Your concrete floor should be in good condition and should not contain any loose, chipped (spalled), or cracked areas. For best results, remove all loose material and dust and repair damaged areas before you coat the concrete. If applying to newly poured concrete, allow surface to cure for at least 28 days prior to coating.

A visual assessment of the condition of the floor, as well as checking for moisture and presence of a sealer, are necessary to determine if a floor is in good enough condition to coat.

We do not recommend coating over damaged or marred concrete. Concrete must be sound. If concrete is dirty or greasy, use a scrub brush and degreaser to clean the floor prior to coating, and remove all loose material and dust and repair damaged areas before you coat. The cleaning portion of this answer could be a separate question: How do I clean my concrete before applying a coating?

No, concrete coatings will not fill voids and cracks in the surface. Any cracks or voids should be repaired prior to coating.

Expansion joints are not meant to be coated over. Instead, use a flexible expansion joint caulk for this application.