I do a lot of repair on aluminum dumps used to haul anything farm related...lime, fertilizer, grain, manure, ect. Most of these trailers were used and abused long before they got life on these farms. You never really know how "bad" the little repair might be until you grind, wheel, solvent, heat up (usually not needed), and then finally strike an arc. Most of the stiffener ribs and any unwelded seam are full of crap that does not like to be welded. Once you start welding, what ever is in deeper or under your weld area will start getting sucked in, you’re completely in line with your grind weld grind grind weld grind weld grind grind weld.