Grout is porous, and unsealed grout absorbs water every time you shower — sealing it doesn’t make grout waterproof, but it slows that absorption enough to stop the mould, staining, and eventual leaks that untreated grout leads to. Most cement-based grout needs resealing every 12–24 months. This guide covers what sealer actually does, how to tell when yours has failed, and when a grout problem has moved past what sealer can fix.

If your grout looks fine but water is still getting through somewhere, book a leak inspection — sealer won’t fix a problem that’s coming from underneath the tiles, not the surface.

What does grout sealer actually do?

Cement-based grout is essentially a sponge at a microscopic level — full of tiny pores that pull in water. Grout sealer sits in those pores and makes the surface water-repellent, so water beads and runs off instead of soaking in.

What it doesn’t do is make grout waterproof. A sealed shower still relies on the waterproof membrane underneath the tiles to actually stop water getting into the wall or floor structure — the sealer’s job is to protect the grout itself from staining, mould growth, and gradual breakdown, not to be your shower’s primary defence against leaks.

Do you need to seal grout in a shower?

If your grout is cement-based (the vast majority of Australian showers, especially anything not renovated in the last few years), yes. Cement grout without sealer will absorb water, discolour, and become a breeding ground for mould within months.

The exception is epoxy grout, which is non-porous by nature and doesn’t need sealing at all. If you’re not sure which you have, epoxy grout looks glossier and feels slightly rubbery compared to the matte, slightly chalky texture of cement grout.

How often should you reseal grout?

For a shower in regular daily use, every 12–24 months is the standard guide. A few things shift that window:

  • Heavier use (a family bathroom used multiple times a day) wears sealer faster than an occasional-use guest shower.
  • Harsh cleaning products — anything acidic or abrasive — strip sealer faster than a gentle pH-neutral cleaner.
  • Poor ventilation means grout stays wet longer between uses, which accelerates sealer breakdown.

The simplest way to know for sure: the water test below.

The water test — how to tell if your sealer has failed

Splash a small amount of water onto a dry grout line and watch what happens for 30 seconds.

  • Beads up and sits on the surface — sealer’s still working.
  • Soaks in and darkens the grout — sealer’s gone, time to reseal.

This takes literally a minute and is the most reliable DIY check available — more reliable than just going by time elapsed, since usage and cleaning habits vary so much house to house.

Other signs your grout sealer has worn out

  • Grout lines look permanently darker or dirtier than they used to, even right after cleaning
  • Mould keeps coming back in the same spots no matter how often you clean it
  • Grout feels slightly soft or crumbly when you run a fingernail over it
  • Visible white or grey staining that wasn’t there before (mineral deposits from water soaking through)

Sealing grout yourself vs calling a professional

DIY grout sealing is genuinely doable for a competent home renovator — the products are widely available and the process is straightforward: clean the grout thoroughly, let it dry completely (24+ hours in a well-ventilated bathroom), apply sealer with a small brush or applicator, wipe excess off the tile surface, and let it cure before the shower’s used again.

Where it gets harder to DIY well:

  • Grout that’s already compromised — cracked, crumbling, or with gaps — needs repair before sealing does any good, and that shifts into regrouting territory
  • Full drying time is easy to underestimate in a bathroom that doesn’t ventilate well, and sealing over damp grout means it fails early
  • Picking the right sealer for your specific grout colour and type (some sealers darken lighter grout noticeably)

If your grout is in good condition and you’re comfortable with a fiddly, precise job, DIY sealing is a reasonable weekend project. If the grout itself is damaged, regrouting needs to happen first — sealing damaged grout just locks the problem in rather than fixing it.

What happens if you never seal (or reseal) your grout

Unsealed or under-sealed grout doesn’t fail all at once — it’s a slow slide:

  1. Grout absorbs water with every shower
  2. Constant dampness feeds mould growth in the grout lines
  3. Grout gradually weakens and starts to crack or crumble
  4. Once grout has gaps, water reaches the substrate behind the tiles
  5. That’s when you move from a cosmetic grout problem to an actual leaking shower — the kind that can mean pulled-up tiles and floor damage to fix properly

Catching it at the sealer stage is the cheapest possible point to intervene. If you’re already seeing signs of a leak rather than just tired-looking grout, that’s a different problem — get in touch and we’ll tell you honestly whether it’s a sealing job or something more.