A description is given of modifications to a dynamic mechanical analyser (DMA) to allow controlled relative humidity (RH) experiments to be performed under isothermal or thermal scanning conditions. Free film samples of polyester melamine paints
(under-cured, normal-cured and over-cured) were supplied and the viscoelastic properties measured in the tensile mode of the
DMA. A reduction in the glass transition temperature (Tg) of up to 10C was found as the controlled RH was increased.