My brother, who used to work as a welder, brings over a metal hatch lid for me to fix. It's 1/8" sheet and it's got a crack about 3" long at the hinge. Sure Bro, no problem, follow me out to the garage... Hit it with the sandblaster to strip the paint around the crack, and then carry it over to the welder. He stops me and asks WTF I'm thinking? Tells me you are NEVER supposed to weld sandblasted steel, as the sand embeds silicone crystals in the metal, and it'll cause the weld to be brittle and crack. Really? I always wipe the dust away with a rag before I weld, but I've never heard this before. Just to make him happy, I made a couple passes over the damaged area with a wheel, welded up the crack, and sent him on his way. Like I said, he worked as a welder for about a year [a few years back], so I'm thinking he might know something about what he's saying... But I've never heard of this before. I was told that sandblasting is a good thing because it works the metal up to allow better penetration... Never heard about silicone contamination. Any thoughts?