When a sufficiently hard abrasive particle strikes steel, it deforms the surface into a valley and pushes up peaks. The distance between the top of the peak and the bottom of the valley is known as the depth profile.
In the U.S., the depth profile is measured by mils – thousandths of an inch. In the metric system, the micron(one millionth of a meter) is used.
1 mil = 25.4 microns.
For optimal adhesion, the applied coating should completely fill the valleys and cover the peaks. The deeper the profile, the more anchoring occurs. However, if the profile is too deep, the peaks can protrude beyond the surface of the coating, causing pinpoint rust and premature failure of the coating. In some cases, the contractor may be required to go back over the area with a finer abrasive to reduce the surface to specified profile depth – a costly mistake.
Generally, the correct profile depth will be 25-30% of the dry film thickness of the total coating system. For most industrial coatings, the typical steel profile is between 2-3 mils, not normally exceeding 5 mils.
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