Ceramic tile & polyurethane
No, you can't. You need to buy a tile SEALER that, specifically, designed for this purpose. FIrst, you need to clean the tiles. Check into Muratic Acid. READ THE DIRECTIONS CAREFULLY! I'm not sure if it's to be used for this purpose, but the bottom line is you need to clean the tile before you seal it.
My best to ya and hope this helps.
Jay J -Moderator
PS: God Bless America!