ZINSSER Mould Stop Primer is a water-based coating that can be used to paint over existing stains left by mould, mildew, moss, fungi, and any other fungal organisms. The Mould Stop Primer contains an mildewcide to prevent the growth of mould, mildew, and other fungal organisms on the paint film. The Mould Stop Primer also aides in covering residual microbiological and fungal stains.