How do I cut a large hole in tile for a pipe or a tap?

A tap hole or a pipe entry through tile is the job that ruins a finished bathroom wall. The tile is hard, brittle and glazed, the core wants to skate, and the heat from dry cutting both destroys the diamond and cracks the tile. Porcelain is harder still. The technique is not difficult but it is specific, and it is nothing like drilling a small fixing hole.

Safety

What you'll need

• Diamond core hole saw of the correct size
• Drill with a low speed and no hammer action
• Water — a spray bottle, sponge or plumber's putty dam
• Guide jig, or a scrap board clamped to the wall (optional)
• Goggles and FFP3 mask
• Masking tape (optional)

Step by step

1. Establish what is behind the tile.A tap hole goes exactly where pipework runs. Use a detector, look at the fittings above and below, and if there is any doubt about a cable or a pipe, do not cut there.
2. Choose a diamond core, not carbide.Carbide-tipped tile saws work in soft ceramic and fail immediately in porcelain. A sintered or vacuum-brazed diamond core cuts both, and is the only sensible choice for anything over about 20mm.
3. Turn hammer action off and select a low speed.Percussion cracks tile instantly. Diamond cuts by abrasion, so speed generates heat without cutting faster. Gear 1 and moderate trigger.
4. Stop the core skating.Either use the guide jig that came with the core, clamp a scrap board with a matching hole over the tile, or start the cut at an angle. Some cores have a spring-loaded pilot; on glazed tile the angled start is more reliable.
5. Start at an angle and roll the core upright.Hold the drill at roughly 45 degrees so only a crescent of the rim contacts the tile, and cut a shallow groove. Once that groove will hold the core, bring the drill upright and cut the full circle.
6. Keep it wet, continuously.A helper with a spray bottle, a sponge held above the cut, or a ring of plumber's putty round the hole filled with water. Water is doing two jobs — cooling the diamond and carrying the dust away — and dry cutting fails at both.
7. Keep the core moving in small circles.Slight orbiting motion stops the swarf packing between the core and the tile and keeps the segments cutting. A core held dead still glazes over and stops.
8. Ease off as you break through.The last millimetre is where tiles crack and where the adhesive bed behind can grab. Reduce pressure, keep the water going and let it through.
9. Carry on into the substrate separately if needed.Once through the tile, a diamond core is not the tool for blockwork behind. Change to a masonry bit or an appropriate core, and switch hammer on only after the tile is fully cleared.

Tips

• Two crossed strips of masking tape over the spot help a core start on a slippery glaze and reduce chipping at the rim. They do nothing once the cut is established.
• Cutting a hole close to the edge of a tile is far riskier than in the middle. Where possible plan the layout so pipe holes fall away from edges, or cut a semicircle in two tiles instead.
• If the tile is already fixed and cracking it would mean removing a run of tiles, consider whether a smaller hole and a larger cover plate solves the problem instead.

Common mistakes

• Using hammer action for any part of the tile — Tile fails in tension and percussion cracks it from the first blow. Hammer goes on only once you are through into masonry behind.
• Cutting dry to keep the mess down — The core overheats within seconds, the bond holding the diamond breaks down, and the heat itself cracks the tile. Water is not optional.
• Leaning on the drill when progress slows — Diamond cuts by abrasion at a fixed rate. More pressure generates heat and packs swarf, which slows it further.

Questions people ask