Quick Answer

To grind concrete under a door frame or in low clearance, use a small 100 or 115 mm angle grinder with a diamond cup wheel, protect the door frame with masking tape and a thin metal shield, and grind in shallow, overlapping passes from the doorway inward. Measure the gap with a feeler gauge or a piece of flooring material as you go. Never force a large grinder into a tight spot; a smaller tool gives you control and avoids damaging the frame or the door.

Why You Need to Grind Under the Frame

When a new floor covering (tile, luxury vinyl, hardwood, carpet) is installed, the finished height rises by 10 to 20 mm. The existing door no longer closes. Instead of planing the door or cutting the frame, it is often easier to grind a small amount off the concrete slab under and around the door frame. This gives the clearance needed for the new floor and keeps the door operating at its original height.

Measure the Clearance You Need

Before grinding, work out exactly how much material you need to remove. Stack samples of the new flooring material on the existing slab, close the door, and see how much it binds. Measure the gap between the bottom of the door and the slab, then subtract the required clearance (usually 3 to 5 mm for a door sweep or 2 to 3 mm for a normal door). That number is how deep you need to grind. Mark it with tape on the frame so you do not go too deep.

Tool Selection

• 100 or 115 mm angle grinder: small enough to fit under most door frames and give you control in tight spaces.
• Diamond cup wheel, 30/40 or 60 grit: coarse enough to cut concrete, fine enough to leave a smooth surface.
• Dust shroud if possible: many small grinders accept a compact shroud connected to a vacuum.
• Flat pry bar or screwdriver: to hold the door open and out of the way.
• Masking tape and thin aluminium or sheet metal shield: to protect the frame.

Do not use a large 180 mm grinder in a doorway; it will not fit, it will grab the frame, and you will lose control.

Protect the Door Frame and Door

Tape the bottom of the door frame with several layers of masking tape to prevent the cup wheel from scratching the paint or wood. For extra protection, slide a thin sheet of aluminium or hardboard between the frame and the grinding area. Remove the door if possible; if not, prop it fully open and tape a protective cover over the bottom edge. Cover nearby walls and furniture with plastic sheeting because grinding dust spreads everywhere.

Grinding Technique

Start at the Center of the Doorway

Fit the cup wheel, put the guard on, and start the grinder away from the surface. Lower the wheel flat onto the concrete in the middle of the doorway. Make slow, overlapping passes, moving from the center toward each side. Do not press down; let the wheel cut.

Work Toward the Frame

When the center area is at the right depth, work the wheel toward the sides of the opening, keeping the wheel flat. On the last 10 mm next to the frame, tilt the grinder slightly so only the edge of the cup contacts, and keep it moving. Do not dig the wheel into the corner where the frame meets the floor.

Check Often

Stop every few passes and close the door or lay the flooring sample down. It is easy to grind too deep in a small area; shallow passes and frequent checks keep you on target. Use a straightedge to make sure the ground area blends smoothly with the surrounding slab.

Low-Clearance Spots

If the clearance under the frame is so tight that even a 100 mm grinder will not fit, you have a few options:

• Use an angle grinder with a thin-profile cup wheel and remove the guard (only if you can control the tool safely).
• Use a rotary hammer with a chisel bit to chip out the top layer, then clean up with the grinder.
• Plane the bottom of the door instead of grinding the slab, if the door is thick enough.

Cleanup and Final Fit

When you have reached the target depth, vacuum the area thoroughly. Close the door and check the swing; it should clear the new flooring height with the planned gap. If the door still binds, mark the spot and touch it up. Once the fit is good, remove the tape and protective sheeting. The ground concrete may look lighter than the surrounding slab; this fades over time and is covered by the new flooring.

Safety Notes

Wear eye protection, hearing protection and a respirator; doorways are tight and dust gets everywhere. Two hands on the grinder at all times. Keep the cord or battery clear of the spinning wheel. If the wheel catches the frame or the door, release the trigger immediately. Do not grind in a cramped, awkward position where you cannot control the tool.

Bottom Line

Grinding concrete under a door frame is a precision job: small grinder, sharp diamond cup wheel, protected frame, shallow passes, and frequent checks. Measure twice, grind once, and stop when the door closes properly.