There is a latex grout additive that will keep mildew from growing. You never have to seal the grout either. When we were getting our bathroom redone I asked the builder to use that in the shower. He said it was alot more expensive than plain grout. Turns out it cost forty dollars to do the whole shower. Plain grout would have cost four dollars. So thirty six bucks to never see mold or have to seal grout? Priceless!