Glass & Tile Drill Bits: How to Drill Through Tiles Without Cracking Them

You've finished tiling the bathroom. The adhesive is set, the grout is done, everything looks sharp. Now you need to drill six holes for the towel rail, the toilet roll holder, and a mirror. You pick up a standard masonry bit, set the drill to hammer action, and press it against the tile. The glaze shatters. A crack runs diagonally across two tiles. Those tiles cost £8 each, the tiler charged £40 per square metre to fit them, and you've just created a problem that's expensive to fix and impossible to hide. Replacement tiles from the same batch may not be available. All of this is avoidable with a £10 set of bits and five minutes of technique.

What they are and when you need them

Glass and tile drill bits are specialist bits designed to cut through glazed ceramic, porcelain, and glass without cracking the material. They look different from any other drill bit you own. The most common type has a spear-shaped carbide tip (two angled cutting edges meeting at a sharp point) rather than the twisted flutes of a masonry or HSS bit. That spear point scores through the hard glaze with a scratching action instead of the hammering action that shatters tiles.

You use them with a standard combi drill set to rotary mode (no hammer, no impact). They fit standard drill chucks. The operation is slow and deliberate, nothing like drilling into timber or even masonry.

You'll need these bits whenever you're fixing anything to a tiled wall: towel rails, shower screens, bathroom cabinets, shelving, toilet roll holders, soap dishes, kitchen splashback accessories. Any time a screw needs to go through a tile and into the wall behind it.

Types: carbide vs diamond

This is the decision that matters. Get it wrong and you'll destroy bits, crack tiles, or both.

Carbide spear-point bits

The classic "glass and tile" drill bit. A tungsten carbide tip ground to a spear point. These are cheap (£3 each, £8 – £13 for a set) and work well on standard glazed ceramic wall tiles, the kind you'd find in most UK bathrooms and kitchen splashbacks. They also handle non-toughened glass.

They do NOT work on porcelain. Porcelain is fired at much higher temperatures than ceramic, making it considerably harder. A carbide bit will skate across the surface, overheat, and go blunt within seconds. If you try to force it, the tile cracks.

Lifespan on ceramic: 30-50 holes from a decent set before the tips dull noticeably.

Diamond-tipped bits

A steel core coated or tipped with industrial diamond grit. These cut through everything: ceramic, porcelain, natural stone, and glass. They cost more (£15 – £20 per individual bit, £20 – £36 for a set) but they're the only option for porcelain tiles.

Diamond bits come in two sub-types. Some have a spear-point shape similar to carbide bits. Others are small cylindrical core bits that grind a ring rather than drilling a hole. Both work; the spear-point style is easier to start accurately.

Lifespan varies wildly depending on the material. On standard ceramic, a diamond bit will last 100+ holes. On hard porcelain (grade 5 hardness, the type used for floor tiles), professional tilers report as few as 3-4 holes per bit before it's spent. That's not a defective product. Hard porcelain genuinely destroys drill bits.

How to tell if your tiles are ceramic or porcelain

Look at the edge or the back of a tile. Ceramic tiles have a clearly different colour on the body compared to the glazed surface. The back is usually a pale, chalky, slightly rough material. Porcelain tiles are the same colour all the way through, the body and surface are virtually identical. Porcelain also feels denser and heavier for its size.

If you're unsure, treat it as porcelain and use diamond bits. The only cost is spending more on bits. The cost of guessing wrong the other way is cracked tiles.

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How to drill through tiles properly

The technique matters more than the bit. A premium diamond bit used badly will still crack your tile. A budget carbide bit used correctly will make a clean hole every time in ceramic.

Before you start

Check for pipes and cables. Use a pipe and cable detector on the wall before marking any hole positions. Bathroom walls often have hot and cold water pipes running behind tiles, and kitchens frequently have electrical cables for sockets. A burst pipe behind freshly tiled walls is a disaster that dwarfs a cracked tile.

