How to regrout a shower

What you need

• Grout removal tool or oscillating multi-tool with grout blade
• Sanded grout (walls and floors) in a colour close to the original
• Grout float, bucket, sponges, microfibre cloth
• Silicone remover and neutral-cure silicone for the corners
• Safety glasses and a P2 respirator — grout dust is silica, and a nuisance dust mask is not a control for it. Better again, hold a vacuum nozzle at the blade or use a manual grout saw

Step by step

1. Test whether regrouting is the right fix

   Push firmly on a few tiles. If any move, sound hollow, or the wall flexes, stop. That is a bedding or waterproofing failure and new grout will crack again within months. Regrouting only works when the tiles are solid and the grout is simply worn, stained or crumbling.

2. Remove the old grout to at least 3mm depth

   Work the removal tool along each joint, keeping the blade centred so you do not chip the tile edges. Do the vertical joints first, then horizontal. You want a clean channel, not a skim — new grout laid over old will sit proud and pop out.

3. Vacuum and wash the joints

   Every trace of dust has to go or the new grout will not bond. Vacuum the joints, wipe with a damp sponge, then let the whole area dry completely. Rushing this step is the single most common reason DIY regrouting fails.

4. Mix and apply the grout

   Mix to a smooth peanut-butter consistency and let it slake for the time on the bag. Hold the float at 45 degrees and press the grout hard into the joints diagonally across the tiles. Work in sections of about one square metre — grout goes off faster than you expect.

5. Clean off the haze in stages

   Wait 15–20 minutes, then wipe diagonally with a barely damp sponge, rinsing constantly. Come back an hour later for the fine haze with a dry microfibre. Too much water at this stage washes cement out of the joint and leaves it weak and patchy.

6. Silicone the corners, not grout

   Every internal corner — wall to wall, wall to floor, around the bath — must be flexible silicone, never grout. These are movement joints. Grout in a corner will crack, every time. Let the grout cure fully first, then cut the old silicone out and run a fresh neutral-cure bead.

First: is regrouting even the right job?

Grout is porous by design. It is not, and has never been, what keeps water out of your shower — the waterproof membrane under the tiles does that. So grout that is stained, patchy or crumbling in a few spots is a cosmetic and hygiene problem, and regrouting fixes it.

Stop and reconsider if you see any of these:

• A white, chalky bloom in the grout lines that keeps coming back after you clean it — that is efflorescence, mineral salts being carried out of the bed by water that should not be in there
• Tiles that sound hollow when you tap them with a knuckle
• Grout that stays visibly darker than the rest a full day after the shower was used
• Bubbling paint, swollen skirting or a musty smell on the other side of that wall
• A stain on the ceiling below an upstairs bathroom

Any of those and you are looking at a waterproofing failure, not a grout problem. New grout over a failed membrane buys you a nicer-looking shower and no extra time at all — the water is already travelling underneath, and sealing the surface can trap it.

What you are actually removing, and how much

You are taking out the top few millimetres of grout across the joints, not excavating to the tile bed. Aim for roughly two to three millimetres deep — enough for the new grout to key into, not so much that you undercut the tile edges.

The tool decides how the day goes. An oscillating multi-tool with a grout blade is fastest and also the easiest way to chip a tile if you rush a corner. A manual grout saw is slower, much harder to do damage with, and honestly fine for a single shower. If you have never done this, start on the wall joints where the tile edges are less exposed, and get your technique before you go near a visible corner.

Do not run the multi-tool along an internal corner or where the wall meets the floor. Those joints should not have grout in them at all — see the next section.

The corners are meant to be silicone, not grout

This is the single most common mistake in Melbourne bathrooms and it is worth understanding rather than just obeying. Buildings move. Timber-framed houses move seasonally, brick veneer moves, a bathroom floor above a subfloor moves every time someone walks across it.

Grout is rigid and cracks when the surfaces either side of it move relative to each other. So every internal corner — wall to wall, wall to floor, around the shower base, around the hob — is supposed to be a flexible silicone joint that can absorb that movement. If your corners are currently grouted and cracked, that is not a mystery, that is the cause.

