I dont weld without it. I bought eastwoods "bloxide", one of the few products from eastwood that really works for me. If you weld without it, wake up the next morning, and you can see rust all around the weld area. I dont scratch any of this stuff off before the weld. This primer has aluminum in it, so I guess it is conductive to the mig wire. Its nice becuase you can brush it on where you need it. I've been doing a lot of fab work on my project so I buy the metal sheets from lowes, home depot, etc. in the 8x16 or whatever size and degrease them, scotchbright pad em, then coat them with this stuff. I have sheets from last year that are ready to weld with no surface rust on them.