Hi Sean & Steve we used a similar Rust Oleum product and was told for preparation ,(just remove all loose material ,wash floor with their cleaner ).Cost about £ 500.00 for 1000 square feet,three years later most of it gone !
My advice is remove all previous coatings and then acid etch the floor.
We applied the coating with 18 " floor rollers coating has about 45 minutes working time once the activator is added.
Looked really good for about 6 months then one tiny lifted add then it started lift all over the workshop.We called the rep out and he said the exiting coating wasn't "adhered to the sub base " and the epoxy was pulling that off .
They have since amended their preparation instructions .fat lot of good it did us !