The caulk around the base of your toilet can become grimy, flaked and mildew-ridden with age, at which point it is no longer doing its job of protecting the joint from water damage. The hardest part of replacing it is removing the old caulk (silicone/sealant/silicone sealant/glass silicone), but don't cut corners on the job -- new caulk might not adhere properly to the surfaces if any traces of the old caulk remain. If you take the time to remove the failing caulk properly, the new line can last for years.
Apply a commercial caulk remover to the old caulk if it is hard to the touch and the surfaces surrounding it aren't plastic. The caulk remover softens the caulk and makes it easier to remove, but it damages plastic, so use it cautiously. Read the directions on the label to determine how long to let it work before continuing.
Slice the old caulk off the surfaces with a razor blade. Make a vertical cut along the contours of the toilet base and a horizontal cut along the floor to free the line of caulk. Pull out as much of the caulk as possible with a pair of needle-nosed pliers. Use the hook end of a 5-in-1 painter's tool to pull out remaining slivers.
Scrub the empty joint between the toilet and the floor with a dry, nonabrasive pad to remove lingering traces of caulk. To remove silicone caulk traces, dip the pad in mineral spirits. Open the windows for ventilation and don't introduce any flames into the room while working with mineral spirits. Wipe the surfaces with a damp cloth, and then dry them with a dry cloth.
Spray an anti-mildew cleaner onto the empty joint to kill any mildew that may have been growing under the caulk. Wipe it off with a dry or wet cloth according to the manufacturer's instructions.
Apply a line of painter's tape to the base of the toilet to mark the top border of the new caulk line. Apply a second line of tape to the floor, marking the bottom border of the caulk line. The gap between the two lines of tape should be about 3/8 inch wide.
Trim off the tip of the caulk tube with the razor blade. Cut on a 45-degree angle, and make the opening in the tube about 3/16 inch wide. Fit the tube of caulk into a caulk gun, with the tip of the tube facing away from the trigger.
Place the nozzle of the caulk tube into the joint between the two lines of tape. Hold the gun at a 45-degree angle so the opening in the nozzle lines up with the joint. Squeeze the trigger gently, and smoothly apply a line of caulk between the two lines of tape. Keep the pressure steady, and make sure the caulk emerges from the tube at the same pace as you are moving the gun around the toilet. This keeps the caulk line even and solid.
Wrap a damp paper towel around the tip of your index finger. Press your finger lightly into the line of caulk, and run it all around the base of the toilet to smooth the caulk with the paper towel.
Peel off each line of tape slowly and carefully. Run over the caulk again with the damp paper towel to make sure the line is smooth and even. Allow the caulk to cure for 24 hours or the length of time specified by the manufacturer before cleaning the floor around the base of the toilet.
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