Dulux 1Step® Prep Water Based Primer, Sealer & Undercoat is your first step toward a superior long-lasting paint finish. With mould resistance and stain blocking of tannin and flash rust, 1Step® Prep ensures your interior or exterior paint shines now and into the future. Use 1Step® Prep for all general paint surfaces in your home including interior and exterior walls, ceilings, doors, windows, trim, and especially in kitchens, bathrooms and outside areas where mould could be a problem.