Alkaline and hygroscopic welding flux byproducts deposited on weld seam and adjacent areas frequently are the cause of early failure of coatings on welds. Close observation by the author indicates many paint failures previously believed to have resulted from residual stresses in weld areas can be attributed to the effects of weld heat oxides, weld flux, spatter and weld flux fume deposits.
Careful cleaning of weld flux deposits from the weld itself and from adjacent areas either by impact tool, wirebrushing, pickling or best of all by sand blasting is recommended. A flame cleaning pass is recommended whenever moisture is present.
Extra thick vinyl pretreatment coatings followed by a mastic and finish coat are helpful in prolonging protection given metal from the environment when flux deposits are inadequately removed.
Preweld oiling of areas adjacent to welds will reduce time needed for removing flux byproducts to 25 to 30 percent of time required for cleaning areas not pretreated. Preweld oils must be compatible with paints to be used.
Grinding flat of exceptionally rough welds and weld striping to increase coating thickness are advocated.
