How to Re-Grout a Tiled Floor or Wall

By Steve — flooring and wet-areas, Adelaide Hills.

Regrouting is the job that separates the patient from the impatient. New grout in clean joints is a 6-hour job that lasts 15 years. New grout slapped on top of crumbling old grout is a 6-month job that the homeowner will be back to redoing — except now there’s two layers of old grout to remove and the joints are even worse.

The whole game is removing the old grout properly. That’s 80% of the time and 100% of the difference between an amateur and a pro result. Bunnings sells “grout saws” — handheld hand-tools with a carbide blade. They work, slowly, and they wreck the surrounding tile glaze if you slip. The tool that actually makes regrouting tolerable is an oscillating multi-tool with a grout-removal blade. A $200 multi-tool with a $20 blade does in 10 minutes what a grout saw does in an hour. If you don’t own a multi-tool, hire one for the day from Bunnings or Kennards.

The Aussie wet-area gotcha: AS 3958 specifies that grout in joints over 3 mm wide in wet areas (bathrooms, laundries, kitchens with splashbacks) must be sanded. US “non-sanded” grouts — sometimes the only option in a Bunnings clearance bin — fail under shower water and void any waterproofing warranty on the substrate. For Aussie wet areas, Davco SureColour Sanded or Mapei Ultracolor Plus Sanded are the standards. Don’t drift off this.

What you’ll need

• Oscillating multi-tool (Bosch PMF, Makita TM3010C, Ryobi One+ R18MT or Ozito MTK)
• Grout removal blade — Bosch ATZ 52 or Diablo carbide grout blade ($20-30)
• Vacuum cleaner with brush attachment
• New grout — Davco SureColour or Mapei Ultracolor Plus, sanded for joints over 3 mm
• Grout float (rubber)
• Two buckets — one clean water, one rinse
• Large grout sponge (the $8 yellow-and-white ones at Bunnings)
• Microfibre cloths
• Masking tape
• Knee pads (you’ll need them)
• P2 dust mask, safety glasses
• Silicone for corners (Selleys Wet Area or Sika Sanisil)

Step 1: Identify what you’re grouting and where

Floor or wall? Kitchen splashback or shower? The grout choice depends on the spot:

• Floor with joints under 3 mm: non-sanded acceptable, but sanded preferred.
• Floor or wall with joints 3 mm or wider: sanded grout required (AS 3958).
• Internal corners (wall-to-wall, wall-to-floor, around bath/shower base): silicone, NEVER grout. Grout in corners cracks within months due to building movement.
• Around bath rim: silicone-only. Movement joint.

If the existing job has grout in the corners, plan to silicone those instead.

Step 2: Tape off adjacent surfaces

Mask off the bath, vanity, skirting, anything you don’t want grouted on or scratched by the multi-tool. The multi-tool blade will skip if you sneeze, and grout removal dust gets everywhere. Drop sheet on the floor.

Step 3: Set up the multi-tool with the grout blade

Fit the grout-removal blade. These look like a flat carbide-grit-coated triangle on most tool brands, or a slim circular blade on a few. Set the depth — most multi-tool blades have a depth gauge or you set it by feel. You want to remove grout to about half the joint depth, NOT all the way down to the substrate.

Going too deep risks hitting the tile edge underneath, the waterproofing membrane, or (in older bathrooms) the cement bed below the tile. Half-depth gives the new grout enough joint to bond into without compromising the existing waterproofing.

Step 4: Cut down the centre of every joint, slowly

Run the blade down the centre of the joint, parallel to the tile edges. Light pressure, let the oscillation do the work. The grout will turn to powder and the blade will sink to the depth stop.

Keep the blade dead-centre. If it kicks toward a tile edge, the carbide grit will scratch the glaze — and porcelain glaze doesn’t repair, you live with it. Slow is fast on this step.

Do every horizontal joint first, then every vertical joint. Floor-tile patterns sometimes have grout going both directions and you need to follow the joint pattern.

Step 5: Vacuum every joint thoroughly

Once you’ve cut down every joint, vacuum the powder out with the brush attachment. Then vacuum a second time. Then a damp cloth wipe. Then a third vacuum. Old grout dust mixed into new grout = colour variation, weak bond, and a result that looks streaky.

