Effect of wollastonite extender on the properties of exterior acrylic paints

•Water based paints with calcite and/or wollastonite extenders were prepared.•Acicular wollastonite enhanced water vapor transmission (WVT) of paint films.•High PVC, semi-transparent paints had better WVT than opaque, low PVC paints.•The hiding power of some wollastonite based paints advanced from class 3 to 2.•Use of Wollastonite hindered mold growth and did not affect weathering properties.

Performance of an exterior paint film is seriously affected by its water permeability and water vapor transmission property. Commercial acrylic binders provide adequate protection for the former, but cannot accomplish top level, for the latter. In the present work, the effects of substitution of irregular shaped calcite extenders with acicular shaped wollastonite with two different particle sizes were investigated on opaque and semi-transparent acrylic paints, having high and low PVC values. A profound increase, up to 85% on water vapor transmission of coatings was observed, especially for high PVC samples, along with improvement of hiding power. Results of painted panels exposed to weathering tests, which were followed for 42 months, indicated no loss in weathering properties, but significant mold growth inhibition was obtained in the case of substituting calcite with wollastonite extender.