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Pre-existing anchor profile on blast cleaned steel substrate

October 28, 2011

I am a project manager and quality assurance director for an industrial coating firm, dealing mainly with lead abatement, abrasive cleaning and coating on complex steel structures. I have been certified through various NACE and SSPC courses.All coating experts know how important the anchor profile is when preparing steel to receive a new coating. That so called roughness on the steel will influence for the most part the adhesion of the first coating to be applied. Certain degrees of roughness (depth) are specified when doing abrasive cleaning on steel and standard methods to achieve it. My question is: What happens if the steel has been previously cleaned and painted (for ex. 20 years ago)? Shouldn't there still be an existing profile? Will the current abrasive cleaning add to the pre-existing depth? If yes, shouldn't the pre-existing profile be compensated for the new one? So if for example the current painting specification calls for 2-4 mils of profile to be achieved, should you shoot for 2-4? or should you first assess the pre-existing profile? Because if there is already a profile of average 2 mils, then you should only shoot for 2 mils.... I hope I managed to explain my question as good as I could. I really hope for an answer as this issue is starting to become more and more dominant within the bridge painting industry, especially when repetitious coating and corrosion maintenance on our Nation's steel bridges has reached many cycles within the past few decades. Thank you

MIKE VARVAKIS
PROFESSIONAL - BUFFALO, New York, USA

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I am not 100% sure of this, but my understanding of abrasives tells me that a blasted surface profile can only be as rough as the abrasive media being used; therefore, if you have a preexisting surface profile, you will not increase that RMS, but modify it to the abrasive being used. Naturally the hardness of a crystal structure media will achieve a different result than a softer glass bead media of the same size.

AF Kenton
retired business owner - Hatboro, Pennsylvania
October 29, 2011