Why does the grout in my shower corner keep cracking?
Shower corners and the tub-to-wall line usually crack when grouted because those joints move slightly; fill them with 100% silicone instead, which flexes. Rake out the old grout or caulk, clean off mildew, let the joint dry, tape both edges, run one steady bead, smooth it, pull the tape, and let it cure 24 hours before showering.
How to do it
- Rake out the old grout or caulkUse a grout saw or utility knife to remove all the old material from the corner or tub joint. Leave clean, sound edges on both sides.
- Clean off mildew and let the joint dry fullyScrub away any mildew, rinse, and leave the joint to dry completely, ideally overnight. Silicone bonds poorly to a damp or mouldy surface.
- Tape both edges of the jointRun painter's tape along the tile side and the tub or wall side, leaving a gap the width of the bead you want.
- Run one steady bead of 100% silicone and smooth itLay one continuous bead along the gap without stopping, then smooth it in a single pass with a smoothing tool or a wet fingertip.
- Pull the tape and let it curePeel the tape off at a low angle while the silicone is still wet. Wait 24 hours, or the time on the label, before showering.
Questions that come up
Can I run silicone straight over the cracked grout?
It is not a good idea. Silicone laid over cracked or crumbling grout usually bonds poorly, peels early, and can trap moisture and mildew underneath. Removing the old grout or caulk first takes longer, but it gives the silicone a clean, dry surface to grip, and the repair holds much longer.
Should the flat tiled areas get silicone too?
No. Joints between tiles on the same flat surface barely move, so grout works well there and holds up better to scrubbing. Silicone belongs where two surfaces meet: wall-to-wall corners, the wall-to-tub or shower-pan line, and similar change-of-plane joints.
What if mildew comes back on the new silicone?
Silicone does not make a shower mildew-proof. If dark spots return quickly, the joint was probably not fully clean or dry, or the bathroom lacks ventilation. A mildew-resistant bathroom silicone, running the fan after showers and wiping the joint dry help. Mildew that has grown under the bead means cutting it out and redoing it.
Is acrylic or siliconized caulk just as good?
Not for a wet shower joint. Acrylic and siliconized acrylic caulks are easier to tool and can be painted, but they usually stay flexible and waterproof for a shorter time under constant water. For the corners and tub line, 100% silicone tends to last longer. Check that the label says 100% silicone.
Full transcript
That cracking shower corner needs silicone, not grout. Rake out old grout or caulk, scrub off mildew, let it dry, then tape both edges. Run one steady bead of 100% silicone and smooth it. Pull the tape. Joints move; rigid grout usually cracks, silicone flexes.