5 Litre Crown Trade Alkaline ( Px4 ) PrimerCrown Trade PX4 is a rapid drying, adhesion promoting primer for interior & exterior use. Ideal for difficult substrates including glass, ceramic tiles, melamine and previously painted surfaces, as well as most wood and non ferrous metals. It also has excellent stain sealing properties and can be used on most surfaces subject to staining by smoke, crayon, tannin, water stains and aerosol etc. Stains are held in the primer and will be obliterated by