Getting rid of rust. What is enough?

[Engineer]

I just bought a clean bed for my truck, but in stripping the paint I have found some small rusty areas under the paint.

Most of the rust is no more than areas of about 1/8" diameter. The rust has resulted in minor pitting. How much effort should be enough to prevent the rust from returning? I have stripped all of the paint. What I have been doing is to sand the spots until the orange dust disappears.

Is this adequate or should I sand the whole area smooth? I figure the 2K urethane primer I am using will fill the pitting but should I worry about the base primer not sticking if I don't get deep enough with the sanding?

FWIW, my base primer is a wet sand able primer/sealer.

[werewolfx13]

Treat the pitted areas with a drop of Ospho (Phosphoric Acid solution)

[Elpresidente]

Just touch it with a grinder, use a bit of bodyfiller to flatten out any concave section that makes.

[Jason S]

What I have been doing is to sand the spots until the orange dust disappears

I've done the same thing when dealing with surface rust that has resulted in minor pitting.  My thoughts are that as long as there is good clean bare metal, there shouldn't be an issue with the primer sticking to the metal.

[Engineer]

Thanks guys. Kinda confirms what my thoughts were too.

After sanding out the orange dust it leaves a dark discoloration. Just making sure the primer/sealer will stick.

This is on the M-1008 bed I just bought for my '77 K-30 project if anyone is interested.

[jaredts]

The primer will stick, but if there is rust down in pits it will trap oxidation and spread later.  If the pits are deep you shouldn't grind it out either.  Media blasting, or some acidic rust treatment (usually phosphoric acid based) is required.  I've used a few different rust kutter type solutions--some are better than others.  I've found that aggressive use of a wire wheel on a die grinder or cup wheel on an angle grinder helps get a lot of the crud out of the pits.

[zieg85]

http://www.hi-litesolutions.com/for-sherwin-williams.html  is some amazing products, especially the AC-10 at the bottom.  Can't say enough good about their effectiveness.