Painting rusty garage door hinges in situ

[Lobster]

I'm taking advantage of the weather to paint my garage doors - long overdue.

The doors are hung on hinges like these:

Unfortunately they never got painted when originally fitted and are now very rusty (surface rust only; they are perfectly intact and strong.

I know that the best way to sort this out would be to remove the doors altogether and unscrew the hinges, however that's really not practical for several reasons and isn't happening, So, given that the hinges are definitely staying on and want painting (black), what's the best way forward? Hammerite, which says to paint straight on to rusty steel without brushing first? Or treat the steel with some chemical, and then prime and paint as usual?

Thanks

[Archibald Tarquin Blenkinsopp]

"very rusty" wants brushing whatever you use.

Phosphoric acid will then convert the rust to something paint friendly, it can be prmed and painted in the usual fashion. Halfords used to do a range of treatments for rust, virtually all of them used phosphoric acid in their makeup and some acted as primer too.

Cars have improved over the years, but Halfords may still stock a few lines.

Hammerite will do the job also, but "very rusty" means brushing I'm afraid. If the rust isn't securely affixed to the metal, then the Hammerite will not be firmly bonded either.

The doors should'nt have to be removed to remove those hinges, just don't do them all at once.

AB

[ss]

Can be bought cheaply on ebay.

[alan_m]

Paint first with Phoshoric acid and leave for 12 hours and then oil based paint.

[The Natural Philosopher]

Iron phosphate.

Tough and stable.

"It can be used in steel and metal manufacturing processes. When bonded to a metal surface, iron phosphate prevents further oxidation of the metal. Its presence is partially responsible for the corrosion resistance of the Iron pillar of Delhi.

Iron phosphate coatings are also primarily used as base coatings for paint in order to increase adhesion to the iron or steel substrate, and is often used in rustproofing as well. It can also be used for bonding fabrics, wood, and other materials to these surfaces as well. Iron phosphate coatings are usually applied as part of a painting or powder coating process."

In fact rusty iron/steel that has been phosphated with acid will probably be more resistant to corrosion than bare metal

[GB]

It might be cheaper to buy new hinges than to treat the old ones.

[tabbypurr]

But converted loose rust doesn't mysteriously bond itself well to the metal. I last used HCl it removes everything, but you can use phosphoric acid. As said, painting onto the rust won't work, it has to be removed.

NT

[GB]

On a practical issue, can you use this acid when the hinges are attached to the door?

[Archibald Tarquin Blenkinsopp]

Well you probably drink the stuff, or should be doing so if your water authourity hasn't replaced the lead pipework yet.

It makes your fingers black in high concentrations and takes the enamel off Ones teeth, but wood should survive a brief splash or two.

AB

[tabbypurr]

Since I have HCl, I would use it, it's way better, but be most careful to keep it off the wood. Pickling acid eats almost everything, including teeth & eyeballs.

Often hinge screws can be loosened so the hinge sits a little off the wood - then HCl could be used all over.

NT

[Archibald Tarquin Blenkinsopp]

HCL + Iron oxide = ferric chloride. Not nice, still very corrosive.

Posphoric acid + Iron oxide = iron phosphate, stable solid material.

As far as the reaction with bits of me goes, I would prefer phosphoric any day.

I seem to recollect that Coca Cola was once used for derusting purposes, no doubt before the company found they could get through the same number of teeth by reducing the acid levels and upping the sugar.

Might still be worth a try though :-)

AB

[tabbypurr]

there's the problem, it sticks to the workpiece but not that well.

For sure :) Such is diy.

I assume it's too weak by far.

NT