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How to Measure Coasting Dry Film Thickness

“How can I measure my coating dry film thickness?”

It is important to apply coatings within the coating manufacturers recommended Dry Film Thickness (DFT). Too little DFT and the coating may fall short of providing the proper protection, whereas too much DFT may cause mud cracking in the film, or unnecessary use of costly coating materials.

There are two ways to check dry film thickness. The first is by using a measurement instrument, and the second by compiling the wet film thickness and doing a simple math calculation. Dry film thickness instrument technologies range from: comparative, magnetic, or electronic. The mechanical comparative is for non ferrous substrates. The magnetic instrument is for ferrous substrates, and the electronic for both substrates with the best accuracy. These test instruments range in price from $80.00 to over $1,000.00 with the preferred instruments in excess of $900.00.  Usually these DFT instruments are used by technicians on the finishing line and the instrument cost is justifiable.

The alternative way to determine DFT is by measuring your wet film and calculating your DFT knowing your coatings percent solids by volume, which is available on the coating manufacturers Product Data Sheet (PDS). Sometimes a percent solids by weight is listed on the PDS and using this percentage will not provide an accurate DFT. 

 The calculation is:  Wet film measured in mils (.001) x percent solids by volume = DFT.

                Example: 5 mils wet x 35% solids by volume = 1.75 mils DFT. 

Measuring wet film thickness is simply done with a wet film gauge such as the one shown in this picture.

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