Toilet cracks usually start from an impact, such as a dropped tank lid or a heavy object, or from stress, such as overtightened bolts or a toilet rocking on an uneven floor. Some are just fine surface lines in the glaze that never leak. Others go through the porcelain and let water seep out a little at a time.
The location matters. A crack in the tank leaks clean water and can spill the full tank if it splits. A crack in the bowl, especially near the base, can let waste water escape onto the floor.
Confirming a crack
Dry and look
Dry the toilet completely and look closely with a flashlight, including under the tank and around the bolt holes at the base.
Rule out sweating
Condensation forms evenly across a cold tank on humid days. A crack leaks from one spot, and the drip line traces back to it.
Mark the waterline
Shut off the supply and mark the tank's water level with a pencil. If it drops over an hour and no water reaches the bowl, the tank itself may be leaking.
Check after flushing
Water appearing at a fine line on the bowl right after a flush points to a crack in the bowl.
Patching versus replacing
Epoxy or sealant patch
- May slow a leak for a short time
- Porcelain flexes and the patch often lets go
- Does not restore the strength of the cracked piece
- Only a stopgap, if anything
Replacement
- Removes the risk of a sudden split
- A matching tank is sometimes available for the same model
- Otherwise the whole toilet is replaced
- A good time to update the seal, bolts, supply line and valve
Common crack types
| Type | Risk | Usual response |
|---|---|---|
| Fine crazing in the glaze | Low if it is not leaking | Watch it; no repair needed if dry |
| Crack in the tank wall | Can split and release the full tank | Shut off and replace the tank or toilet |
| Crack at the bolt holes | Bolts lose grip; tank or bowl may shift | Replace the cracked piece |
| Crack in the bowl near the base | Waste water can leak onto the floor | Stop using it and replace the toilet |
Preventing new cracks
- Set the tank lid down on a towel when working in the tank.
- Never overtighten tank bolts or closet bolts; snug them evenly.
- Fix a rocking toilet promptly so the base is not stressed.
- Avoid pouring boiling water into the bowl.
- Do not stand on the toilet or rest heavy objects on the tank.
Questions to ask
- Is the crack through the porcelain or only in the glaze?
- Is a matching tank available, or does the whole toilet need replacing?
- Was there any water damage to the floor?
- What caused the crack, and could it happen to the new toilet?
Common questions
Can a cracked tank break suddenly?
It can. A crack that goes through the porcelain can split under the weight and pressure of the water, which is why it should be shut off.
Are hairline lines always cracks?
No. Fine crazing in the glaze is common and harmless if no water seeps through. Watch it for any dampness.
Can I replace just the tank?
Sometimes, if a matching tank for the same model is available. Otherwise replacing the whole toilet is usually simpler.
General information for Fullerton, not a quote or professional advice. In an emergency, call 911.