Wet Film Thickness

Definition - What does Wet Film Thickness mean?

Wet film thickness is the thickness of wet paint or any coating film that is liquid based. Wet thickness is at its peak right after the application of coating. It decreases once volatiles and solvents from the coating film undergo evaporation.

Measuring wet film thickness is necessary to identify the amount of material that needs to be applied to achieve a particular dry film thickness that will give the best protection against damage, wear and corrosion.

Corrosionpedia explains Wet Film Thickness

Measurement of wet film thickness of paints or coatings applied on materials can be very beneficial in determining the appropriate thickness of dry coating. Almost all top performing and protective coatings should meet specific requirements for dry film thickness. Therefore, a direct relation exists between wet film and dry film thickness.

The dry film and wet film ratio is identified by the volume of volatiles present in the applied coating as well as permitted thinning. In flat coatings, the wet film thickness is usually lower than the dry film thickness. Taking a wet film thickness measurement at the point of application is ideal, as it allows film adjustments and corrections at the point of application. Making corrections once the film has undergone chemical curing or drying takes substantial time and labor, and could result in film contamination. Moreover, it may result in problems like reduced integrity and adhesion of the coating.

In order to measure wet film thickness, various gauges are used. The most common are:

  • Notched gauges - Suitable for non-even surfaces such as rough concrete blocks. They are also ideal for the field and shop, especially in identifying the estimated wet film thickness of commercial articles that have shape and size not suitable for other gauge types like thin edges, ellipses and others.
  • Pfund and Interchemical gauges - These gauges are appropriate for uniform surfaces and can provide sensitive and accurate measurements of wet film thickness compared to notched gauges.

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