Treating surface rust under car

[ashy90]

Hi,

What is the best method of treating surface rust under a car?
The areas that are covered with that thick squidgy type lumpy texture (bitumen? Epoxy coating?) are absolutely fine. It is the areas without this special coating such as the wheel wells and sills that are showing signs of rusting. Would attacking with a wire wheel, some anti rust primer or red oxide followed by some white/grey paint suffice?

 

[Danez]

Personally I'd use some bilt hamber hydrate 80. Just be sure to get rid of the loose rust first and you can paint over the hydrate 80 after it's set with some stonechip for extra protection

 

[MetalMonkey]

You will find the rust extends a lot further beneath the underseal than you expect.

My method for dealing with this is to chip/scrape the loose stuff off (needle gun is useful) - then wire wheel until you start to see clean non-pitted metal.
Then scuff the original factory sealer coating back further to clean it up but not to the point of removing it entirely.
Treat the rusty pitted areas with a rust preventer (I use phosphoric acid).
Clean very thoroughly with solvent/panel wipe
Epoxy the whole thing blending the repair it in to the original underseal, then topcoat with underseal.

 

[bricol]

Are you keeping it forever or just don't want it to deteriorate too much in the next few years?

If the latter, your suggestion works for me - just be carefull with wire wheeling - it tends to remove the loose stuff, and then polish the surface so it looks lovely and clean. However, if you drag something pointed across it, a flat screwdriver blade for example, if it leaves an orange line behind . . . its still rusty.

I would probably spot blast those areas after the wire brushing - removes the rust and keys the surface nicely for epoxy paint to stick properly. My 34 yr old, used daily, Lancia offers hope my approach works

I would be more worried at the moment at what looks to be missing bung at the bottom of that piccie though - lets all the thrown up spray, crap and salt into the inner sill structure, where it will sit nicely in the crevices at the bottom, holding moisture against the metal, giving you the opportunity to practice cutting metal and welding new back in a few years.

 

[marlinspike]

I'd wire brush/wire wheel/powerfile as much of the rust off as you can first. It might well be worse than it looks. Hydrate 80 to treat any pitted rust that you can't get out. Epoxy primer if you have it, otherwise a decent primer from a spray can or brush on. Then grey stonechip. Lots of brands do it in grey:

grey stonechip

grey stonechip

www.eurocarparts.com

 

[Ross365]

"Red Oxide" no longer means anything other than the paint is red. In the past, it described paints which contained lead oxide, which was a good corrosion inhibitor, but now regarded as too toxic for use.

I'm a big fan of paints containing zinc phosphate inhibitor; this is my current favourite https://www.palatinepaints.co.uk/product/carboxide-metal-primer/

 

[ajlelectronics]

"Red Oxide" no longer means anything other than the paint is red. In the past, it described paints which contained lead oxide, which was a good corrosion inhibitor, but now regarded as too toxic for use.

This needs to be proclaimed widely.

 

[arther dailey]

? thought you were meant to paint it on not chew or lick it

 

[ajlelectronics]

? thought you were meant to paint it on not chew or lick it

But nanny always knows best (apparently).

 

[Shedendman]

As someone has asked,are you keeping the car for ever or you just want it to last a few more years?
The few more years solution..........................
That thick squidgy type lumpy texture stuff as you put it is never all right,never has been,never will be,only needs the slightest of crack and water will get behind it,get most of it off(if not all) best attack at first is an old chisel or screwdriver,wire brush the rest off
It doesn't appear to look that rotten(but dont be fooled by that photo) that rusted area needs to cleaned up right down to metal,give it a poke,is it sound/solid? If it is just treat with a rust convertor phosphoric acid is fine,but i've been using this stuff and i'm happy with it,there is of course other brands

Pardon our interruption...

A good coat of primer over what you've cleaned,then smash in a PU sealant something along the lines of tigerseal or any other brand of polymer/polyurethane
Next good few coats of stonechip shultz other brands are available
OH and get a rubber grommet for that hole,your just asking for trouble there big time
Again,this'll give you a few more years,maybe,if you want it for much longer then thats a different ball game all together