PAINTSQUARE BLOG

Ever hear anyone state with great authority that you can't know what surface preparation was performed after the paint has been applied? You know: Once you paint that steel, you just can't tell how well it was blasted—or even if it was blasted at all. Right?

Um, no, not exactly. 

I'm sure there are many contractors and owners who might think that this is true, but look at enough jobs where the paint was applied over improperly prepared surfaces and you start to recognize all kinds of interesting patterns.

No Fooling the Eye

Usually, it is easy enough to tell when a painted surface has been blasted to anything less than SSPC-SP 6, Commercial Blast Cleaning. SSPC-SP 6 allows only staining to remain. This means there should be no remnants of mill scale, rust, or paint on the blasted surface.

All of these deficiencies are easy enough to see with the naked eye. Islands of intact mill scale look like little raised plateaus. Rust and paint look like little hills or mountain ranges. Usually, you can even get a photograph that is convincing enough to prove your point.

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Mill scale left on a surface before painting will quickly—and oh-so-obviously—reappear afterward.

In other cases, it may be difficult to prove your case with a photograph of the intact paint. Or sometimes, you may suspect that the surface preparation was not up to snuff, but you can't be sure.

What to do?  Enter the Magic Hammer.

Hammer Time

We consultants are a crude lot, willing to prove our point by any and all means necessary. The exact brand and type of hammer that I use is a trade secret. Others have been schooled in the art of the Magic Hammer, so you can ask them if you like—but I'm not telling.

The Magic Hammer is a sacred instrument. When wielded by a trained expert, it can reveal a contractor's deepest, darkest secrets—or, at least, what they don't want you to see. The Hammer is used to strike the painted surface with just the right amount of force needed to cause the paint to chip from the surface.

craigstephens.blotspot.com

A consultant's Magic Hammer is a secret and sacred instrument. This is not Tim Race's actual Magic Hammer.

In some cases, the paint chips have telltale remnants of mill scale, paint, and/or rust stuck to their undersides. Sometimes, the intact contaminants just lie there on the surface in all of their glory—bright orange spots or freckles of lead paint, grungy rust spots, rusty pits, stratified layers of rust, an occasional glove or small animal, bird droppings, animal scat, piles of dirt or blast media, and shiny black plateaus of mill scale.

Dirty Secrets

I have even found entire surfaces that were painted with absolutely no blast cleaning at all.  Pictures of said contaminants are generally more convincing after the paint has been removed. 

The Magic Hammer can also be used to survey areas that are suspected of not having been properly blasted. The obvious locations to check are those spots where the blaster must spend the most time to achieve the specified level of blast cleaning.

On a simple grade crossing highway bridge, there are several areas of interest. I will provide a detailed discussion of these locations in a future post (it's as bad as cheating on your spouse)—and how it's done. 

Profiles in Blasting

The Magic Hammer can be used to prove that a previously painted surface was blast-cleaned to less than an SP 6. However, the Hammer cannot be used to differentiate between SP 6 and higher grades of blast cleaning.

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Paint chips liberated by the Magic Hammer tell tales of poor surface preparation.

In some cases, the Hammer can be used to remove enough paint down to the substrate to determine the blast profile using a comparator or replica tape.

Deficiencies of the Magic Hammer can, in some cases, be overcome by using paint stripper and brass brushes to remove the paint down to the substrate. This should allow measurement of the blast profile, peak density, and percent staining or anything else about the blast cleaning that may have been specified.

ABOUT THE THE BLOGGER Tim Race Tim Race began his career in paint technology with the U.S. Army Corps of Engineers, where he was nicknamed “Paint Dude” by his future wife. He later served as a consultant, working for Corrosion Control Consultants and Labs and independently. Race received the SSPC Technical Achievement Award in 1998 and was named an industry Top Thinker by JPCL in 2012. After 30 years in the industry, he is now enjoying retirement and letting his wife do the heavy lifting. SEE ALL CONTENT FROM THIS CONTRIBUTOR