Quick Answer

Grind concrete in tight spaces and closets with a 100-125 mm angle grinder fitted with a diamond cup wheel, not a walk-behind machine. A hurricane cup wheel on a 125 mm grinder handles up to 5-10 sqm of closet floor; for 20-30 sqm tight rooms, a small 270 mm single-disc hand grinder with a round backer is faster. Work in short 30-second bursts to avoid overheating the tool, and run a HEPA vacuum at the same time. Tight spaces are exactly where walk-behind tooling cannot reach, so plan hand tooling before the job starts.

Why Walk-Behind Grinders Fail in Tight Spaces

A standard walk-behind grinder is 480-600 mm wide, needs 600 mm of clearance to turn, and has a safety bumper that sticks out another 100 mm. In a closet (800 x 1500 mm), a bathroom (1.5 x 2.5 m), or under a stair, it simply will not fit.

Angle Grinder Technique

Holding a 5 kg angle grinder for 4 hours a day is hard on the wrists and shoulders. Technique matters as much as tooling.

• Use a 125 mm grinder, not 180 mm - the 180 mm wheel is too heavy for overhead and close work.
• Keep the wheel flat - tilt it and you will gouge the slab.
• Short passes, overlap 30% - like painting a wall.
• Let the diamond cut - do not lean on the tool; pressure creates gouges.
• Cooling breaks - 30 seconds on, 30 seconds off; cup wheels glaze if they overheat.
• HEPA vacuum wand next to the wheel - dust is worst in enclosed closets.

For profiling, a L-segment cup wheel cuts a smooth, even scratch pattern without leaving gouges. For removing thin glue or paint overspray, switch to a small PCD cup wheel.

When to Bring in a Small Walk-Behind

If the room is 20+ sqm and you can fit a 270 mm single-disc machine through the door, it is worth it. A 270 mm grinder with a round backer pad and three small trapezoids covers 10-15 sqm/h, about 3x faster than an angle grinder. Measure the door first - and measure the machine handle folded down. Most 270 mm grinders fit through a 760 mm door.

For very tight edges, finish with the angle grinder after the walk-behind. The combination - walk-behind for the field, angle grinder for the edges - is how pros handle small rooms.

Health and Dust in Enclosed Spaces

Dust in a closet does not disperse - it settles on every surface. Without a HEPA vacuum, the room will be unusable for days.

• HEPA extractor - minimum 1200 cfm, attached to the grinder shroud.
• Plastic barrier - seal off the doorway to the rest of the house.
• Negative air machine - optional but speeds cleanup.
• Respirator - P100, not a dust mask.
• Wet cleanup after - mop with clean water twice.

Frequently Asked Questions

Q: Can I use a multi-tool with a diamond blade for tiny spots?

For 0.1 sqm of glue, yes. For a whole closet, no - the blade is too small and cuts grooves.

Q: How do I grind under an overhang or stair with low clearance?

A flat cup wheel on a 100 mm angle grinder held horizontally. Do not use a tall cup wheel - it will not fit.

Q: What grit should I use in a closet?

Same as the rest of the slab: 30/40 for paint prep, 60/80 for coating prep, 100+ if you are polishing. Match the grit to the adjacent floor.

Q: How long does a closet take to grind?

3 sqm with an angle grinder: 45-60 minutes including edges. Plan half a day for a bathroom-sized space.

Conclusion

Tight spaces are hand-tool territory. Keep 100/125 mm cup wheels on the truck, run HEPA dust collection, and match the grit to the adjacent floor. JOY TECH stocks low-profile cup wheels and small trapezoid discs for the 270 mm hand grinders that fit through closet doors.