While the AISC Code of Standard Practice Section 6.5.2 calls for the removal of loose rust, loose mill scale, etc., the lack of specific definition (especially as to what constitutes "loose" mill scale) leaves the acceptance criteria subject to varying interpretation for both SSPC-SP2 (hand tool cleaning) and SSPC-SP3 (power tool cleaning). A mutually acceptable standard should be agreed upon by the owner so that the architect or engineer may knowledgeably design the paint system and the fabricator may realistically furnish the degree of surface preparation required.

As stated in SSPC-SP6 (commercial blast cleaning) Section 2.2, "staining shall be limited to no more than 33% of each square inch of surface area and may consist of light shadows, slight streaks, or minor discolorations caused by stains of rust, stains of mill scale or stains of previously applied paint. Slight residues of rust and paint may also be left in the bottoms of pits if the original surface is pitted." Because specifying this requirement for each square inch is impractically restrictive, AISC recommends that this requirement be applied instead to the total surface area.

last modified 18 September 2002

As stated in SSPC-SP10 (near-white blast cleaning) Section 2.2, "staining shall be limited to no more than 5% of each square inch of surface area and may consist of light shadows, slight streaks, or minor discolorations caused by stains of rust, stains of mill scale or stains of previously applied paint." Because specifying this requirement for each square inch is impractically restrictive, AISC recommends that this requirement be applied instead to the total surface area.

last modified 18 September 2002