Thickness Survey and Adhesion Test on a Containment Floor
An inspector surveys 200 m² of epoxy floor coating specified at 12–16 mils DFT. The magnetic gauge was calibrated at the start of the shift on a certified shim. The inspector takes five readings in each 10 m² area. One 10 m² area averages 13.2 mils, but a single reading is 9.5 mils; another area averages 11.4 mils. The applicator argues both areas meet the average and asks for acceptance. The specification invokes SSPC-PA 2 and requires no individual reading below 80% of the minimum. A pull-off adhesion test in the low area gives 420 psi with cohesive failure in the coating. The floor is in a radiologically controlled area, and rework would require a new work permit.
1. Should the inspector accept the two areas? Apply the thickness criteria and explain the adhesion result's role.
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No. The 13.2-mil area has a single reading of 9.5 mils. The minimum is 12 mils; 80% of 12 is 9.6, so 9.5 is below the individual-reading floor, although only marginally. That reading must be rechecked with a calibrated gauge and the area mapped. The 11.4-mil area fails the average minimum of 12 regardless of individual readings.
Adhesion of 420 psi with cohesive failure is favorable but does not correct insufficient thickness. Adhesion and thickness are separate acceptance criteria; one cannot be traded for the other. The inspector should require repair of the 11.4-mil area and verification, and likely repair, of the 9.5-mil reading if confirmed. Rework in a radiologically controlled area needs planning, but schedule is not an acceptance criterion.
2. What measurement and documentation steps should follow before a repair decision is finalized?
Read the worked answer
Verify gauge calibration and surface condition; take additional readings per the specified grid and record each reading, not just averages. Check for gauge drift and substrate curvature. Mark low areas. If a reading is within measurement uncertainty, confirm with a second calibrated gauge or a different method.
Document the area, readings, gauge serial number, calibration date, and inspector. If repair is required, define the extent: abrade and clean and apply additional coating within the recoat window, or remove and recoat if low thickness affects barrier properties. After repair, re-measure and record. The nonconformance report should state the requirement, objective evidence, disposition, and closure. Because access is controlled, coordinate radiological work controls before repair.