What is the minimum standard for abrasive cleaning on the underside of surfaces?

The minimum standard for abrasive cleaning on the underside of surfaces is SA2.5. This level of surface preparation involves the removal of all rust, mill scale, and foreign matter to achieve a near-white metal surface, with some staining remaining. It ensures that there is adequate preparation for the application of protective coatings, which is crucial in preventing corrosion and ensuring longevity.

SA2, while also a standard for surface cleanliness, permits a bit more residual contamination compared to SA2.5, which can be detrimental to the adherence and effectiveness of protective coatings. SA1 is a much lower standard that allows for visible rust and scale, while SA3 requires a completely clean surface, which may not be feasible or necessary for all applications. Therefore, SA2.5 represents the optimal balance for achieving effective surface preparation in most situations, especially for the underside of surfaces where protection from environmental exposure is critical.