Toilets and other bathroom fixtures are commonly made of porcelain, which is formed of clay and other materials. This mixture is then fired at high temperature in a kiln and glazed to create the porcelain used in bathrooms. Although porcelain is a hard substance, it is not immune to chips or cracks. Sansone notes that some cracks are caused by impacts from something falling and hitting the toilet; other cracks may simply form as a function of a toilet's age.
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You can repair some porcelain toilet cracks, particularly those that form a well-defined line. But cracks that are "spidery" looking, with secondary cracks splintering off a primary crack, may indicate you need to replace the toilet. If you attempt to repair a porcelain toilet crack, exercise caution and go slowly as you work. The main danger to be aware of is to keep the crack from spreading while you work.
How to Repair a Porcelain Toilet Crack
Step 1: Locate the Crack
Identify the crack that you want to repair. If it is on a part of the toilet, such as the tank, that is below a water line, the water in the toilet should be drained before proceeding.
Step 2: Shut Off the Water Supply
Shut off the water for the toilet. Follow the water line connected to the bottom of the tank to the water supply valve. Rotate the knob to shut off the water.
Step 3: Flush the Tank
Flush the tank. Keep pressure on the handle and allow all the water to run out. Remove the tank lid.
Step 4: Clean the Cracked Area
Clean off the area around the crack with bathroom cleaner and a lint-free cloth.
Step 5: Drill Through the Porcelain
Attach the diamond rotary grinder bit to the rotary tool. Identify the end of the crack that is the widest. Drill a hole all the way through the porcelain surface. Spray the rotary tool bit with water periodically to keep it lubricated while drilling. This hole will relieve the pressure on the crack and keep it from getting larger.
Step 6: Widen the Crack
Follow along the crack with the rotary drill bit. Bathroom Machineries recommends cutting a channel that's 1/8 inch wide and and 1/8 inch deep along the crack to give the epoxy more surface on which to bond. Continue spraying with the water as you work.
Step 7: Fill the Crack With Epoxy
Fill the crack with epoxy paste. Depending on your epoxy, it will either come premixed or you will have to follow the manufacturer's instructions to mix it during the repair. Apply the paste into the channel that you drilled. The final level of the epoxy should be slightly above the surface of the porcelain. Allow the epoxy time to cure according to instructions.
Step 8: Sand the Cured Epoxy
Sand down the epoxy with 40-grit sandpaper. Gradually move to finer-grit sandpapers as the epoxy begins to become level with the surface of the porcelain.
Step 9: Apply Resurface Finish
Apply resurfacing finish to the epoxy. Allow this to dry and coat again as needed.
Repairing a crack in a porcelain toilet is a temporary fix. The cracked piece needs to be replaced as soon as possible.