Surface preparation is a critical step in ensuring reliable bonding, coating, and adhesion performance. It involves modifying a material’s surface to improve its chemical and physical compatibility with a substrate. Among the various surface preparation techniques, abrasion is one of the most common. Abrasion involves mechanically roughening or cleaning a surface, typically using sandpaper or similar media, to remove contaminants, oxides, or weak surface layers and to increase surface energy for better adhesion. However, when abrasion is performed manually without quantifiable validation or process control, it can introduce significant variability. Operator-dependent factors, such as speed, duration, applied pressure, and technique, can lead to inconsistent surface conditions. Without objective measurements to verify surface quality results, it makes it difficult to troubleshoot adhesion failures or optimize downstream processes.
Yet, even with well-defined procedures and standardized methods, surface preparation remains susceptible to a frequently overlooked source of failure- human variability. In practice, a significant number of adhesion issues can be traced back not to the materials or the chemistry, but to inconsistencies in how the surface was prepared. This study explores how the human element influences surface preparation results and why understanding this hidden variable is essential to achieving consistent, high-quality adhesion.
In this study, a post-abrasion surface state was quantified using water contact angle (WCA) measurements. WCA provides a practical way to estimate a material’s surface energy, providing insight into how clean or activated a surface is. Surface energy allows us to evaluate how likely a surface is to produce favorable adhesion results.
Eleven operators were provided with the same set of materials- an aluminum coupon and a piece of sandpaper- and given identical instructions outlining the abrasion procedure. Each operator measured their aluminum coupon before and after abrasion with Brighton Science’s BCMobile device.
The results of the hand abrasion study are illustrated in Figure 1, which compares WCA measurements for each operator’s abraded sample against the as-received surface condition. Comparing average WCA and standard deviation (point-to-point variance) across samples demonstrates how the slight differences in technique (pressure, number of passes, direction of sanding) can lead to significant variance in the surfaces produced.
Fig. 1: Box plot showing pre- and post-abrasion WCA measurements across 11 operators (labeled Operator A – Operator K).
The purple shaded region on the box plot (40 – 50°) illustrates Brighton Science’s ‘typical threshold for adhesion’ for aluminum substrates. * Samples whose average WCA values fall above this threshold (50°) are more likely to result in poor adhesion in most applications.* Samples whose average WCA values fall within this region (40 – 50°) and show a large standard deviation (>5°) are more likely to result in unpredictable adhesion results in most applications.* Samples whose average WCA falls below this region (<40°) with standard deviations <5° are more likely to result in favorable adhesion results in most applications.*
When samples fail disastrously or consistently, it’s usually easier to pinpoint the gaps in the process. The real challenges arise in processes that operate at the edge of their capabilities. These processes will produce favorable results most of the time, except when subtle changes (weather, materials, operators) quietly influence the outcome.
When surface-affecting variables aren’t controlled or measured, failures are not only more likely to happen, but they also appear random and difficult to trace. In this study, nearly half of the operators produced surfaces that fell into this borderline category.
While the experiment demonstrated that manual abrasion produces a wide range of outcomes, understanding why this variability occurs is essential for improving consistency in surface preparation.
Even when operators follow the same written procedure, subtle variations in execution can dramatically alter the surface outcome. A procedure defines what should be done- such as the type of abrasive, number of passes, and direction- whereas execution determines how it’s done in practice. It’s within this human element of execution that variability arises.
Several key factors contribute to variability:
These variations compound to produce significant differences in WCA, as observed in the experiment. Even small inconsistencies- imperceptible to the naked eye- can shift a surface from being well-prepared for adhesion to one that underperforms.
Variability in manual surface preparation has real consequences in manufacturing and quality control. When abrasion isn’t performed consistently, it can lead to:
These outcomes show that it’s not enough to standardize the procedure; the execution must also be controlled. True process reliability comes from ensuring every surface is prepared the same way, every time.
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Reducing operator variability in surface preparation begins with acknowledging that true consistency requires both technique and measurable control. Without quantifiable validation, variation is inevitable- even among skilled operators. The following strategies help ensure every surface is prepared to a known, repeatable standard:
At Brighton Science, our tools make it possible to quantify and control these critical variables. When you can assign numerical values to surface readiness- including surface energy- you move beyond assumptions. This objective data empowers manufacturers to create repeatable, validated processes and produce reliable adhesion every time.
As the saying goes: “you can’t control what you don’t measure.” In surface preparation, that principle is especially true.
Surface preparation isn’t just about following a procedure- it’s about producing consistent, measurable results that reliably support adhesion. Even the most detailed work instructions can fall short if execution varies from one operator to another, or one day to the next.
By incorporating quantifiable measurements into surface preparation, manufacturers can transform a traditionally subjective process into a controlled, specification-driven one. When you can measure the state of a surface, you can control it. And when you can control it, you can train to it, standardize it, and scale it across operators, shifts, materials, and facilities.
Ultimately, reducing human variability is not about removing the human- it’s about providing them with measurable targets that eliminate inconsistency. Through measurement-driven process control, every bond becomes predictable, every result becomes repeatable, and every product meets expectations.
Fran Schute is a surface science specialist with a background in biochemistry and a passion for solving sticky problems (literally). As a Customer Success Manager at Brighton Science, she works directly with technical and manufacturing teams to translate and interpret surface energy data into process improvements. Fran is committed to ensuring her customers succeed by driving measurable advancements in production control, performance standards, and adhesion reliability.