Tile Drill Bits: Which Bit Won't Crack Porcelain

Picking the right tile drill bit is the difference between a clean 6mm hole and a cracked tile you have to chop out and replace. Most split tiles are not down to clumsy hands: they are down to a masonry bit, hammer action left switched on, or a blunt bit that is grinding rather than cutting. Get those three right and drilling a tiled wall is a two minute job. This is how we do it on bathroom and kitchen work across Bromley and south east London, including the awkward cases: hard porcelain, natural stone, and old tiles bedded on cement render.

Which tile drill bit suits your tile

There are three bit types worth owning, and the choice follows the tile, not the price.

Spear point (tungsten carbide) bits are the cheap arrowhead bits sold as glass and tile bits. They cut glazed ceramic and glass well. On porcelain they blunt in seconds and then skate or overheat, so treat them as a ceramic-only tool.
Diamond tipped bits have industrial diamond bonded to the tip or rim. They are the only sensible choice for porcelain, and they also handle marble, slate, mosaic and vitrified paving. Marcrist’s PG850 range, a common trade bit, is rated for drills and cordless drills up to 1500 to 3000 rpm, lists sizes from 6mm to 112mm, and is quoted at 500 to 700 holes per bit at roughly 27 seconds a hole. Those numbers are a useful sanity check: if your hole is taking several minutes, something is wrong with the bit, the speed or the pressure.
Diamond core bits, sometimes sold as crowns or hole saws, cut a ring rather than a solid hole. They are for anything above about 20mm: pipe tails, shower valve bodies, waste outlets.

Why porcelain is the problem child: it is fired denser than ceramic and absorbs no more than 0.5 per cent water by weight under BS EN 14411, the standard that classifies tiles. That density is what makes it hard-wearing underfoot and hard on drill bits. Natural stone varies more: slate and travertine cut easily, some granites are as stubborn as porcelain. Our note on porcelain versus ceramic covers the difference in use as well as under the drill.

Set the drill up before the bit touches the tile

Three settings decide whether the tile survives.

Hammer action off. This matters more than the bit. Percussion works by smashing a hard tip into masonry thousands of times a minute, and a glazed tile is a brittle sheet sitting on adhesive over a void. Hammer action will star-crack it before the bit is through the glaze. On a combi drill, turn the collar to the plain drill symbol, not the hammer symbol. If you only own an SDS drill, switch it to rotary-only or borrow a normal drill.

Low to moderate speed. Diamond cuts by abrasion and abrasion makes heat. Heat is what kills the bit and stresses the tile. Stay near the bottom of the manufacturer’s stated range, keep the trigger steady rather than pulsing it wildly, and let the bit do the work.

Light pressure. Leaning on the drill does not speed anything up. It glazes the diamond and loads the tile at the exact moment the tip breaks through the back face, which is when most cracks happen.

Drilling the hole, step by step

Mark the hole and check what is behind it. Measure twice. Keep the hole in the body of the tile, not on a grout joint: a plug set half in grout and half in tile will never pull up tight, and the bit tends to wander into the softer joint.
Stop the bit skating. On glazed ceramic, a cross of masking tape over the mark gives the spear point something to bite. With a diamond bit, the better trick is to start the bit tilted at roughly 45 degrees so the rim cuts a small crescent through the glaze, then bring the drill upright once that notch is established.
Keep it wet. Water is the single biggest factor in bit life. A sponge held under the hole, a plant mister, or a blob of plumber’s putty shaped into a dam around the mark will all work. On a wall, where running water is awkward, rolling the bit on a wet sponge between bursts is enough for small holes.
Lift the bit clear every few seconds. This lets water and air reach the tip and clears the slurry that otherwise polishes the diamonds smooth.
Ease off at breakthrough. When the resistance drops, reduce pressure to almost nothing. A bit that suddenly plunges is how tiles chip from the back.
Switch bits for the substrate. Once through the tile, swap to a masonry bit for the wall behind, and keep hammer action off until the bit is well clear of the tile.

Holes closer to a tile edge than about their own diameter are the riskiest. A drilling guide plate clamps or suctions to the tile and holds the bit square, which lets you work near an edge and overlap holes without the bit walking.

Big holes for pipes, wastes and shower valves

Once a hole is bigger than about 20mm, a solid bit is the wrong tool. A diamond core cuts only the ring of material, so there is far less heat and far less load on the tile. Cores come in the diameters plumbing actually uses, and a typical core runs on an arbor with a spring-loaded pilot drill that centres it until the rim has scored its own track.

