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TECHNICAL SPECIFICATION NO. 2 <br />COMMERCIAL BLAST CLEANING <br />2.01 SCOPE <br />This specification covers the procedure required for the commercial blast cleaning of <br />structural steel surfaces prior to painting or coating. <br />2.02 DEFINITION <br />Commercial blast cleaning is a method of preparing metal surfaces for painting or <br />coating by removing mill scale, rust-scale, paint, or foreign matter to the degree <br />hereafter specified, by the use of abrasives propelled through nozzles or by centrifugal <br />wheels. <br />A commercial blast cleaned surface finish is defined as one from which all oil, grease, <br />dirt, rust-scale and foreign matter are removed completely from the surface and all rust, <br />mill scale, and old paint have been completely removed except for slight shadows, <br />streaks, or discoloration's caused by rust stain, mill scale oxides or slight, tight residues <br />of paint or coating that may remain; if the surface is pitted, slight residues of rust or <br />paint, may be found in the bottom of pits: at least two-thirds of each square inch of <br />surface area shall be free of all visible residues and the remainder shall be limited to the <br />light discoloration, slight staining or tight residues mentioned above. Photographic or <br />other visual standards of surface preparation may be used to modify or further define <br />the surface if specified in the contract. <br />2.03 PROCEDURES <br />Commercial blast cleaning shall consist of the following sequence of operations: <br />A. Heavy deposits of oil or grease shall be removed by the methods outlined in <br />Specification SSPC-SP 1-63, "Solvent Cleaning". Small quantities of oil or <br />grease may be removed by the blast cleaning operation. If oil and grease are <br />removed by blast cleaning, the abrasive shall not be reused if such reuse is <br />detrimental to the surface. <br />B. Excessive rust-scale may be removed by impact tools, as outlined in <br />Specification SSPC-SP 2-63, "Hand Tool Cleaning", or SSPC-SP 2-63, "Power <br />Tool Cleaning", or by special blasting equipment. <br />C. The surface of the metal shall be blast cleaned to a commercial finish by any <br />of the following methods: <br />TS2-1 <br />y1 445 <br />