Understanding Surface Profile

In the industrial and protective coatings industry, metal surfaces are blasted not only to remove corrosion or old coatings, but to generate a surface profile prior to re-painting. In some industries a surface profile is achieved through chemical etching or mechanical abrasion. But, regardless of the method, the surface profile increases the surface area of the metal - and it is this increased surface area which provides a key for the coating to adhere or stick to.

Surface profile should not be confused with roughness. Surface profile is a measurement of the peak-to-valley height. Surface roughness, on the other hand, is the combined measurements of the surface profile and the frequency of the peaks across a linear length (also known as the peak count). Surface roughness is measured using a stylus instrument.

Now that we have defined surface profile as the peak-to-valley height, why is it important for the coatings industry to measure it?

Quite simply, to avoid corrosion. Corrosion is typically caused when three things come together – a ferrous material (in our case the steel substrate – although it is worth noting that non-ferrous materials can also corrode), oxygen (from the air) and moisture. If you can remove just one of the 3 elements, corrosion (or more precisely aerobic corrosion) simply cannot happen. Applying a coating to the steel provides a barrier between the steel and both the air and moisture, preventing corrosion. So if the coating is damaged, or simply rolls off the surface due to poor adhesion, then the steel will rust, corrode, and in time weaken the structure. Not exactly ideal if you are coating a bridge for example.

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