How to Re-Grout a Tiled Floor or Wall
Regrouting is the job that seperates 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 handheld grout saws with a carbide blade. They work, slowly, and 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. Twenty years on the tools and I still see homeowners trying to scrape grout with screwdrivers — don’t be that person. The Aussie wet-area gotcha: AS 3958 specifies that grout in joints over 3 mm wide in wet areas must be sanded. Don’t drift off this standard.
What you’ll need
- An oscillating multi-tool (Bosch PMF, Makita TM3010C, Ryobi One+ R18MT or Ozito MTK)
- A grout-removal blade — Bosch ATZ 52 or Diablo carbide ($20–$30)
- A vacuum cleaner with a brush attachment
- New grout — Davco SureColour Sanded or Mapei Ultracolor Plus Sanded for joints over 3 mm
- A rubber grout float
- Two buckets — one clean water, one rinse
- A large grout sponge (the $8 yellow-and-white ones at Bunnings)
- Microfibre cloths
- Masking tape
- Knee pads — you’ll need them
- A P2 dust mask and safety glasses
- Silicone for movement joints (Selleys Wet Area or Sika Sanisil)
- Grout sealer for 72-hour follow-up (Aqua Mix Sealer’s Choice Gold or Davco Sealer)
Step 1: Identify what you’re grouting and where
Floor or wall? Kitchen splashback or shower? 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 under AS 3958; internal corners (wall-to-wall, wall-to-floor, around bath or shower base) — silicone, never grout; around bath rim — silicone only, movement joint. If the existing job has grout in the corners, plan to silicone those instead during the regrout. The number of leak callbacks I’ve done because someone grouted a movement joint and it cracked within months would buy me a new caulking gun every year.
Step 2: Tape off adjacent surfaces and set up dust control
Mask off the bath, vanity, skirting and anything you don’t want the multi-tool dust on or scratched by a skipping blade. The multi-tool blade will skip if you sneeze, and grout removal dust gets everywhere. Drop sheet on the floor. Open a window. Run an extractor fan. P2 mask before you start the tool — old grout dust is silica-heavy and you don’t want it in your lungs.
Step 3: Set up the multi-tool with the grout blade and depth stop
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. 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 existing waterproofing. AS 3740 is clear that anything that breaks the waterproof membrane is licensed work — see how to re-silicone a bathroom properly for the silicone side of wet-area work.
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 turns to powder and the blade sinks to the depth stop. Keep the blade dead-centre. If it kicks toward a tile edge, the carbide grit scratches 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 — it’s the difference between a 15-year regrout and a 6-month regrout.
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 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. Hill’s water down here is hard, so if you’re in the Adelaide Hills like me, use rain water or filtered water — calcium in the hard tap water can produce efflorescence in the cured 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; 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 off the tile face.
Step 8: First sponge wipe — 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, you’re ready. 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 bucket — you’re contaminating your 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 in a circular motion. The haze comes off in seconds. If it doesn’t, the grout has set too hard and you need Davco TileShield — but on properly-timed work the dry buff is enough. If joints look sunken, the grout slumped — mix a little more, fill the low joints, sponge again. See how to remove mould from grout for the maintenance side.
Step 10: Silicone movement joints and seal the grout at 72 hours
All internal corners (wall-wall, wall-floor) and around any bath, shower base, vanity or sink — silicone, not grout. Run a 5 mm bead, smooth with a wet finger or silicone tool, peel masking tape immediately while wet. Sanitary-grade neutral-cure only. Then 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. Write the grout colour code and install date on masking tape stuck inside the vanity — in 5 years when you need to patch a corner crack you’ll know exactly what to buy.
When to call a tradie
A surface regrout (cut to half joint depth, refill) is a homeowner job. The moment you discover the substrate is failing — soft, springy floor near the bath, water staining on the ceiling below, swelling timber framing visible through an inspection hatch — the waterproofing membrane has likely been compromised and you’ve crossed into licensed waterproofer territory under AS 3740. Don’t try to patch a failed membrane yourself. Same goes for cracked or hollow-sounding tiles (lift one and the membrane below is exposed), or any sign of structural movement in the bathroom subfloor.
Common screw-ups
- Grouting movement joints (corners, around bath rim) — cracks in months, leaks behind tiles.
- Using non-sanded grout in wide wet-area joints — fails under shower water, voids waterproofing warranty.
- Going too deep with the multi-tool blade and hitting the membrane below — instant repair job.
- Wiping with too-wet sponge or dragging along joints — washes the grout out before it cures.
- Skipping the 72-hour sealer step — grout stains within months of normal use.
Cost & time
Multi-tool hire from Bunnings or Kennards: $45 a day. Grout blade: $20. 5 kg bag of Davco SureColour Sanded: $35. Float, sponge, masking tape, sealer: $40 total. Roughly $140 in consumables for an average bathroom regrout. Time: 6–8 hours of actual work spread across two days (grout removal day one, regrout day two), plus the 72-hour sealer step. A tradie quote for the same job: $800–$1,400 depending on bathroom size.
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 lasts 15 years and the bathroom looks new again. Twenty years on the tools and the principles haven’t changed — just the price of the multi-tool. Do it once, do it properly.
