Introduction
Surface profile is one of the most important factors in coating performance. A properly prepared surface gives the coating something to anchor to, improving adhesion and long-term durability.
But what happens when the surface profile ends up too high?
Most coating manufacturers specify a recommended profile range, often something like 2–4 mils or 3–5 mils, depending on the coating system. These ranges are designed to ensure the coating can fully wet the steel surface and adequately cover the peaks created during abrasive blasting.
When the profile exceeds those limits, problems can begin to appear.
Why Excessive Profile Can Be a Problem
At first glance, a deeper profile might seem beneficial. More texture should mean better adhesion. In reality, once the anchor pattern becomes too aggressive, several issues can develop.
Insufficient Coating Coverage
When peak height exceeds the applied coating thickness, the coating film may not fully encapsulate the tips of the profile. Even when the average film thickness meets specification, the highest peaks can remain only thinly covered.
Early Corrosion Initiation
Those poorly covered peaks can become the first locations where corrosion begins. Moisture and oxygen can reach exposed or poorly protected areas of steel, leading to early failures such as pinpoint rusting.
Visual Example
The illustration below shows the relationship between surface profile height and coating thickness.
Left: Acceptable profile where coating thickness exceeds peak height and creates a continuous protective barrier.
Right: Excessive profile where peak height exceeds coating thickness, leaving exposed areas that can initiate corrosion.
What Causes Excessive Profile?
Several conditions in the field can unintentionally produce a profile that exceeds specification.
Using abrasive media that is too coarse
Excessive blasting pressure
Holding the blast nozzle too close to the surface
Repeated blasting passes in the same area
Changes in recycled abrasive characteristics over time
What Should Inspectors Do?
When profile readings exceed the coating manufacturer’s limits, the issue should be addressed before coating begins.
Re-blasting with Finer Media
Blasting the surface again using a finer grit or spherical steel shot can help reduce peak height and produce a more suitable anchor pattern.
Adjusting Blasting Parameters
Reducing blast pressure, increasing nozzle distance, or changing the blast angle can help control the profile being generated.
Mechanical Surface Conditioning
In some cases, high peaks can be reduced using light grinding or mechanical surface conditioning. When this approach is used, the surface may need to be reblasted with finer abrasive afterward to ensure the final profile still meets specification.
Consult the Coating Manufacturer
If the profile cannot reasonably be reduced, the coating manufacturer may approve a higher minimum film thickness or recommend a coating system designed for rougher surfaces.
Final Thought
Surface profile is often treated as a simple pass-or-fail measurement, but in reality it is a balance.
Too little profile can reduce adhesion.
Too much profile can prevent the coating from fully protecting the steel.
A coating can only protect what it completely covers. When peak height exceeds coating thickness, those exposed areas become the first place corrosion begins.
The goal isn’t the biggest number on the gauge.
The goal is a profile the coating can fully encapsulate.
Roberts Corrosion Services, LLC
Established in 2011, Roberts Corrosion Services, LLC delivers comprehensive, turn-key cathodic protection and corrosion control solutions nationwide. Our end-to-end expertise encompasses design and inspection, installation and repair, surveys and remedial work. We provide drilling services for deep anode installations and a full laboratory for analysis of samples and corrosion coupons, as well as custom CP Rectifier manufacturing.
While our initial focus was on the Appalachian Basin area, we complete field work all over the US. We are a licensed contractor in many states and can complete a wide range of services.
Our biggest strength is in our flexibility for our clients. Solutions and Results.
Let us know how we can help.
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