Polyurethanes don't always stick well to everything. The coating on the terra cotta should be sanded with fine sandpaper then coated with the urethane in a small test area 1st. Next day rub down some packing tape & try to pull it off. If the coating comes off with the tape you have an adhesion problem. If it sticks you can do the whole thing, but be aware it will scratch & cut with knifeblades on countertops, like on floors. BonaKemi's Traffic or Mega are good low gloss choices.