Ressi TG 820 Ressi TG 820 is a colorfast cementitious grouting for use as a joint filler for most types of ceramic tiles and natural stone applications. Ressi TG 820 is water resistant and can be used for both internal and external application. Ressi TG 820 is an ideal grout to be used for its application in bathrooms and swimming pools. Ressi TG 820 is specially designed for areas where there is reasonable presence of moisture and special protection against mold, fungus and bacterial is required.