Guide
Repair a cracked toilet tank
Use 2-part epoxy on a short, clean crack you can dry and reach from the outside. Silicone will not hold a tank full of water. If the tank is in pieces, the crack runs through a bolt hole, or it still weeps after a cure, replace the tank.
This task involves: Water immersion
Best Glue for This Repair
Fills a clean ceramic crack and stays waterproof once cured — the only household adhesive that can hold a still tank wall.
Reviewed and adjusted by an editor.
Why 2-part epoxy Works Here
- A clean break fits back like a puzzle with almost no gap — ideal for thin glue lines. Unglazed faces are porous; glazed faces are not.
- Fills the tiny gaps in a clean break and survives hot water.
How to do it
Repair a cracked toilet tank: Step by Step
Shut the water off first
- Close the supply, flush, and hold the handle down until the tank is empty. Sponge it dry. If the tank has come apart, or the crack runs through a bolt hole, stop and replace it.
- Dry the crack from the outside. Wipe glaze with rubbing alcohol and let it flash. The epoxy has to sit on dry ceramic.
- Mix 2-part epoxy and work a thin coat into the crack from the outside, slightly proud of the glaze. Do not try to fill the tank from the inside.
- Leave the tank empty until the epoxy has fully cured. Do not refill early — standing water on a soft patch lifts it.
- Refill and watch the crack. A new weep means the tank is finished. Replace it. Do not keep patching a tank that still leaks.
Conditions
When to Use a Different Glue
Epoxy is a patch on a still crack. A crack that opens when the tank fills, or that runs from a bolt to the rim, is the porcelain telling you it is done. Shut the supply off before you start. Do not flush a leaking tank onto the floor.
Avoid
Glues to Avoid for This Repair
Avoid
Bathroom silicone
It skins over a weep and then peels. It seals a joint; it does not put a cracked tank back together.
Avoid
Super glue
It is brittle and it softens in standing water. A tank full of water will pop it off.
Questions
Common Questions About This Repair
- Can I just silicone a cracked toilet tank?
- No. Silicone skins over a weep and then peels. It cannot put a tank wall back together under a column of water. Use 2-part epoxy on a short, still, dry crack, or replace the tank.
- Can I use the toilet the same day I repair the tank?
- No. The tank has to stay empty until the epoxy has fully cured. Water on a soft patch lifts it, and the floor gets the spill you were trying to stop.
- When should I replace a cracked toilet tank instead of gluing it?
- Replace it if the tank is in pieces, the crack runs through a bolt hole, it opens when the tank fills, or it still weeps after a full cure. Those cracks will not stay shut.
- Should I epoxy the crack from inside the tank?
- No. Work from the dry outside. The inside stays wet longer, and you cannot keep the patch still under filling water. A thin outside coat on dry glaze is the repair.