Sealing During Installation
Frameless glass shower doors use jambs with tight U-shaped borders that are designed to lock onto the base of the shower. If you have a frameless glass shower door, buy jambs that create watertight seals with these borders. The best kind of jambs are plastic, polycarbonate or vinyl that are rated for watertight seals. Make sure the plastic and the borders of the shower are very clean and dry before putting these frameless door jambs in, because only small amounts of dust or water can compromise this pressure-based seal.
Framed shower doors are screwed into place in the shower base. If you use tile, make sure you notch the tile before drilling it and use anchors to hold the screws properly. If these screws fail, your frames will become loose, allowing water to leak out onto the bathroom floor. When installing the doors themselves, look for rubber or plastic strips known as shower door "thresholds." Seal the strips to outline the door so that when they close they can keep water out more effectively.
Sealing After Installation is Complete
Once the frames are in place, you will need to seal them with caulk. You'll need caulk that is waterproof and durable. Look for a good silicone caulk that is used for showers and apply it carefully when the frame and the shower are completely dry. Make sure the silicone caulk is no older than six months so that it will cure properly.
Silicone caulk will create a seal in the shower with enough flexibility so that the caulk will not crack and let water seep into the frame. Once the caulk is cured, you will need to keep it clean to make sure mildew and mold will not develop. Some types of silicone caulks come with moldicides imbedded in the caulk to keep unwanted spores from growing once you start using the shower.