Fernox LS-X External Leak Sealer is a proven, fast acting, silicone paste which is used as an effective external leak sealer and jointing compound. It is designed for use on hot and cold water services, including potable water. Ideal for use on compression joints and screwed fittings. Never sets rock hard, joints can easily be undone. Ready to use, no mixing required. Does not shrink or crack with age. Suitable for use from below freezing point to above boiling point of water. Completely safe to use with drinking water