Buy spare tiles. If you haven't already, try to get one or two spare tiles from the same batch before drilling. Practice on a spare, and have a replacement ready if something goes wrong. Matching tiles from a different batch often have slight colour variations that are visible once fitted.

The drilling process

1. Apply masking tape

   Stick two strips of masking tape in a cross pattern over the drilling point. The tape does two things: it gives you a surface to mark on with a pencil, and it provides friction for the drill bit to grip. Without tape, the bit's tip skates across the shiny glaze and you lose control of where the hole goes. Press the tape down firmly.

2. Mark the hole position

   Use a pencil or fine marker to put a clear crosshair on the tape. Double-check your measurement. Moving a hole by even 10mm means drilling another hole through the tile, and the wrong one is permanently visible.

3. Set your drill correctly

   Switch your combi drill to rotary only mode. Turn the hammer/impact function OFF. This is the single most important step. Hammer action vibrates the tile and cracks it instantly, no matter what bit you're using. Set the speed to low: 400-600 RPM for porcelain, 600-900 RPM for ceramic. If your drill doesn't show RPM, use the lowest speed setting and keep trigger pressure light.

4. Start the hole

   Place the bit tip on your mark. Apply light, steady pressure. Don't push hard. Let the bit do the cutting. The first few seconds are the critical ones, because until the bit bites into the surface, it wants to wander. Some people start at a slight angle and then straighten to 90 degrees once the bit has a small divot to sit in. Both approaches work. What doesn't work is jamming the bit down hard and hoping for the best.

5. Cool the bit regularly

   Every 20-30 seconds, pull the bit out and either dip it in a pot of water or spray the hole with a water bottle. Overheating is the main cause of bit failure and tile cracking. The bit tip changes colour when it overheats (turns blue or straw-coloured). If you see that, stop and cool it down before continuing. Some premium diamond bits are marketed as "dry drill" but they still last longer with water cooling.

6. Switch bits once through the tile

   The moment you break through the tile into the substrate behind (you'll feel the resistance drop), stop. Swap to a standard masonry bit for the rest of the hole depth into the wall behind. Tile bits wear rapidly in masonry and brick, so every second you spend drilling into the wall with a tile bit is unnecessary wear. Match the masonry bit to the same diameter as your tile bit.

The wall plug trap

This catches people out constantly and no product listing or retailer guide mentions it.

When you drill through a tile and insert a wall plug, the plug must pass completely through the tile and seat into the wall behind. If the plug sits inside the tile's thickness, tightening the screw expands the plug against the inside of the tile. The tile cracks from the inside outward. You won't see it happening until the crack appears on the surface.

Drill deep enough that the plug slides past the tile and anchors entirely in the masonry behind. For a typical 8-10mm wall tile, that means the hole in the wall behind needs to be at least 25-30mm deep. Push the plug in until it's flush with or slightly below the tile surface. And in wet areas (showers, bath surrounds), run a bead of clear silicone around the plug before inserting it to stop water wicking behind the tile through the hole.

What size bit for which wall plug

This is driven by wall plug sizes, not tile sizes. Every UK wall plug has a colour code that tells you the drill bit diameter.

For most bathroom accessory fitting, you'll use 6mm and 8mm bits. A 4-piece carbide set covering 4mm, 5mm, 6mm, and 8mm handles 90% of tiling drill jobs in ceramic.

For porcelain, buy individual diamond bits in just the sizes you need. A single 6mm diamond bit costs £15 – £20. Buying a full set when you only need two sizes is wasteful if each bit only lasts a few holes.

What to buy

Budget: carbide sets for ceramic tiles (£8 – £15)

If your tiles are standard glazed ceramic (the most common type in UK bathrooms and kitchens), a budget carbide set is all you need.

Toolstation Toolpak 3-piece set at £8.48. Basic but effective. Individual bits from £2.18 (3mm) to £3.68 (10mm) if you only need specific sizes.

Wickes 3-piece set at £10, or their 8-piece set at £17.8 covering 3mm to 10mm. The 8-piece is good value if you want full size coverage.

