Bosch 3-1/2 in. x 1/8 in. Starlock oscillating multi-tool kerf carbide grit grout grinding blade

A grout blade that trades speed for control—and earns its keep

I reached for the Bosch Starlock grout blade on a bathroom regrout where cracked lines ran through tight joints and around a tub surround. An oscillating tool won’t match a grinder’s pace, but this blade makes up for it in control, precision, and a surprising amount of staying power.

Design and compatibility

This is a segmented, 3-1/2-inch carbide-grit blade with a 1/8-inch kerf and about 1-1/2 inches of immersion depth. The segmented shape lets you run long, straight sections without overcutting into adjacent tile, and it gives you access right up to inside corners and fixtures. The 1/8-inch thickness is a good match for most sanded grout lines (3/16 and up feel especially comfortable), and it’s workable on 1/8-inch joints if you use a light touch. For very narrow, unsanded joints around 1/16 inch, this blade is simply the wrong tool—you’ll risk scuffing or chipping tile edges.

The Starlock mount is a highlight. It seats with a positive, rigid connection, and the blade stays locked at whatever angle you set it. That rigidity translates into less chatter, fewer slips, and cleaner shoulders along the grout line. If your multi-tool is Starlock-ready (Bosch, Fein, and others), it’s a direct fit. On older OIS-style tools, compatibility is generally good, but an adapter may be required. Check your specific model before you buy—some non-Starlock tools don’t accept closed-face accessories without an adapter.

Bosch’s color-coding and laser-etched markings are minor conveniences that I ended up using more than I expected. The markings stayed readable after multiple passes in gritty dust, and being able to glance at the blade and confirm it’s the grout grinder—not a wood tooth blade—saves headaches.

Performance in grout and abrasive materials

In sanded cement grout, the blade tracks straight and cuts predictably. Carbide grit doesn’t “cut” so much as abrade, and that’s a benefit here: you’re less likely to grab or catch an edge the way a toothed blade can. I ran my multi-tool in the middle of its speed range and let the grit do the work. With a slight rocking motion, the blade cleared 1/8-inch joints in one or two passes without burning or glazing over. Around the tub flange and fixtures, the ability to clock the blade at odd angles helped me keep the tool body out of the way while maintaining a flat, guided stroke.

On tougher mixes—older, cured sanded grout with a dense aggregate—the blade still moved at a steady pace. It’s slower than a diamond wheel on a grinder, no question, but the payoff is minimal risk of tile chipping and far better control along irregular lines. In thinset and light skim coats, it’s effective for spot cleanup or shaving proud ridges, though the 1/8-inch kerf means you’re working a band rather than a feathered edge.

For epoxy grout, carbide will do the job, but longevity drops. If I were facing a full room of epoxy or urethane joints, I’d reach for a diamond-grit accessory; for cement-based grout and thinset cleanup, this carbide blade feels like the right balance.

Dust, heat, and control

Grout removal is dusty by nature. This blade doesn’t include dust extraction features, so plan on an assistant with a vac or clip a nozzle near the cut. Heat was a non-issue for me at moderate oscillation speeds with a vacuum pulling fines away. If you do see the grit loading up, a quick brush with a wire card or a tap out restores bite. I didn’t experience glazing, which sometimes happens when you force a carbide accessory at high speed.

Control is where the Bosch shines. The Starlock interface keeps things tight, and the segmented profile gives you a defined reference surface. I could run the blade with the flat edge riding on the glaze and the grit cutting only the joint, which dramatically reduces accidental scuffs. It’s not foolproof—lean the blade into the tile and you’ll mark the surface—but the geometry favors a neutral, guided stroke.

Durability and value

I used one blade to strip out the majority of a small bathroom, including several sections of stubborn, sand-heavy grout, and it still had plenty of life afterward. The grit wears evenly rather than shedding in chunks, and the core stayed straight. Hitting metal, however, is still a quick way to shorten its life. Nails from transition strips or screws at backer seams can be present along thresholds; when I suspected metal, I proceeded slowly and pivoted to a metal-capable accessory for the last bit.

Is it more expensive than generic OIS grout blades? Yes. But the work rate stays consistent longer, which matters more than headline speed in delicate regrout work. Fewer blade changes, less frustration, and better control are real productivity gains, especially in finished spaces.

Where it fits—and where it doesn’t

• Ideal use cases:

  • Removing cement-based, sanded grout in floors, showers, and backsplashes
  • Cleaning thinset squeeze-out and small ridges before setting trim or fixtures
  • Trenching shallow channels in plaster or drywall for small patches or clips
  • Working up to edges, fixtures, and corners with minimal risk of overcutting

• Less ideal:

  • Very narrow, unsanded grout lines (~1/16 inch). Choose a thinner grout blade or a rotary bit.
  • Large-scale epoxy/urethane grout removal. A diamond-grit accessory is faster and will outlast carbide.
  • Aggressive tile shaping or cutting. This is an abrasive grinder, not a tile-cutting wheel.

Technique tips that mattered

• Protect the glaze: Two strips of painter’s tape flanking the joint give you visual guidance and a sacrificial layer. The blade rides on the tape and keeps incidental scuffs off the tile.
• Let the grit do the work: Moderate speed, steady pressure, and a gentle rocking motion clear material efficiently. Forcing the cut just creates heat and dust.
• Keep it clean: Vacuum at the source. Dust build-up insulates the grit and slows the cut. Periodically knock the blade clean; a brass or steel brush restores bite.
• Mind your depth: With 1-1/2 inches of immersion, you can easily go deeper than the grout bed. I scored once along the surface, then made a second pass to full depth only where necessary, especially near edges.
• Watch for hardware: Near thresholds and backer seams, slow down and listen. A change in pitch often means metal. Switch to a metal-capable blade to avoid trashing the carbide grit.

Build quality and ergonomics

Bosch’s steel core is stiff and resists warping. The grit distribution on my blade was uniform out of the package, and there were no thin spots or voids along the cutting edge. The Starlock footprint adds some mass compared to older slotted OIS accessories, but the tradeoff is worthwhile for the rigidity and quick, tool-free swaps. The ability to orient the blade precisely—especially clocked slightly off-axis to keep the tool handle clear of walls—was an everyday convenience.

The bottom line

The Bosch grout blade is a purpose-built accessory that prioritizes control, accuracy, and longevity in cement-based grout and similar abrasive materials. It isn’t the fastest way to remove grout, and it’s not the right choice for hairline joints or extensive epoxy runs. But for most residential regrout tasks, it offers a calm, predictable cut, excellent visibility, and a mount that keeps the tool feeling planted.

Recommendation: I recommend this blade for anyone using an oscillating tool to remove cement-based grout or clean up thinset in finished spaces. It costs more than generic options, but it holds its edge, stays controllable across long runs, and saves tile edges from accidental nicks. If your joints are narrower than 1/8 inch or you’re tackling epoxy grout over a large area, look instead to a thinner or diamond-grit accessory. Otherwise, this is the grout blade I’d keep in the kit.