Instant Ocean HoldFast is for bonding to glass or other smooth surfaces. Use it to bond live rock, slate, plants and coral. This is an easy to use product that is safe for all fish and invertebrates and can be used in for freshwater or marine aquariums. Simply clean and rough surfaces to be bonded, cut or break off the desired amount of HoldFast, and knead the mass with your fingers until it turns white. Then apply to bonding surface, being careful to fill any cracks and crevices. Smooth or sculpt any excess HoldFast to blend with surfaces.