Chips on a tiled floor almost always appear at breakthrough or at the start, not in the middle of the hole. The tile is a hard brittle skin over a softer body, and the moment the bit leaves that skin it grabs. Control those two moments and the hole comes out clean.

Where chips come from

Location	Cause	Fix
Ring at the start	Bit walked before it bit	Guide plate or a 45-degree start
Edge blown at exit	Pressure with no support	Back off in the last 5 mm, support the far side
Brown glazed edge	Heat, no water, too high rpm	Lower rpm, wet cut, fresh segment
Cracked tile	Hammer action	Rotary only, never hammer
Uneven hole	Bit wobble or worn core	Rigid bit, check runout

Sequence for a clean hole

1. Mark the hole and scan for pipes and cables before anything touches the tile.
2. Use a diamond tile bit, not a percussion bit. Hammer mode is the single biggest cause of cracked tile.
3. Start at low rpm with minimal pressure until a full ring groove is cut.
4. Keep water on the bit, or a wet sponge, to hold temperature down; dry cutting glazes and then chatters.
5. In the last 5 mm reduce pressure and let the bit cut through; support the far face if reachable.
6. Finish through the concrete body with the appropriate masonry or core bit.

What you can promise

On sound tile with a diamond bit and no hammer, a clean hole with a crisp edge is normal. On a tile already drummy or cracked, no bit rescues it: tap the tile first, and if it sounds hollow, price a replacement rather than a perfect hole. Drill a test hole in an offcut or a hidden corner on every new tile type.

Where the chips actually come from

Chipped tile edges are almost never caused by a bad bit. They come from impact, from heat, from a hole started off-centre, and from drilling with the tile's glaze left unsupported underneath.

Cause	What it looks like	Fix
Hammer action on entry	Crescent-shaped chips on one side	Rotary only, or start in a pilot plate
Bit skidding off the mark	Scratches then a ragged bite	Centre punch, masking tape, or a guide bush
Heat from a dry core	Crazing and small flakes around the rim	Wet cut, or slow dry with extraction
Breakthrough shock	Large chip on the exit side	Cut from both sides, reduce feed at exit
Void or unbonded tile	Chip extends beyond the hole	Check for hollow tiles before drilling

Two of those are operator errors and three are process decisions. Sorting which one you are looking at after the fact is harder than preventing all five, and prevention costs a few minutes per hole.

Sequence for a clean hole through tile and slab

• Tap the tile with a knuckle or a screwdriver handle. A hollow sound means the tile is unbonded and will break out regardless of technique; that tile gets replaced before drilling.
• Mark, then centre-punch through the glaze with a sharpened nail or a small masonry bit used by hand.
• Start with a small bit at low rpm and no hammer, just through the glaze. Once through, the hole guides the core.
• Drill the full hole from the tile side if the tile is on the accessible face, never from behind, unless both faces are accessible and the tile is on the far side.
• Support the exit: a wooden block clamped behind the wall, or drill both faces and meet in the middle.
• Cool water at the rim, not just at the crown, for anything above 30 mm.

The order matters more than the tools. Punching before drilling, piloting before coring and clamping before breakthrough removes most of the ways a tile edge can fail.

What you can promise a client, and what you cannot

No drilling method guarantees a chip-free edge on every tile. What can be promised is a defined process, a repair standard and a cost for the rare failure, which is what most clients actually need to hear.

• Promise: no impact action, pilot before core, exit support, and a wet cut where the finish permits.
• Promise: any chip larger than 2 mm on a visible edge will be repaired or the tile replaced at the contractor's cost.
• Do not promise: chip-free on hollow tiles, on tiles with existing hairline cracks, or on glazed porcelain at the edge of a large core.
• Do not promise: same result on a wall drilled from behind, where the exit side is the visible face.

Setting that expectation before the first hole is cheaper than arguing about a 4 mm chip after handover. It also protects the crew from being blamed for a tile that was already debonded.

Repairing the chip you could not avoid

Some chipped tile is unavoidable, and the difference between a complaint and an accepted result is how the repair looks and when it happens.

• Take the loose chips out before filling. A chip held only by glaze will come off again within weeks.
• Use a two-part epoxy tile filler matched to the tile colour, not cement grout, which shrinks and never matches.
• Fill slightly proud, cure fully, then shave the surface flat with a sharp blade rather than sanding, which dulls the glaze around it.
• Repair the same day the hole is drilled, while the tile is dry and clean. Waiting until the end of the job means working around furniture and dirt.
• Photograph the repair and note it in the handover: an accepted chip that is documented is a non-issue, an undocumented one becomes a defect six months later.

Budget a spare tile per room if the tiles are still available. It is cheaper than any repair method and it removes the argument entirely.

Charge for the water and the time. A dry fast hole is the one the customer photographs at handover.