If any joint still has chunks of old grout in it, go back to the multi-tool and finish removing them. Don’t compromise here.

Step 6: Mix the new grout to the right consistency

Mix small batches — 500 g at a time. Sanded grout sets in 20-30 minutes once mixed and you can’t extend its working time once it starts to thicken. Mix in a clean container with a margin trowel. Add water gradually. Aim for a peanut-butter consistency — holds its shape on the trowel, doesn’t run, doesn’t crumble.

Let the mixed grout slake for 5 minutes (chemical activation), then re-stir before applying. Skipping the slake gives weaker grout.

Step 7: Float the grout into the joints, diagonally

Hold the rubber float at 45° to the floor. Drag the grout across the tiles diagonally — across the joint pattern, not along it. Diagonal angle pushes grout into the joints and across the tile face; if you drag along the joint, you pull grout out as you go.

Work a small area at a time — about 1 m² per batch. Press firmly, fill every joint completely. Then drag the float at a 90° angle to skim excess grout off the tile face.

Step 8: First wipe with a damp sponge — and the timing matters

Wait. The grout needs to set up for 10-15 minutes before sponging — too soon and you pull grout out of the joints; too late and the haze is hard to remove. The test: press a fingernail into the grout in a joint. If it leaves a small dent and the grout doesn’t smear, ready to sponge.

Sponge: damp (not wet) — wring it out hard. Wipe the tile face in a circular motion, lifting grout off the surface. Rinse the sponge in the rinse bucket (not the clean water — you’re contaminating the clean water reserve), then again in clean water. Repeat over the whole area.

Don’t drag the sponge along the joints — you’ll dig grout out. Always perpendicular to or across the joints.

Step 9: Second wipe and haze removal after 1 hour

An hour later, a thin haze appears on the tile faces — that’s grout residue. Buff with a dry microfibre cloth in a circular motion. The haze comes off in seconds. If it doesn’t, the grout has set too hard and you need a grout haze remover (Davco TileShield) — but on properly-timed work the dry buff is enough.

If joints look low (sunken below the tile edge), the grout slumped — usually because you wiped too soon. Mix a little more grout, fill the low joints, sponge again.

Step 10: Silicone the movement joints, seal the grout

All internal corners (wall-wall, wall-floor) and around any bath, shower base, vanity, sink — silicone, not grout. Run a 5 mm bead, smooth with a wet finger or silicone tool, peel masking tape immediately while wet.

72 hours after grouting, apply a grout sealer (Aqua Mix Sealer’s Choice Gold, or Davco Sealer). Roll-on or brush-on. Sealer protects against staining and water penetration, and is the difference between grout that looks new in 5 years and grout that’s brown in 18 months.

Step 11: Cure time — keep the area dry for 72 hours

Sanded grout cures over 72 hours. Light foot traffic OK after 24 hours; full water exposure (showering, mopping) only after 72. If it’s a shower, no using it for 3 days. If it’s a kitchen splashback, no boiling pasta water splashes for 3 days. Premature wetting weakens the cement bond and you get crumbly joints in 6 months.

Block the shower off with a bag-and-tape sign so a household member doesn’t forget and use it.

Step 12: Document the colour and date for future patch work

Write the grout colour code (Davco “Stone” or Mapei “100 White”) and the install date on a piece of masking tape stuck inside the vanity or under the sink. In 5 years when you need to patch a corner crack or re-do one joint, you’ll know exactly what to buy. Otherwise you’re matching grout swatches in Bunnings, which is a frustrating exercise that never quite works.

The Steve rule

The Steve rule for regrouting is: multi-tool removes, sanded grout fills, silicone movement joints. Grout saws are pain in the neck for half-hearted DIY. Multi-tool with a carbide grout blade is the actual tool. Sanded grout per AS 3958 means the wet area waterproofing warranty stays valid. Silicone in corners means the joints don’t crack in 6 months. Get those three right and a regrout job lasts 15 years and the bathroom looks new again.

Got a regrout that came out brilliant (or one that taught you a lesson)? Send us a write-up.