Many people like the look of a flagstone floor. This type of stone flooring is attractive and easy to maintain if installed correctly, sealed properly, and grouted the right way. It's also easy to fix since the floor is most commonly installed in the form of tiles or sometimes slabs. Simply remove the damaged section, replace it with a new section, and grout again. It's always a good idea to purchase several extra slabs or tiles with the original order as well as extra grout. This ensures that when a repair to the flagstone floor is required, you don't have to worry about color variations with a new container of grout or a different batch of stone.
Step 1 - Remove the Damaged Piece
With a masonry chisel and hammer, loosen the grout around the damaged flagstone floor tile or slab. Be careful not to damage the surrounding tile. Chisel toward the damaged piece so if the chisel slips it doesn't cause nicks in the other parts of the floor. Take your time. You can also try a hammer drill and carefully drill small holes in the damaged stone to further crack it and make it easier to remove. Remove all pieces then thoroughly vacuum the area to remove any small chips and dust.
Step 2 - Install New Backer Board
Cut a piece of the backer board to fit the area of the floor that has been damaged. If the installation had been done correctly, there should have been a backer board under the flagstone floor to provide a water-resistant layer between the stone and the subfloor. The previous backer board may have been damaged especially if you've removed a large section of stone. Make sure the new piece is correctly sealed. Ideally, try not to damage the backer board during the stone removal.
Step 3 - Position the Replacement Flagstone Flooring
Cut the tile or slab to the correct size if necessary using a tile saw. Make sure you use enough water to keep the cut edges smooth. Depending on the type of flagstone flooring you have, you may need to add mortar to the back of the piece to keep it in place. Put the tile in the correct spot. Push down firmly to make sure there are no air pockets underneath the tiles. Air pockets could cause the replacement to shift or crack. If using mortar, allow the mortar to dry several hours before grouting. You may have to allow it to sit for 24 hours before continuing work.
Step 4 - Apply the Grout
Mix the grout according to the manufacturer's directions. Apply the mix to the joints with a grout float. Use a sponge and clean water to wash excess grout. Clean grout as often as necessary. Allow the grout to dry overnight. Brush on the sealant to protect both the tile and the freshly applied grout. Use a high-quality brush to reduce the chance of any bristles coming loose and getting stuck in the sealant. Allow the sealant to dry for several hours before using the floor.