Overpainting Rust

[User]

 

[bpsmith]

Rust requires metal, air and moisture to form. If left to long, it bonds with the metal and that it.

Paints like Hanmerite work by sealing off the metal from the air and moisture element to limit further rusting. It won't eliminate it though.

Sadly, bike frames are susceptible to air and moisture on the inside too.

 

[sidevalve]

I have had success with one of the jelly type rust killers in the past [based on phosphoric acid I think - probably not allowed now] but it may just be a matter of luck. The only way I can think of is sand blasting but that's a bit harsh for bicycle bits.

 

[RichardB]

I have always found Kurust and Jenolite to be very effective. Brush on, leave, rinse off, dry. If you've got that black shiny surface, you've killed the rust and can fill and overpaint as you wish. But you can't stop the rusting process, just delay it, as all metals (and ourselves, of course) are trying to return to the earth they came from. For me, Hammerite is a last resort, as it covers rust well but does nothing to convert it to an inert substance as the others do. Rust continues to form, the Hammerite peels off, and it looks worse than before.

 

[snorri]

Grit blasting and epoxy coatings do a good job as long as there is no abrasion of the surfaces.
Offshore structures coated thirty years ago are still looking good.

 

[RichardB]

To add: yes, I believe Kurust and Jenolite contain phosphoric acid. It's the reason why Coca-Cola will remove rust - same stuff, just diluted. Not sure what they convert the rust to, but it's pretty stable stuff.

 

[Illaveago]

Treating bare steel with phosphoric acid known as bonderising, provides a rust inhibiting finish and also helps with paint adhesion. Sacrificial primers were used, often containing zinc so that the zinc would break down before the steel corroded based on electrolytic action between two dissimilar metals.

 

[sight-pin]

They sell a product in Spain called 'Aqua fuerte', It's basically Hydrochloric acid and will completely remove rust. You could try a janitorial supply over here for it.
Brush it on in the open because of fumes, (use goggles protective gloves) leave it to work, wash off with water and dry quick then primer it straight away.
If you go down this route please be careful with the acid as it will burn through most things. I would try a test area first.

Edit, just found this link about it. http://www.andalucia.com/forums/viewtopic.php?f=32&t=20361
I've bought before now as a toilet cleaner etc in janitorial supplies, it's just hydrochloric acid over here.

 

[Illaveago]

I have used the Hamerite rust removing gel and liquid on really rusty steel and chromed parts which seems to work well.

 

[earlestownflya]

loctite rust remedy is the automotive industry standard.

 

[Illaveago]

[QUOTE 4018326, membed9"]On the subject of using acids to convert rust, would battery acid (sulfuric ?) work ?

And as mentioned above, when the acid does turn the rust into that black stuff, what is it ?[/QUOTE]

I think sulphuric acid may have a detrimental effect on the steel if not thoroughly washed off. Not all acids provide rust inhibiting qualities. You only need to leave a piece of bright steel out in the rain to see the effect.

 

[RichardB]

[QUOTE 4018326, member: 9609"]On the subject of using acids to convert rust, would battery acid (sulfuric ?) work ?

And as mentioned above, when the acid does turn the rust into that black stuff, what is it ?[/QUOTE]
It turns ferric oxide (rust) to ferric phosphate, which is inert. Basically, it converts the rust but does nothing to prevent further rusting. The coating you put on afterwards does that.

 

[Ian H]

The reason rust treatments like Kurust fail is because they won't penetrate through rust scale, so the underlying metal isn't treated. It is essential to remove all the loose rust and rust-scale first, which can be pretty time-consuming.

 

[RichardB]

The reason rust treatments like Kurust fail is because they won't penetrate through rust scale, so the underlying metal isn't treated. It is essential to remove all the loose rust and rust-scale first, which can be pretty time-consuming.

Pretty sure that is covered in the instructions on the bottle. You can't throw a bottle at a rusty car and get a brand-new one, even if the adverts suggest it is that easy, but used correctly these products are fairly effective. As with everything, good preparation is most of the battle.

 

[Deleted member 23692]

White vinegar is superb for removing rust from small parts , but cider vinegar is even better