PLGN 2.05 Dry film thickness

(a)
The service life of a conventional coating in a severe environment is likely to be significantly shorter than in a moderate environment. Where it is not possible to modify the environment, or where maximum durability is required, then a higher specification is required. Generally there is a direct relationship between the durability of a coating and it's dry film thickness (DFT).

To convert DFT to WFT (wet film thickness) use the following equation

For example the calculation for Dulux Trade High Gloss would be as follows

(b)
In many circumstances the DFT/Appearance/Coverage is challenged by the Client and demands are made to check that the correct amount of coatings has been applied.

The calculation for a Dry film thickness is :
Film Thickness in microns = (1000/Spreading rate)x Volume solids ) divided by 100

If the spreading rate is 17 m2 per litre (for example Dulux Trade Matt Matt PBW) (Volume solids = 32.47) Film Thickness in microns = (1000/17) x 32.47)/ 100 =(58.8 x 32.47)/100 = 19 microns dry film thickness per coat.

So, for 3 coats of paint we would expect a DFT, at maximum spreading rate, to be 57 microns

A Competitors' product only had a DFT (3 coats) of 48 microns.

As far as we are aware, apart from Ferrous Metal, there is no guaranteed method for measuring Dry Film Thickness on site. We would therefore ask for a sample to be sent to Slough for analysis using either a light microscope, or an electron microscope.