The use of aluminum for fabricating large structures is increasing rapidly. Recent developments in the transportation industry have spurred this demand. The main joining method used for these aluminum fabrications is gas metal arch welding (GMAW). A major problem encountered with GMAW is hydrogen-induced porosity. Prior to this study, very little published research was available to help the process engineer establish procedures that ensure porosity free welds. While many factors influence porosity, surface preparation has been largely ignored. This research shows that proper surface preparation has a significant effect on porosity formation.