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How To Fix Small Toilet Tank Cracks

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If you notice a leak around your toilet, check the toilet tank for cracks. Cracks in toilet tanks may be present at the time of manufacturing, or they could be caused by extreme heat or cold. Cracks have the potential to cause serious water damage. Here are some tips to fix a cracked toilet tank.

Prepare to Work

For this project, you need:

  • work gloves
  • adjustable crescent wrench
  • several sponges, towels, and chamois cloths
  • liquid soap
  • putty knife or popsicle stick
  • caulking gun
  • packing tape (optional)
  • water proof epoxy
  • ceramic finishing spray 
  • caulking gun
  • hair dryer

Inspect inside and outside of the toilet tank for cracks. The size and location of the cracks determines if the toilet tank needs to be replaced. Cracks less than 1/16 wide can be fixed.

Cracks that are more than 1/16 inches wide running from the inside to outside of the tank usually indicates the toilet bowl needs replacing. A crack on the top of the tank or on the top edge of the tank usually is a cosmetic problem.

Turn Off Water

Turn off the water supply to the toilet, even if it isn't leaking. The toilet water shut off valve is commonly located beside the toilet near the wall. If you can't find the valve, turn off the main water supply to the house, which is near the water meter.

Remove the lid, and lay it in a safe place. Flush the toilet, and absorb extra water with towels, sponges, or chamois cloths.

Clean the outside of the toilet tank to remove condensation, then let the toilet dry with the lid off, so the epoxy can seal properly. Set a hair dryer on the highest setting to speed up drying.

Apply the Epoxy

Clean the repair area with soap and a sponge or cloth, then it let dry. Snip the tip of the epoxy tube, and place the tube inside the caulking gun. Begin applying epoxy around one inch before the crack, and continue applying the epoxy until it reaches one inch beyond the crack on the opposite end.

Use the putty knife or popsicle stick to spread the epoxy over the tank glazing; being careful not to widen the crack. Don't remove extra epoxy. If the crack is vertical, cover it with packing tape to prevent dripping.

Allow the epoxy to dry according to manufacturer's instructions. Watch the tank for glazing cracks during the drying period. Apply a ceramic finishing spray after the epoxy dries for a glossy finish.

Turn the water back on, and watch for leaks. If the toilet still leaks, or the cracks are large, contact a plumber to install a new toilet tank.


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