Screwfix Titan 4-piece set at £12.99 (4mm, 5mm, 6mm, 8mm). Tungsten carbide tipped, straight shank, 4.1/5 stars from 66 reviews. This is the set most people should start with for ceramic tiles. It covers the four most useful sizes and costs less than a single diamond bit.

Bosch CYL-9 individual bits from £3 each (6mm at Screwfix). A step up from own-brand carbide. The 5-piece set is £26.19 covering 5.5mm to 10mm. Good quality but at that price you're approaching diamond bit territory.

Mid-range: diamond sets for porcelain and all tile types (£20 – £36)

Screwfix Erbauer 4-piece diamond set at £35.99 (6mm, 8mm, 10mm plus a drill guide jig). Diamond-tipped, hex shank, rated for porcelain, ceramic, and glass. 4.3/5 stars from 86 reviews. The included drill guide is genuinely useful, as it holds the bit in position during the critical first few seconds. This is the recommended purchase if you have porcelain tiles or a mix of tile types.

Bosch EXPERT HEX-9 Hard Ceramic individual bits from £15.36 (varies by size). These are the professional-grade choice. Bosch claims they last up to 10 times longer than their CYL-9 range on hard ceramic. Sizes from 3mm to 12mm. Handles hard ceramic, porcelain, natural stone, and glass. Buy individually in just the sizes you need.

Professional: dry diamond bits for heavy porcelain work (£20 – £30 per bit)

If you're drilling multiple holes through grade 5 porcelain floor tiles (the hardest common tile type), budget diamond bits will burn through quickly. Professional-grade options last longer per bit.

Marcrist PG750X-HEX from £25.85 per bit. Dry-drilling diamond technology, hex shank. Marcrist claims 30-70 holes in grade 5 porcelain at around 35 seconds per hole. That's a meaningful step up from budget diamond bits that die after 3-4 holes in hard porcelain.

Marcrist PG350X-HEX from £19.62. Slightly lower spec than the PG750X but still a clear upgrade from retail diamond bits.

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When to use a hole saw instead

Spear-point tile drill bits max out at around 10-12mm diameter. Beyond that size, you need a diamond hole saw (also called a diamond core bit for tiles). The transition point is clear.

Up to 10mm: spear-point tile bit. For wall plugs and small fixings.

15mm and above: diamond hole saw. For pipe pass-throughs (15mm copper pipe needs a 20-22mm hole), shower valve access, bath trap holes (typically 35mm), and extractor fan ducting.

Diamond hole saws are a different tool with a different technique. They're cylindrical, they cut by grinding a ring, and they need even more water cooling than spear-point bits. They're covered in the hole saw set guide.

Where you'll need this

• Tiling - drilling fixing holes for bathroom accessories and kitchen splashback fittings, plus pipe pass-throughs for plumbing connections

Common mistakes

Using hammer action. The number one cause of cracked tiles. Every forum thread, every professional guide, every tile manufacturer says the same thing. Rotary only. If your drill doesn't have a rotary-only mode (some budget drills don't), don't use it on tiles.

Using a masonry bit instead of a tile bit. Standard masonry bits have a blunt chisel tip designed to chip through brick and concrete. On a tile, they chip the glaze and crack the surface. The £3 it costs for a proper tile bit is cheaper than a single replacement tile.

Drilling too fast. Speed generates heat. Heat cracks tiles and burns out bits. Keep below 900 RPM on ceramic and below 600 RPM on porcelain. If you're seeing smoke or the bit is changing colour, you're going far too fast.

Not cooling the bit. Water isn't optional for porcelain, even with bits marketed as "dry drill." Diamond bits CAN dry-drill, but they last dramatically longer with regular water cooling. A spray bottle costs £1.

Seating the wall plug in the tile instead of the wall. The plug must pass through the tile completely. Tighten a screw into a plug that's gripping inside the tile body and the expansion force cracks the tile from the inside.

Skipping the masking tape. The glazed surface of a tile is like glass. Without tape, the bit tip slides across it the moment you start drilling. Two strips of masking tape in a cross pattern gives the bit something to grip.