best way to remove bubbling rust under the paint?

[mrmarcus]

well like the title says really. got a couple areas of bubbling rust under the paint and want to stop it now before it grows even more

[AndrewW-G]

Sand all the rust off, you may not like the end result though as you may end up having to patch the panel if the underlying rust has perferated the metal

[curlie467]

Like said, you would really have to cut the metal out, if its bubbling under the paint then it is starting from behind that panel, we have it on our 323, nightmare!

[NateWM]

Sand back everything. Use rust prevention treatment on any areas you sanded off, especially if you have had to take parts back to the bare metal.

Once the rust treatment has dried, clean and de-grease the affected area.

Apply filler. Make sure its hardened completely (if you have a garage, its best to leave it in there overnight) as you wont get a good smooth finish when sanding if the filler is only cured.

Once you happy with the shape of the filler, key the surrounding areas of paint near where you have repaired and then clean again.

Apply a few coats of good quality primer, leaving each coat to dry for a couple of hours. Check between each coat to make sure there are no imperfections, like "fish eye" or grit.

Once the coats of primer on one, make sure to flat the primered area to minimise orange peel affect.

[grumbledoak]

I believe the sequence is normally:
Sand the paint off
Wire brush the rust off
Realize the corroded area is far bigger than you thought
Curse your own foolishness for even starting this endeavour
Repeat with the sandpaper and wire brush
Rust treatment
Filler
More sandpaper
Re-paint

How old/special is the car?

[mrmarcus]

my plan is to sand/ grind the area then maybe put some of that "krust" or some other rust converter stuff on it and then just try and make good. Like you say, its coming from the inside so it will probably come back but need to do something with it rather than just leave it grow!

[NateWM]

Oh, its coming from the inside? Judging from your post, i thought it was just a little round the edge of the arch.

If thats the case, then i would reccomend cutting it out as soon as you can afford to. Atleast then, you would only need to cut out a small piece of metal, rather than replacing the outer and inner wings in a couple of years time.

[mrmarcus]

thanks guys. its a merc w210, plan on keeping for a few years yet so need to control this cancer thats appeared.

[JamesM]

When I did it I stuck a wire brush on the end of the drill and took it down to bare metal, then got the grinder out and ground off all the rust, put rust stopper stuff around the area, realised that the hole was bigger than I thought it would be, fibreglassed the hole, sanded it smooth, filled the dimples, sanded it smooth. Masked it off, primed it, undercoated it and then finally painted it and polished the repair into the rest of the paintwork.

It took me a couple of days to do properly on a relitavely small area so be prepared to spend some time doing it right.

[BE57 TOY]

Apologies to resurrect an old thread. Just wondered now the Krust stood up against time and whether the rust came back or not? (I'm in the same boat as you were). Many thanks.