Hi all. Just noticed this while washing the car today.

What’s the best way to nip this in the bud?
The metal seems OK, no rust on the inside.

 

There is a product called Rust Mort, you can paint on and it converts the rust to an inert form. It's basically phosphoric acid, converts iron oxide (rust) to iron phosphate.

 

Phosphoric acid is what I use. I think it's 35 or 40%. If there's flaking or thick rust,, I grind it or do a heavy sanding first. Otherwise, it's light sand, phosphoric acid, possibly another light sand and another coat of phosphoric acid, leave overnight, paint.

Some people say that you should wash it off or neutralise it, I never have and not had any problems. It's certainly no worse than etch primer.

 

I use Hammerrite rust remover gel. As others have said paint it on wash it off and paint with the colour of your car.

 

Nexa rust remover is being advertised

 

I wanted to say that's not rust, this is rust - and nothing like as bad as the one from the other side. After a long period of cutting, adjusting and re-drilling holes, the replacement spring hanger, that's the one at the top, fits adequately and today I started welding it in place.

 

It does not really feel or look like rust but the colour and the position made me believe that it must be. I have tried cleaning it but is does not clean off.

 

If phosphoric acid makes it go black, it is - or was - rust.

 

All serious rust starts like this, something that doesn't look too bad. However leaving it to fester is not a good idea.

My method for dealing with this in the past was to first make sure I had some rust remover in the garage, something like Jenolite. This is, essentially, phosphoric acid. Sand the area with a quite coarse paper. Its now possible to buy "opencoat" paper that one uses dry. Once you got most of the rust off, apply the Jenolite with a brush. You could use the jelly-type removers as this is a vertical surface, but continual application of Jenolite works well enough. Your aim is to get rid of ALL the rust that is there, not coat over it with "magical" rust products, IMHO, these don't work ! After removal of all the rust, a process that is quite time consuming, (make sure you have tea/coffee/beer, and a nice seat to sit on while you wait), you can apply a zinc-rich primer, then normal primer, then topcoat. It should last a reasonably long time, but that area is very vulnerable to road grit etc thrown up by the wheels so maybe before you apply topcoat, apply some body-schutz, which puts on a flexible layer to resist stone attack, then topcoat. However it is inevitable that you'll have to deal with places like this on a regular basis, depending on mileage per year and when you drive the car.