When you regrout, rake those corners out and silicone them instead. It is the difference between a regrout that lasts and one that cracks again next winter.

Mixing and working the grout

Buy more than you think — running out mid-wall and mixing a second batch is the most reliable way to end up with two slightly different colours in one shower. For a standard shower enclosure, two kilograms is usually comfortable.

Mix to a stiff peanut-butter consistency, then let it stand for the slaking time on the bag (usually five to ten minutes) and briefly remix. Skipping the slake is why some grout goes powdery and weak weeks later — the additives have not fully wetted.

Work it in diagonally across the joints with the float held at about 45 degrees, in both directions, so the joints are packed rather than skimmed. Do a manageable area — say a square metre — then stop and clean it before moving on. Grout that has gone off on the tile face is a genuinely miserable thing to remove.

Cleaning off, and the haze

Wait until the grout is firm to a fingertip — commonly fifteen to thirty minutes, longer in a cold Melbourne bathroom in July, much shorter in a warm room. Then wipe diagonally with a barely damp sponge, rinsing constantly in clean water. Diagonally, always: wiping along a joint drags the grout back out of it.

A light haze will appear on the tiles as it dries. That is normal. Buff it off with a dry cloth once the grout has hardened, usually a few hours later. Do not attack the haze with more water while the joints are still green — you will wash the surface of the grout out and get a patchy, pale finish.

Curing, sealing, and the bit everyone skips

Keep the shower out of use for at least 24 hours, and longer if the room is cold. This is the step people compromise on and it is the one that determines whether the grout is hard-wearing or crumbly.

After the manufacturer's cure time — often seven days — a penetrating grout sealer makes future cleaning much easier. It is not waterproofing and does not pretend to be. It just slows how fast the grout absorbs soap, shampoo and body oils, which is what actually discolours it.

What it costs, and when to just get it done

Materials for a single shower are modest: grout, a float, a grout saw or multi-tool blade, sponges and a sealer. Call it an afternoon of shopping and most of a weekend of work if it is your first time.

The honest limit: if the tiles are drummy, if the bathroom is more than a couple of decades old and has never been touched, or if you are regrouting because it keeps going mouldy, you are treating a symptom. In an original post-war Melbourne bathroom, regrouting a shower that is failing underneath is money and a weekend spent to delay the real conversation by about a year.

Common mistakes

• Grouting the corners instead of siliconing them
• Not removing enough of the old grout, so the new layer is too thin to hold
• Working with the joints still damp or dusty
• Using too much water when cleaning, which leaves soft, crumbly joints
• Sealing over mould — it grows straight back through

Questions people ask

Can I grout over old grout?

No. New grout needs two to three millimetres of clean depth to key into. Skimmed over the top of existing grout it has nothing to bond to and will powder out within months — usually in the exact spots that were already the worst.

Sanded or unsanded?

Joints wider than about 3mm take sanded grout; narrower joints take unsanded. The other factor is the tile: polished stone and some glass tiles scratch, so unsanded or an epoxy grout is safer there even in a wider joint.

Should I use epoxy grout?

It is far more stain-resistant and much less forgiving to work with — it goes off fast and it does not clean off a tile face easily once it has. For a first regrout in your own bathroom, a good cement-based grout plus a sealer is the more realistic choice.

The grout keeps going mouldy no matter what I do.

Then the problem is probably not the grout. Persistent mould usually means either a ventilation problem or moisture being fed from behind. Check whether the exhaust fan actually moves air, then read the waterproofing guide.

How long does a regrout last?

Done properly, on a sound substrate, with silicone in the corners rather than grout — many years. Done over a failing membrane, months.

This guide is general information, not advice for your particular house. Rules change — check the current position with the Building and Plumbing Commission, Energy Safe Victoria and WorkSafe Victoria before you rely on it. Plumbing, gas and electrical work must be done by a licensed practitioner. If your home was built or last renovated before 1990, assume asbestos until it is ruled out — see what a strip-out finds.