One of the things about electric welding  that  I've never really solved is how to passivate  the weld area for good paint adhesion.    I find my self grinding down flush, sanding the area and applying phosphate prep before I can trust the surface not to react later on and spoil the appearance.   Walking around and looking at painted and welded steel it seems that often others have the same problem.

Any short cuts? 

What kind of reaction are you getting? Passivation is for stainless steels to eat the iron that is left on the surface after machining to improve corrosion resistance.

Painted welds always seem to rust first and fast.   The metal is more reactive because to the heat applied.  I've noticed that some professional Industrial painting companies don't seem to have a problem.  However,  a lot of the house painter jobs seem to rust.  I started grinding and phosphate years ago. 

Surface prep, and a good primer go a long way towards a good result. Look into automotive applications for rust prevention. Many rust removers are phosphate based like Naval Jelly which is gelled phosphoric acid, and they leave a coating behind that helps prevent rusting. 

Take a look at a product called POR 15. It actually works best on lightly rusted or porous surfaces. It reacts with humidity in the air and actually penetrates and seals the surface. I buy the pint size put what I need in a cup and the rest I transfer to a mason jar to seal it. 1 drop of sweat or wate in a pint can and the next day it will be solid. Learned that the hard way. Make sure the sealing areas on the jar are clean with no paint on them or it will be sealed for good!

What kind of rod or wire are you using? I've always just ground welds smooth and painted them with a good quality enamel or in some cases a 2 part acid etch epoxy. Using a phosphoric acid prep works well, anything from Ospho, Naval Jelly or just brush on phosphoric acid and neutralize. The black patina is "phosphate" or "phosphorous oxide" (can't recall the correct term and I'm not looking it up) The black patina is porous and stops rust in it's tracks.

There's another thing about welds that isn't common knowledge, no secret just not common. A layer of paint on welds is an early warning system, like stress bands in cable or rope. The highest stress points in a fabbed structure are the joins. Joins are the most likely to initiate failure. Here's how paint on welds works. As the joint begins to fail the material moves on opposite sides of the failure and the paint starts to peal.

The other guys I worked with, in the office and on the drill crew thought I was a magician in that I could spot a crack in the drill tower as soon as it started to form. Sometimes I ground and welded them immediately others I could leave it till we turned it in for service at Heavy Duty shop.

Paint pealing from welds could simply mean they're flexing and might just need to be a little heavier or perhaps gusseted.

Frosty The Lucky.

Thanks for the information. guys.  I'll look for POR15 ,  I use 6011 for 7018 depending.

look  for core seal Its better than Ospho I use it here on the west coast

& a good paint primer is XO Rust rusty red primer a True Value product  only