about five minutes give it a scrub then fresh water wash off, with a high pressure washer if you have one.It is important you remove any traces of the rust stain remover as it will continue to etch the paint if you don't. This will remove the stain but not the cause, there are some things which will always weep rust bolts and nuts being the favourite, if cause of stain is not a nut or bolt, remove the rust in time old fashion, paint with rust killer found in any automotive parts shop, once dry repaint as normal that should hold the rust back for a year or so. Beware rust killer turns everything it touches black but it will wash off.

We I first went to sea we used to paint the decks with raw linseed oil after chipping them, leave that to dry and then paint as normal, that will really hold the rust back but it is expensive.

[mannix2]

How about Naval Jelly?

[Mithril Bham]

Dealing with the same thing all the time. This may be a stupid question but the rust must come from somewhere. It seems that grinding down to bare steel then prime, then coat would keep that from happening again? What am I missing?

[wjhutchings]

Originally Posted by magellanyachts

Dealing with the same thing all the time. This may be a stupid question but the rust must come from somewhere. It seems that grinding down to bare steel then prime, then coat would keep that from happening again? What am I missing?

It most could be to do with the way the edges are feathered back and how much over lap you give to the new coat of paint, also remember primers are not waterproof so if the area to be painted gets rain wet between priming and undercoating unless well dried off will mean you trap moisture between the plate and the first coat of paint which set off the corrosion cell again.

Another reason could be if this is happening along a weld line the rod used for welding was not compatible (I.e higher or lower on the periodic table) with the steel plates it is welding together. This will set up electrolytic corrosion between the weld and the plates, the same could be true of the plates themselves if they contain an impurity

[wjhutchings]

Originally Posted by magellanyachts

Dealing with the same thing all the time. This may be a stupid question but the rust must come from somewhere. It seems that grinding down to bare steel then prime, then coat would keep that from happening again? What am I missing?

It most could be to do with the way the edges are feathered back and how much over lap you give to the new coat of paint, also remember primers are not waterproof so if the area to be painted gets rain wet between priming and undercoating unless well dried off will mean you trap moisture between the plate and the first coat of paint which set off the corrosion cell again.

Another reason could be if this is happening along a weld line which it appears to be in your photographs, the rod used for welding was not compatible (I.e higher or lower on the periodic table) with the steel plates it is welding together. This will set up electrolytic corrosion between the weld and the plates, the same could be true of the plates themselves if they contain an impurity , if either is the case not much you can do, except in the case of the weld have it gouged out and rewelded with compatible rods

[arthur.watson.1]

Practical Sailor did a test and comparison of several name-brand rust stain removers and their winner was Starbrite Rust Stain Remover. I can't remember what the active ingredient of this product was, probably oxalic acid).

[inchcailloch]

Whilst never having used another form of rust remover, so I am unable to compare, I always have at least one bottle of "Starbrite Rust Remover" on the yacht. I find it deals with all rust I come across on my yacht which is fibreglass rather than steel yacht but for me most effective.

[andy marsh]

A friend once told us an acount of her going into IGR chandlers in Nidri Greece.
This is was when Danny was still with us, sadly he has passed away now.
She said to Danny i have a problem?
Danny said fire away!! she said how can i remove stains from my knickers. 😨
he laughed. 😄

It turned out she had a Bavaria and her clean nickers had layed against the steel coated screws in the over head lockers that had started to rust.

He handed her some oxalic acid that did the trick.

So lesson to all Bavaria owners. Dont put your white panties in the over head lockers or they may get stained. 😉 and yes oxalic acid will remove rust stains from your knickers.

[farmall.dude]

When I was a teenager, more than a few years ago, I'd use Muratic acid to remove surface rust from car doors, fenders and such. The kind you get from a pool supply store. Spritz it on, let it set a minute or two and rinse it off with fresh water. The trick is to dry it off and immediately paint it or do some other form of rust protection because it would flash rust in a very short time. Less than an hour if I remember right. It might not be the best solution because I don't know what it would do to the surrounding surfaces. You would definitely want to test it in a small inconspicuous area first.
I've also used CLR to get light rust off, but it too has to be rinsed, dried and painted immediately afterward.
Good Luck!

[Camille1]

Oxalic Acid is the business and way less expensive. Experiment with dilution, maybe 1:5 of water. it depends on the concentration in the bottle you buy. If you buy crystals try 25 grams to half a litre of water and give it ten minutes to show results.

Next time you grind mild steel, I'm sure you will remember to hose down the deck thoroughly afterwards. Same with wire wool and wire brushing. Best always to use 316/A4 brushes and wool.

muriatic acid is also called Hydrochloric acid; not much good at clearing rust. likewise Phosphoric acid. However, Phosphoric Acid and associated products are widely used for protecting mild steel from rust. Phosphoric Acid need care as it destroys the nerve ends in fingers without any stinging or feeling.