A diamond core hole saw shown with its arbor and spring-loaded pilot drill — A diamond core hole saw with its arbor and pilot drill. The same tooling pattern is used for large holes in tile. | Diamond core hole saw LEC 68D by Dmitry G (CC BY-SA 3.0), via Wikimedia Commons, https://commons.wikimedia.org/w/index.php?curid=18161861

Two practical points. The pilot needs somewhere to go, so check there is a void or soft substrate behind, and cores throw real slurry, so water is not optional. Where a large hole would land tight to an edge, it is often quicker to lift that one tile, core it on a bench with the tile supported on a flat board, and re-fix it.

What sits behind the tile

The tile is the easy part. What you drill into next decides whether the fixing holds and whether the job is safe.

Cables. BS 7671, the UK wiring regulations, sets out prescribed zones where concealed cables are expected to run: within 150mm of the top of a wall, within 150mm of the internal or external angle where two walls meet, and in the vertical and horizontal bands running from any socket, switch or other accessory. Cables buried less than 50mm from the surface normally rely on 30mA RCD protection, and the IET publishes a brief overview of the requirements for cables concealed in a wall or partition. Treat those zones as no-drill areas, and use a detector even so, because older installations in period houses do not always follow them.

Pipes. Assume a vertical pipe runs up to every tap, cistern and radiator valve. A detector on its metal setting will usually find copper.

The fixing. Behind bathroom tiles you will typically find plasterboard, a tile backer board, or solid masonry. Each needs a different plug: a hollow wall anchor for board, a standard wall plug for brick or block. Which one you have is worth knowing before you start, and our comparison of tile backer board and plasterboard explains how each behaves. Older Bromley terraces often have a bed of sand and cement render behind the tiles, which takes a plug well but chews through cheap masonry bits. Whatever the fixing, size the pilot hole in the tile so the plug passes through cleanly. Forcing a plug through a slightly tight hole is a classic way to crack a tile after the drilling went perfectly.

Dust and eye protection

Tile dust contains respirable crystalline silica, which the Health and Safety Executive treats as a serious construction health risk alongside wood and cement dust. For a couple of holes at home the exposure is small, and the controls are easy: drill wet, since water suppression is the most effective way to stop dust becoming airborne, or use on-tool extraction, covered in HSE information sheet CIS69. Wear eye protection too: tile swarf is glass-hard and sharp enough to cut fingers when you wipe it away.

Why tiles crack, and how to avoid each cause

Hammer action left on. The most common single cause, and completely avoidable.
A blunt or wrong bit. A spear point on porcelain glazes over and starts generating heat instead of cutting. Change the bit rather than pushing harder.
Heat. Dry drilling puts a hot ring into a cold tile, and that stress can craze the glaze around a hole that otherwise looks perfect.
A void behind the tile. If it was fixed on dabs rather than a full bed, nothing supports it where you are pushing. Tap first: a hollow ring means less pressure and more patience.
Drilling too near an edge. Move the hole if you can, use a guide plate if you cannot.

If a tile does crack, do not try to fill it. Rake out the grout and lift the tile while you still have spares. For help with that, or with a full bathroom or kitchen, see Bromley Tilers.

Frequently asked questions

Can I use a masonry bit on tiles?

On soft glazed ceramic a sharp masonry bit sometimes gets through, but it is the wrong geometry: it is designed to chip material away under percussion, not to cut a glaze. On porcelain it will not start at all. Use a spear point for ceramic and a diamond bit for porcelain.

Do I need a special drill?

No. An ordinary corded or cordless drill is fine, as long as you can turn hammer action off and control the speed. Trade diamond bits are typically rated to run at up to a few thousand rpm, so a standard drill is well within range.

Should I drill into the tile or the grout line?

Into the tile. Grout is softer, so the bit drifts, and a plug set in a joint has far less to grip. The exception is a temporary or very light fixing where you want to leave the tiles unmarked.

How do I stop the drill bit slipping on a shiny tile?

Masking tape over the mark works for spear point bits. For diamond bits, start the cut with the drill tilted so the edge of the bit scores a notch, then straighten up. A drilling guide plate removes the problem entirely.

Does drilling into a tile mean water can get behind it?

Any penetration through tile and grout in a shower or splash area is a potential route for water. Seal the hole: put a bead of silicone into it before the plug and fixing go in, and seal around the fitting once it is on the wall.

020 8058 5574

contact@bromleytilers.co.uk

Tile Drill Bits: Which Bit Won’t Crack Porcelain