Author: Ian Church in: Painting and Coating
Most finishing problems don’t start in the spray booth. They start when the actual film thickness on parts isn’t consistent, and nobody notices until defects show up at inspection or, worse, at the customer. One part comes out thin on the edges, another is heavy in the recesses, and suddenly you’re dealing with rework, scrap, higher material use, and questions about your quality controls. Film thickness isn’t a technical detail. It’s the difference between a reliable coating process and a line that constantly battles texture issues, coverage problems, and failed audits.
Film thickness, put simply, is the measured thickness of your applied coating, typically in mil for powder and paint, or Microns for OEM and spec-driven work.
Two categories matter: Wet Film Thickness (WFT) and Dry Film Thickness (DFT). WFT is measured right after application and used mostly in liquid paint shops. DFT is measured after curing. This is what your customers care about and it’s what most powder shops track.
Most SMB shops operate within a target range. For powder, that is often 1.5 to 3.0 mil depending on material and customer requirements. The challenge is hitting that range repeatably across different part geometries, operators, colors, and shifts.
Shops often blame operators for coating issues, but most defects trace back to powder coating film thickness variation. When film build is too low, you see poor coverage, edge thinness, and adhesion failures. When it is too high, you see orange peel, runs, sags, and cure problems. Inconsistent build also makes color control harder because thicker film requires more heat to fully cure.
Once you view defects through this lens, the pattern becomes obvious. The operator is not the issue. The lack of coating quality control is the issue. It’s not about “dialing in the gun.” It’s about having predictable, repeatable film thickness across operators, shifts, product mixes, and part geometries.
Most variation comes from a combination of six areas:
Deep pockets, tight corners, and heavy sections produce thick or thin areas due to Faraday cage effects and uneven heating.
Gun distance, angle, overlap, traverse speed, and rhythm all influence film build. Even trained painters struggle to stay fully consistent.
Powder flow, atomizing air, KV settings, microamps, and pump condition all change how much material reaches the part. Small changes add up.
Booth pressure, humidity, temperature, and conveyor speed can shift film build by a large amount without anyone noticing.
If one area of the oven is hotter than another, film thickness differences become appearance and adhesion problems after cure.
Different powders and paints have different target ranges and application behaviors.
None of this is news to painters. The issue is that most shops do not have a structured method to keep these variables under control.
Most finishing teams rely on a combination of:
A thickness gauge for DFT measurement
Periodic in-process checks at the booth
Calibration when they remember
Visual inspection when time is tight
A lot of trial and error
This approach can work if products are simple and defects are rare. It does not scale in high-mix environments, with geometry variation, or with demanding customers.
High-performing paint and powder operations do five things consistently:
Recipes per part family and per color remove guesswork and stabilize film build.
Visual diagrams or digital work instructions highlight edges, recesses, and features that need extra attention.
Several readings per part across different surfaces give a true picture of consistency.
DFT readings are captured digitally so patterns show up over time. This identifies issues like clogged pumps, worn nozzles, and drifting oven temperatures.
When readings are out of spec, the shop reacts quickly. They adjust settings, change line speed, correct the cure profile, or investigate material changes before defects stack up.
This combination reduces rework and scrap while improving consistency shift to shift.
This is where OnRamp naturally supports the process.
Your part records store the correct DFT range and any special instructions. Operators always know what to hit.
Barcode scans, operator prompts, and mobile data entry ensure readings are captured in real time. You eliminate paper, tribal knowledge, and work that disappears into a clipboard.
If a DFT reading is out of range, OnRamp can trigger an NCR, request an investigation, and record the corrective actions.
With structured data, patterns become clear. You can identify which shifts struggle with edges, which products run thick, and when equipment starts drifting. This turns film thickness from guesswork into a controlled process.
If a customer asks for evidence, you can immediately produce proof of measurement, targets, and compliance.
Whether you have full digital support or not, these steps improve consistency:
Take at least five readings across different features on complex parts
Calibrate DFT gauges weekly
Save gun recipes for recurring jobs
Use diagrams showing where to measure
Check powder age and humidity during long runs
Validate oven temperature at least daily
Log DFT readings by job and shift
Adjust line speed or gun settings based on measured data, not appearance
These steps help stabilize the process even in high-mix operations.
Film thickness control is not complicated, but it requires discipline. Shops that treat it as a core part of their quality strategy see fewer defects, lower material use, and faster cycles. Shops that treat it as an afterthought deal with rework, customer complaints, and unpredictable costs.
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