TECHNICAL STANDARD
ASTM D4414
Standard Practice for Measurement of Wet Film Thickness by Notch Gages
ASTM International
2025
Current
WHAT DOES THIS STANDARD COVER?
Covers measurement of wet film thickness using notched gauges during coating application.
WHY IS IT RELEVANT?
WFT measurement can assist application control and can help an inspector or applicator assess whether the applied wet coating is consistent with achieving the intended dry film thickness. Do not treat WFT as a substitute for final DFT verification. The relationship between wet and dry thickness depends on the coating and relevant manufacturer/product information.
KEY INSPECTION CONSIDERATIONS
The practice addresses measurement of wet film thickness using notch gauges. Wet film thickness provides immediate feedback during coating application. The relationship between wet film thickness and expected dry film thickness can depend on the coating product, volume solids, application and other factors. Measurements should be taken while the coating remains wet.
WHAT THE STANDARD SHOULD NOT BE USED TO ASSUME
Wet film thickness does not itself prove final dry film thickness compliance. The relationship can be affected by product solids, thinning, application and surface geometry. The measurement also locally disturbs the wet coating. Final dry film thickness should be assessed separately where required.
PRACTICAL INSPECTION APPLICATION
Wet film measurements can be used as an in-process application control to help applicators assess coating deposition and make adjustments while work is underway. The applicable coating product and target application requirements should be understood. Final acceptance should use the project dry film thickness requirements where applicable.
RELATED TECHNICAL STANDARDS
RELATED TECHNICAL TOPICS
Wet film thickness; Coating application; Dry film thickness
RELATED EXPERTISE
Coating Inspection; Technical Consultancy
ABOUT THIS TECHNICAL SUMMARY
Paint Inspection Ltd provides this information to help inspectors, engineers, asset owners and contractors understand the practical relevance of commonly referenced protective coatings standards. This page is PIL technical guidance and does not reproduce or replace the published standard. Users should refer to the current published standard, project specification, coating manufacturer requirements and other applicable contract documents when establishing project requirements or acceptance criteria.
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OFFICIAL STANDARD
PIL technical summaries are intended to explain the inspection relevance of industry standards and do not replace the published document.
STATUS AND SOURCE VERIFICATION
Official ASTM catalogue checked 2026-09-23. ASTM D4414-25 is listed by ASTM as Active. CMS designation, title and edition checked against the official ASTM catalogue record.