We are regrouting vintage porcelain pool waterline tile. Our existing grout is sanded Portland cement white and has held up remarkably well given its age. What is the best sanded grout for a submerged application like a pool. Looking for one that preferably that has or can have additive that makes it waterproof and doesn't require sealing. Not interested in epoxy grout as our pool manufacturer installer advised us just to use sanded cement based grout.