I have a lot of rental property and just finished adding tile to several units. My construction manager, who has done a lot of really good jobs for me, explained that he would not use the sealant that is sold at Home Depot or any of the "consumer" type stores; he said those kinds did not seal the tile properly and he insisted on buying the sealant from a store where he buys tile. He pointed out some properties that a maintenance man sealed for me with the "consumer" type sealant and the grout was already starting to come off. So maybe the tile was sealed but it was not sealed with the right kind of product. Re-doing it with something you buy at a consumer store may not be much better; I would do some research and see where the real tile guys buy their supplies. good luck.