It is important to seal terracotta tiles and clean them regularly to extend the life of your floor and protect its appearance. Existing floors are probably already sealed, but new floors should be sealed right after they are laid. Terracotta tiles can be sealed with any commercial stone sealant (some sealants are specifically meant for terracotta, which is also fine). Once your tiles are properly sealed, regularly cleaning them with mild soap and water will protect the seal and enhance the look of your floor.
Wash your tiles thoroughly to remove any dirt or sand before applying sealant. If possible, use a wet vacuum intended for hard floors. Rinse the floors with water to remove any soap residue left from the vacuuming, and allow them to dry completely.
Pre-seal your tiles before you add grout if you are installing new terracotta tiles. Use a stone sealant intended for pre-sealing (look for a sealant that specifically says it can be applied within 24 hours of laying the tile, or that it is intended for pre-sealing). Read the application instructions on your sealant before you begin, and be sure to use a clean cloth or paint brush for application. Once the pre-sealant has dried according to the manufacturer's instructions you can apply your grout.
Seal new tile floors after grouting, or reseal old floors when the seal is worn out. Properly sealed floors will have a smooth, shiny appearance. Unsealed floors or floors with a worn seal, will be dull, and the porous surface of the tile will be visible. As long as the old seal is not peeling or bubbling, you can reapply new sealant over top of the old seal. Use a clean cloth or brush to apply a thick coat of stone sealer over clean floors. Start in one corner of the room and work your way backward toward a doorway, so you are not kneeling or walking on freshly sealed tiles.
Allow the seal to dry completely according to the manufacturer's instructions before walking on your tile floor.
Clean your floor frequently with water and mild soap to maintain its appearance. Dirt and sand will wear away the seal on your tiles, so the more frequently you clean your floor the less often you will need to apply sealant. Wash the floor with a mop or rag to remove everyday dirt, and use a plastic brush to clean larger messes.
Be sure to ventilate the room when applying sealer; the fumes can be dangerous if there is not enough airflow. Choose water-based sealants over wax-based sealants to avoid the residue that wax can leave on a terracotta surface. You may need to apply several coats of water-based sealant before the floor is fully sealed. Follow the manufacturer's instructions for proper application.