Painting of Welds^★

In an experimental study by the Steel Structures Painting Council, 1146 welded, treated and painted test specimens were exposed to determine methods of obtaining improved paint performance over the weld areas of steel structures. During 30 months exposure in an industrial atmosphere, the performance of primers and primer-topcoat systems was observed on various types of welds which had been given various surface preparations and pretreatments before being painted. It was found that residues caused by the electrode coating should be removed from the weld area preferably by blast cleaning, before painting. When this is not possible, several types of pretreatments, such as washing with dilute chromic or phosphoric acid followed by a rinse, were helpful. Surprisingly, scrubbing the weld area with plain water was also very effective. The method of paint application had no effect, and there were only relatively small differences in the performance of various commonly used primers during the test period. Some types of welds were more easily painted than others, particularly those which had a minimum of alkaline deposit left by the electrode coating. Smoothness of bead and metallurgical factors appeared to be of minor importance. 5.4.5