Why is it Important to Measure Wet Film Thickness?
A wet film is the coating on a surface which has not yet dried or cured. The coating can be one of many things, icing, chocolate, oil, varnish, but in our field, most commonly; paint. We will consider the coating we discuss throughout this section to be paint. Firstly, we will look at what components go into making paint. These can be split into two; volatile and non-volatile substances.
Volatile Component: the part of the paint which evaporates during the curing process. Known as the “carrier”, “solvent”, “vehicle” or “liquid”, the volatile component provides the correct consistency to enable the pigment and binder to be applied to a surface.
Non-Volatile Component: the paint that remains after the curing process. Non-volatile components can be split into two;
1. Pigments – fine particles that provide the “colour” and typically include titanium dioxide (TiO2) for white and other colouring pigments as required.
2. Binder - the main body of the paint which holds it together and carries the pigment.
Paint can be applied to a surface using several methods such as a brush, a roller, spray and dipping or immersion. Therefore, the volatile and non-volatile components vary in viscosity.
The ability to measure the wet film thickness is important for financial, logistical and quality reasons.
The predicted dry film thickness can be calculated from the wet film thickness using a formula.
Wet film thickness can be measured using a wet film comb, a wet film wheel or a Pfund gauge.