30 mils is a rather big crack and borderline for most elastomeric coatings. All elastomeric coatings I have used suggest patching cracks larger than 1/32 of an inch. 1/32 inch=31.25 mils.
Use an appropriate and manufacture recommended patching compound for cracks of this size and larger. Very tight non-structural hairline cracks can be pre-filled before applying the first coat.