Why does my floor tile sound hollow?

A hollow sound means there is air between the tile and the adhesive. It happens because the adhesive was spotted rather than combed, because the substrate moved, or because something got between the two.

What you'll need

• A coin for tapping
• A grout rake or a multi-tool
• A cold chisel and a club hammer
• Tile adhesive and a notched trowel
• Grout
• Eye protection

Step by step

1. Survey the whole floor.Tap every tile with a coin and mark the hollow ones. The pattern matters: scattered singles are a different problem from a whole area.
2. Check whether it actually matters.A hollow tile that is firmly grouted, level and not cracking may last for years. It is a defect worth watching rather than an emergency.
3. Look for the cause.Spot-fixing rather than full-bed adhesive is the usual one. Others are a flexing substrate, laying over a dusty floor, or adhesive that skinned before the tile went on.
4. Check the substrate movement.Hollow tiles over a timber floor usually mean the deck is deflecting. Stiffening the floor comes before any re-tiling, or the same thing happens again.
5. Rake the grout out around the tile.A grout rake or a multi-tool with a grout blade, all four sides, right down to the tile edge. This isolates the tile so the neighbours are not stressed.
6. Break the tile out from the centre.Drill a few holes in the middle and break outwards with a chisel. Levering from the edge transfers the shock into the adjacent tiles and cracks them.
7. Wear eye protection.Porcelain and ceramic fragments travel a long way at speed. This is one of the genuinely eye-threatening domestic jobs.
8. Clean the bed back to the substrate.All the old adhesive off, down to a sound surface. New adhesive over old ridges reproduces the hollow you have just removed.
9. Use the right adhesive and comb it.A flexible cement-based adhesive over timber or heated floors, combed with a notched trowel and back-buttered on the tile for full coverage.
10. Aim for full coverage.The standard for a floor is close to complete adhesive contact — around 95 percent in wet or heavily loaded areas. That is achieved by combing plus back-buttering, not by five dabs.
11. Let it cure before grouting.At least 24 hours. Grouting into uncured adhesive traps moisture and disturbs the bed you have just made.
12. Match the grout.Take a piece of old grout to match the colour, and expect a slight difference. New grout in an old floor is always a little brighter.

Tips

• A hollow tile that also rocks or has grout crumbling around it needs doing. A hollow tile that is silent underfoot and has sound grout can be left and monitored.
• If more than a few tiles in an area are hollow, get advice before starting. Re-bedding individual tiles on a failing floor is wasted effort.
• Keep spare tiles from every tiling job. Breaking one out is easy; finding a match ten years later is not.

Common mistakes

• Spot-fixing tiles with dabs of adhesive — Dabs leave voids that concentrate load on the contact points. A heel or a dropped pan cracks the tile over a void, and water that gets into the void has nowhere to go. Floors need combed, near-full coverage.
• Levering a tile out from its edge — The force goes straight into the adjacent tiles through the grout line. It is very common to break out one hollow tile and crack two sound ones, turning a small job into a large one.

If it doesn't work

Questions people ask