Methods for improving surface roughness of an environmental barrier coating. The methods include providing a component having a plasma sprayed environmental barrier coating, applying an outer layer repair slurry to the environmental barrier coating of the component, drying the environmental barrier coating having the applied outer layer repair slurry, and sintering the component to produce a component having an improved surface roughness. The outer layer repair slurry includes water, a primary outer material of BSAS, and a slurry sintering aid selected from rare earth nitrate, rare earth acetate, rare earth chloride, rare earth oxide, ammonium phosphate, phosphoric acid, polyvinyl phosphonic acid, and combinations thereof.