In the previous surface preparation post, I discussed steel making and the necessity for abrasive blasting to remove mill scale. But abrasive blasting, especially for maintenance work, cannot always be achieved because a facility owner may have restrictions on dust and particulate generation and there may be (and probably is) equipment operating 24/7. Plus, you need some extra room to accommodate abrasive blasting equipment and it may not be available. So what to do?
Fortunately, The Society for Protective Coatings has created surface preparation standards that allow the use of hand or power tools to prepare surfaces for painting. A putty knife or wire brush is an example of a Hand Tool; a needle gun or reciprocating impact wheel is an example of a Power Tool. For simply scraping off old, loose paint prior to repainting, a putty knife may be all that is needed. In fact, SSPC-SP 2 (Hand Tool Cleaning) is accomplished when any remaining paint cannot be removed with a dull putty knife.
Power Tool Cleaning in accordance with SSPC-SP 3 may provide better surface preparation because it could be faster to achieve a surface where any remaining paint cannot be removed with a dull putty knife. Like SSPC-SP 2 Hand Tool Cleaning, Power Tool Cleaning has the same dull putty knife end result.
For areas needing a more aggressive level of cleaning, the SSPC has two additional standards: SSPC-SP 11 “Power Tool Cleaning to Bare Metal” and SSPC-SP 15 “Commercial Power Tool Cleaning”. Both of these Standards go beyond SP 2 & SP 3 by requiring that a surface profile of 1.0 mil (1/1000″) be created. SP 11 is often used for small submerged areas being touched-up; SP 15 for similar areas that will not be submerged.
Note: avoid the use of wire wheels because they polish or burnish the surface making them slick and less likely to allow good coating adhesion. Ever wonder why the wires on a wire wheel do not rust? It may be because they’re oil-soaked. “Buzzing” over steel surfaces with an oily wheel will create contamination, not remove it!
Got a question about Hand or Power Tool Cleaning?