Regrouting a shower floor looks like a two-hour job right up until the first tile edge pops off. The grout is soft, the tile is hard, and most tools you own are matched to the wrong one. I found this out in a 1998 guest bathroom where I chipped three tiles in the first ten minutes, then spent the rest of the weekend finishing it properly. The fix wasn't a better tool. It was slower passes, a shallower depth stop, and starting from the right side of the joint.
What you will learn
- Why grout removal chips tile, and which edge fails first
- Which bits remove grout and which ones just polish it
- How to set a depth stop so you never touch the backer board
- What to do differently with epoxy grout
- How clean the channel has to be before new grout will bond
Why does grout removal chip tile at all?
Because you're working between two hard edges with a tool that wants to wander. Cement grout is softer than the tile around it, but the gap is narrow, and the moment the bit touches glazed porcelain the edge fractures in a crescent you can't hide. Chips almost always happen on the tile you're pushing toward, not the one you're pushing away from, because that's where the bit is loading up. That single detail changes how you move: always work so the bit is cutting in the direction that puts pressure on the grout, not on the arris. The other thing people miss is that the last third of the old grout is the dangerous part. When the channel is nearly clear the bit drops deeper, and a drop of two millimetres is the difference between clean and cracked.
What bit actually removes grout?
A carbide grout removal bit with a guided head, not a straight burr. The guided ones have a smooth nose that rides on the tile face and keeps the cutting flutes in the joint. A plain cylindrical burr removes material fine but has nothing stopping it from walking sideways, which is how the crescent chips happen. For wider joints (4mm and up) the flat-sided removal bits work faster; for the hairline stuff you'll want the narrowest head you have and more patience. Diamond-impregnated blades are the other option and they cut cleaner, but they're slower and they load up with dust if you don't clear the channel as you go. The HARDELL Orange Pro 61pcs corded kit ships with the removal bits and the collets to match, which matters more than people think — a bit that's a hair undersize in an oversized collet will wobble and you'll blame the tile.
How do you set the depth so you never hit the backer?
Measure first, then stop. Old grout is usually 6 to 10mm deep in a floor and shallower on a wall. Pull one loose fragment out with a pick, measure it, and mark your bit with a piece of tape at two-thirds of that depth. You don't need to remove all of it. New grout needs roughly 3mm of clean channel to key into, and going all the way to the backer board buys you nothing except a waterproofing membrane you might puncture. On floors I stop at about 8mm even when the joint is 12mm deep. The tape on the bit is a visual stop, not a physical one, so keep your wrist light — the bit will happily go deeper if you lean on it. If you're working on a flex shaft the whole thing gets easier because the weight of the tool isn't hanging off your hand. The Grey Ultimate 153pcs kit with flex shaft is the setup I reach for on anything over a few square metres.
Hand tools or rotary for the corners?
Hand tools, and it isn't close. Inside corners and the transition where floor meets wall are where you'll do damage, because the bit can't stay square to the joint and the guide nose lifts off the tile. A cheap carbide grout rake takes maybe forty seconds per metre and it will never chip a corner. I use the rotary for the open runs — the long straight joints where the guide stays planted — and switch to the hand rake within about 100mm of any inside corner. Same for the perimeter where the tile meets the tub or the shower base. That joint is usually caulk, not grout, and if you find caulk you should stop and recaulk rather than continue.
What speed and pressure actually work?
Mid-range speed and almost no pressure. On a dial that runs to 35,000 I'm somewhere around 15,000 to 20,000 for cement grout. Faster doesn't cut faster, it just heats the bit and glazes the dust into a paste that packs the flutes. Pressure is the bigger mistake: people push because they want to see progress, and pushing is what lifts the guide off the tile face. Let the carbide do it. You should be producing dust, not chips of grout. If you're getting chunks, you're either too slow or too deep. Dust also means you need extraction or at least a shop vac held nearby, because silica dust in a small bathroom is genuinely unpleasant to breathe and it settles on everything.
What changes with epoxy grout?
