If you notice a leak around the base of your bathroom faucet, a few different problems can be the cause. Several parts inside a faucet, including the packing material and the rubber washer, have a tendency to wear out or break down over the life of a faucet. When that happens, they can cause water to leak out around the base of the faucet. You can repair a bathroom faucet that leaks at the base by dismantling the faucet and replacing these worn out parts.
Turn off the water supply for the bathroom faucet that leaks at the base. Look underneath where the faucet is installed for the water supply valves. Rotate the knobs on the end of the valves clockwise until they stop.
Open the faucets and allow any water inside to run out.
Remove the faucet handle. How this is done depends on the faucet model. Some faucets will be held in place by an Allen screw on the underside of the handle. Other faucets, mostly older ones, will be held in place by a Phillips screw concealed underneath the faucet temperature indicator. Pry this cap off in order to remove the faucet handle screw. Pull the faucet straight off the stem.
Unscrew the packing nut. This is the first nut located at the top of the faucet stem. Pull this off the faucet. Unscrew the valve stem by rotating the hexagonal nut located just directly above the faucet body. Pull the stem out of the faucet.
Check the rubber faucet washer at the base of the stem. Replace a broken or worn washer by removing the retaining nut, pulling out the old washer, replacing it with a new one and securing with the nut.
Waterproof the valve stem threads by smearing them with pipe thread compound. Insert the stem back into the faucet body and tighten.
Replace the packing material. The packing material takes the shape of a plastic or rubber o-ring located in the space beneath the packing nut. Remove the packing material with a pair of needle-nose pliers or small screwdriver. Replace with new packing material. Slip the packing nut over the end of the faucet and tighten.
Replace the faucet handle. Secure with the screw.
Insert the silicone caulk into the caulk gun. Trim off the end at the 1/8 inch mark at a 45-degree angle. Caulk around the base of the faucet.