Can I add MAPEI / Keraply Mortar Latex additive to sanded grout to a glass mosaic piece for outdoor use? Does it matter if I use that product or an acrylic admix? I obviously need strength, durability, and most of all mildew and mold resistance. What is the difference between the two...

Can I add MAPEI / Keraply Mortar Latex additive to sanded grout to a mosaic piece for outdoor use? Does it matter if I use that product or an acrylic admix? Thanks!