Everything gets slower and heat becomes the enemy. Epoxy doesn't crumble like cement grout, it softens and smears, so a dull bit will just rub it into a glossy film that new grout won't bond to. Use a fresh carbide bit, drop the speed a little, and clear the channel constantly. Some people soften epoxy with a heat gun first — it works, but keep the heat low and keep it moving, because you can craze the glaze and you can absolutely crack a natural stone tile. If the epoxy is less than about fifteen years old, it may not be worth removing at all. Epoxy doesn't need regrouting on the same schedule as cement, and plenty of "failing" epoxy just needs a deep clean.
How clean does the channel need to be before regrouting?
Clean enough that you can see the original colour of the grout bed, with no glossy smear on the tile sidewalls. Vacuum the channel, then wipe it with a barely damp sponge and let it dry completely. Damp grout beds are the most common reason new grout shrinks and cracks within a month — the old bed pulls water out of the new mix before it cures. On a floor I'll vacuum, wait a day, and come back. Also check your joint width while you're in there. If the old joints varied between 3mm and 6mm, the new line will read as sloppy no matter how carefully you float it, and that's the moment to decide whether you're regrouting or retiling. A 6-inch IP54 caliper tells you the actual joint width in about three seconds per spot, which beats eyeballing it eleven times and getting it wrong.
What's a realistic timeline for one shower?
A standard tub/shower surround is roughly 12 to 16 square metres of tiled surface, and a first-timer should plan two sessions. Removal is the slow part — budget three to four hours if you're being careful, less if the grout is already crumbling. Cleaning and drying is an hour plus overnight. Regrouting itself goes fast, maybe ninety minutes, and then you're into cleanup and a sealer coat. The mistake is trying to do removal and regrout in one day. You'll rush the cleaning step and the new grout pays for it.
From the workshop: the bathroom that taught me the depth stop
The 1998 bathroom had 4mm joints and I went in with a bare carbide burr and no tape on the bit, because I'd read that you should take the grout out "all the way." Three tiles chipped on the wall beside the vanity — all on the same side, all from pushing toward the edge. I stopped, pulled a fragment, measured it at 9mm, and taped the bit at 6mm. Zero chips for the rest of the room. The bigger lesson came a week later when I regrouted: I'd cleaned the channels the same evening I opened them, didn't let them dry, and the new grout hairline-cracked along about a metre of the back wall by spring. Same job, two mistakes, two very different repair bills. These days I do removal on a Saturday and grout on the Sunday, and I haven't had a callback on my own work since.
Common mistakes recap
- Cutting all the way to the backer board instead of two-thirds depth
- Pushing toward the tile edge instead of along the joint
- Using a plain burr with no guide nose
- Running too fast and glazing the dust into the channel
- Regrouting the same day, before the old bed has dried
- Using the rotary in inside corners
FAQ
Can I remove grout without any power tool?
Yes, with a carbide rake and time. It's about three times slower on open runs and much safer in corners, so plenty of people do the whole job by hand on a small backsplash.
Will a rotary tool scratch the tile glaze?
Not if the guide nose stays planted. Scratches happen when the bit tilts and the shoulder of the cutting head rides on the glaze, which is what happens when you lean into the cut.
How do I know if it's epoxy or cement grout?
Scratch it with a pick. Cement grout powders and feels sandy; epoxy resists and comes off in rubbery curls. Epoxy also usually has a slight sheen and doesn't darken much when wet.
Do I need to remove 100% of the old grout?
No. Around two-thirds depth or a minimum of 3mm of clean channel is enough for new grout to key in. Going deeper only adds risk.
What if I hit the waterproofing membrane?
Stop that joint immediately. Patch it with the membrane manufacturer's compatible product before regrouting. A small puncture is cheap to fix now and expensive to find in two years.
Is a flex shaft worth it for this job?
On floors, yes. It takes the tool's weight off your wrist and you'll notice it about an hour in, when your control starts to drift.
How do I keep dust down?
A helper with a shop vac held right at the bit, plus a respirator. Mist the surface lightly if you must, but don't flood it — wet grout dust turns into a paste that packs the flutes.
Can I regrout over the top instead?
You can, and it fails. A skim coat over old grout has almost nothing to grip and usually cracks or powders out within a year. It's a listing-photo fix, not a repair.
