The minimum and maximum permissible values for paint film thickness will be specified in the painting specification. Therefore, effective control of film thickness is required. Wet film thickness (WFT) can be checked immediately after application. Normally, constructors should check this periodically during construction. There are two types of wet Film Thickness Gauges used: comb and roll.
Wet Film Thickness Gauges can be used for almost all coating products, but not for inorganic zinc silicate coatings because their solvents evaporate too quickly. At the same time, for physically drying paints, such as chlorinated rubber paints, the measurement of the second paint is not suitable because it will redissolve the previous paint.
The correct film thickness will be stated in the product data sheet. As long as the dry film thickness (DFT) and the volume solids content (%, VS) are known, the wet film thickness (WFT) can be calculated. At the same time, it is also necessary to consider how much thinner (%, Wthining) is added to calculate the correct wet film thickness.
Comb wet Film Thickness Gauges are usually made of stainless steel or aluminum alloy, or plastic materials, but their service life is not very long. When measuring, place the wet Film Thickness Gauge firmly in the wet film on the surface of the substrate, then take out the Thickness Gauge, and check which of its comb teeth has the shortest contact with the wet film. The thickness of the wet film is between the last comb tooth that touches and does not touch the wet film. Take the thickness indicated by the teeth of the comb in contact with the wet film. At least two or three measurements should be taken to get the most representative reading. Wet Film Thickness Gauges should be cleaned immediately after use.
