Why Is Grout Cracking?

Grout cracks for one of three main reasons: movement in the substrate behind the tiles, grout that was mixed or applied incorrectly, or using rigid grout in a joint that needed a flexible one — like the gap between a bath and a tiled wall. Fixing it properly means identifying which of these applies, not just re-grouting over the top.

Common causes

• Movement joints grouted rigidly: the joint where a wall meets a bath, shower tray or another wall should be filled with flexible silicone sealant, not rigid grout — these areas naturally flex slightly with use and temperature changes, and rigid grout will crack there repeatedly no matter how many times you redo it.
• Substrate movement: if the wall or floor behind the tiles isn't rigid enough (a stud wall that flexes, floorboards that deflect underfoot), the tiles and grout above will crack over time. This is a more serious underlying issue that re-grouting alone won't fix.
• Grout mixed too wet or too dry: incorrectly mixed grout is weaker and more prone to cracking and crumbling than properly mixed grout.
• Grout applied too thinly or with gaps: if the joints weren't fully packed when the tiling was done, weak points form that crack under normal use.
• Wrong grout type for the joint width: narrow joints need a different grout formulation to wide ones — using the wrong type can lead to shrinkage cracking as it cures.

How to fix cracking grout

1. Identify the type of joint. If it's a movement joint (bath-to-wall, corner, floor-to-wall), rake it out and replace with a proper flexible bathroom silicone sealant, not grout — see our guide on how long bathroom silicone takes to dry for what to expect once you've re-sealed it.
2. For genuine grout joints, rake out the cracked grout to a consistent depth (roughly two-thirds of the tile thickness) using a grout rake or multitool, being careful not to chip the tile edges.
3. Check the substrate isn't moving. If cracking is widespread or recurring in the same spot after re-grouting, the underlying cause is likely movement in the wall or floor structure, which needs addressing before re-tiling will hold.
4. Re-grout with correctly mixed grout, packing joints fully and wiping away excess before it cures.

Choosing the right grout to prevent it happening again

When re-grouting, it's worth considering whether standard cement-based grout is actually the right choice for the joint. Cement grout is porous, absorbs moisture over time, and is more prone to shrinkage cracking as it cures — especially in wider joints or high-moisture areas like inside a shower enclosure. Epoxy grout costs more and is trickier to apply (it sets faster and needs more careful technique), but it's non-porous, far more resistant to cracking, and doesn't stain or need sealing the way cement grout does. For a shower floor or any joint that sees constant water exposure, the extra cost of epoxy grout is often worth it simply because you won't be redoing the job again in a year or two.

Joint width matters too: cement grout manufacturers specify a maximum recommended width for their product (often around 5-6mm for standard sanded grout), and using it in a wider gap than intended increases the risk of shrinkage cracking as it dries. If your tile spacing is wider than the grout's stated range, a wide-joint or flexible additive grout is the correct choice, not a workaround with standard product. If you're only re-grouting a section rather than the whole room, matching the new grout colour to the old can be tricky, since grout naturally lightens with age and cleaning products — many manufacturers sell colour-matched flexible sealant specifically so a partial re-grout and the surrounding sealant look consistent, worth checking before assuming you'll need to redo the whole room to avoid an obvious colour mismatch.

When it's more than a cosmetic problem

Cracked grout on its own is often cosmetic, but if water gets through the cracks into the wall or floor behind, it can lead to hidden damp and, eventually, more serious problems. If you notice cracking alongside any softness in the wall, discolouration, or a musty smell, it's worth investigating further — see our guide on bathroom tiling costs if a more significant re-tile turns out to be needed.

Common mistakes

• Re-grouting movement joints with grout again instead of switching to flexible sealant — this just guarantees the same crack returns.
• Grouting over cracks without raking them out first — this rarely bonds properly and cracks again quickly.
• Ignoring repeated cracking in the same spot, which usually signals a structural movement issue rather than a grouting mistake.