Yes. If the paint is well bound and not flaking, peeling, bubbling etc. The recommended key coat is Unitex Polymer Render as it is a render designed to adhere to difficult substrates such as strongly adhering paint. As always, ensure the surface is dry, clean and free of oils, dust, dirt etc before applying. Test with a sharp knife, using the “Cross-hatch Method” (see Unitex.)  If greater than 15% pull off and remove all loose and poorly adhering paint prior to coating.