Tips – check first if old paint is oil-based enamel first (all water based paints can have issues adhering to oil-based paint without proper preparation).  Oil-based paint will require light sand, wipe down and a coat of Zinsser Smart Prime before applying 2 coats of Econamel.  If old paint is water-based, just a light sand and wipe down plus 2 coats of Econamel.