More on Spread Rates and Film Thickness

The relationship between spread rate - given in square metres per litre - and wet film thickness is fixed. Applying paint at a spread rate of 10 square metres per litre gives a wet film thickness of 100 microns. This obviously assumes that the paint is evenly applied to a smooth surface. To calculate the wet film thickness from the spread rate simply divide 1000 by the spread rate. So a spread rate of 8 square metres per litre gives a wet film thickness of 125 microns.
When paint dries, water or solvent (depending on whether the paint applied is water-based or solvent-based) evaporates leaving a dry paint film. The relationship between wet film thickness and dry film thickness is not fixed and will be dealt with in the next post.