Surface profile: what it is and why it matters
Surface profile, or anchor pattern, is the peak-to-valley roughness abrasive blasting leaves in steel. Coatings grip it mechanically: too little profile and adhesion suffers, too much and peaks can protrude through thin primers and become rust spots.
Specifications typically state a profile range - a common territory for many industrial systems is roughly 1.5 to 3.5 mils (40 to 90 microns), but the specified range for your project governs.
Measuring profile
The common field methods are replica tape, which is pressed into the profile and measured with a spring micrometer; depth micrometers with a pointed probe; and visual comparators. Replica tape additionally leaves a physical record that can be attached to the inspection file.
Profile is set mainly by the abrasive: size, shape, hardness, and velocity. Steel shot produces a rounded peened profile, grit an angular one, and mixed operating media drift over time as the working mix breaks down - which is why profile is verified on the work, not assumed from the abrasive purchase order.
Profile and DFT interact
A gage measures from the profile peaks, and coating must fill the valleys before it builds over the peaks. Deep profile under a thin specified primer is a classic conflict: the specified DFT may barely cover the peaks. When the measured profile approaches or exceeds the primer's specified thickness, flag it before application, not after.
CoatSpec stores the measured profile per work area and checks it against the profile range configured for the project, so an out-of-range profile shows up as a finding on the report.
Frequently asked questions
What surface profile do most coatings need?
Many industrial coating systems specify roughly 1.5 to 3.5 mils (40 to 90 microns), but it varies with the product and film thickness - thick high-build systems tolerate and sometimes want deeper profile than thin-film primers. The product data sheet and specification govern.
What happens if the profile is too deep?
Profile peaks can approach or protrude through the specified film, becoming points of premature rusting, and the extra surface area consumes more paint. Deep profile found before application should be raised with the contractor while it can still be corrected.
How is surface profile measured in the field?
Most commonly with replica tape read in a spring micrometer, or with a pointed-probe depth micrometer, following the test method your specification cites. Replica tape has the advantage of leaving a physical replica for the record.