Hollow Sounding Tiles: When to Leave Them, When to Lift

Hollow sounding tiles are tiles that give a dull, papery knock instead of a solid click when you tap them, because there is air between the tile and the floor or wall behind it. On their own they are not always a fault. A hollow corner on a small wall tile in a dry room can sit happily for twenty years. A hollow patch on a large porcelain floor tile, or anywhere inside a shower, is a different matter, because that is where tiles crack, grout breaks up and water gets in. This page shows you how to test, how to read what you find, and when the tiles need lifting.

Why a tile sounds hollow

A tile only sounds solid where adhesive fills the space behind it and has bonded to both faces. Anywhere there is a gap, the tile rings like a drum skin. The usual causes, roughly in order of how often a tiler finds them:

Spot fixing or “dot and dab”. Blobs of adhesive on the back of the tile, or on each corner, leave most of the tile unsupported. It never gives a solid bed.
The wrong trowel for the tile. A small notch under a large tile leaves ribs of adhesive that never collapse into a full bed, so you get channels of air.
Adhesive that skinned over. Adhesive spread over too big an area dries on the surface before the tile goes on. The tile sits on it but never grips.
No back-buttering. Large format tiles and tiles with deep ribs on the back need a thin coat on the tile as well as the bed, or the hollows in the back stay empty.
Movement after fixing. A flexing timber floor, a screed that was still wet, or no movement joints in a big floor can break a bond that was fine on day one. That is why a floor that was solid can start to sound hollow years later.

How to test for hollow tiles

Tap each tile with a coin or the handle of a screwdriver: centre, each corner, each edge. Tap a tile you know is solid first so you have a reference sound, and mark every hollow area with masking tape.

What you are looking for is the pattern:

One corner of a tile. Usually a gap at the end of a trowel rib or a spot that missed the adhesive. Low risk.
The whole centre of a tile with solid corners. That is the classic spot-fixed tile. Possibly fine on a wall; on a floor the middle has nothing under it.
A cluster of hollow tiles together. Something happened to that area: the base moved, the adhesive went off before the tiles went down, or water has got in. Find out which before you touch it.
Hollow tiles with cracked grout or a crack through the tile. The bond has failed and the tile is moving under load. That is past the watching stage.

What BS 5385 expects

The British Standard for wall and floor tiling, BS 5385, is what a professional tiler works to. Part 1 covers internal walls and was updated in 2018. The Tile Association’s summary of the 2018 changes sets out the points that matter here (TTA presentation on BS 5385-1:2018):

Wall tiles with a face area of 0.1 m² or more, which is anything from about 300 x 333mm up, should be solidly bedded.
Tiles that weigh more than 70% of what the wall can carry should be solidly bedded whatever their size. The TTA’s own example is 9mm porcelain at about 18 kg/m² on gypsum plaster, which carries 20 kg/m²: 18 is more than 70% of 20, so those tiles need a solid bed.
A 50% contact area does not give enough bond for large format tiles and thin panels.
Large format tiles, and tiles with ribbed or heavily keyed backs, should be fixed by floating and buttering: a combed bed on the wall and a thin coat over the back of the tile.

Floors are stricter than walls, because every tile carries feet, furniture and dropped pans. Floor tiles should be on a solid bed of adhesive with no voids, which is why dot and dab is never acceptable on a floor. In practice that means the right notch size, back-buttering anything large, and pressing each tile in with a sliding action so the ribs collapse.

The standard does not say one hollow tap means a failed job. It tells you the method the tiler should have used.

When you can leave hollow tiles alone

Plenty of hollow tiles never cause trouble. You can usually leave them if all of these are true:

The hollow area is small, often a single corner or edge.
The tile is on a wall in a dry area, not in a shower or behind a bath.
The grout around it is complete, with no hairline cracks.
The tile does not move, click or rock when you press it.
Nothing heavy is fixed through it, such as a towel rail or a basin.

Photograph which tiles are hollow and tap them again every six months. If the hollow area grows or the grout cracks, move on to the next section.

When hollow tiles need lifting

These are the cases where leaving them costs you more later:

Floor tiles cracked and lifted in a ridge across a tiled floor — Floor tiles that have cracked and pushed up off the floor. Photo for illustration, not a Bromley Tilers job. | Cracked tile flooring by Mk2010 (CC BY-SA 4.0), via Wikimedia Commons, https://commons.wikimedia.org/wiki/File:Cracked_tile_flooring.jpg

Floor tiles with hollow centres. A heel, a chair leg or a dropped tin of beans can snap an unsupported tile. Large porcelain floor tiles are the worst for this, because they span further over the gap.
Anything in a wet area. In a shower or wet room a void behind a tile is a place for water to sit. If the grout cracks, water gets behind the tiles and into the wall or floor. If you already see staining or a damp patch, read our page on water leaking through shower tiles.
Cracked grout around a hollow tile. The tile is moving. Grout will keep cracking until the tile is fixed.
A spreading cluster. If more tiles sound hollow each time you test, the bond is failing across the area.
Tiles lifting or “tenting”. When a floor has no room to expand, tiles can push up into a ridge and pop off the floor. That needs a movement joint, not just new adhesive.

How to fix a hollow tile properly

The reliable repair is to take the tile off and refix it. For a single tile:

Rake out the grout all the way round with a grout rake or an oscillating tool, so the tile is free from its neighbours.
Lift the tile. A hollow tile often comes off in one piece with a wide chisel, which means you can reuse it. If it breaks, you need a spare.
Scrape all the old adhesive off the floor or wall and off the back of the tile, if you are reusing it. New adhesive on top of old ribs leaves the tile proud and creates new voids.
Prime if the surface needs it. Our page on tile primer covers which surfaces do.
Spread a fresh bed with the right notch for the tile size, back-butter the tile, press it in with a slight slide and check it is flush with the tiles around it.
Tap it once the adhesive has set. It should sound solid all over. Then regrout.

Our step-by-step guide to fixing loose tiles goes through the lifting stage in more detail, and if the tile cracks on the way out, see how to replace a cracked tile.

What about resin injection? You will see kits that inject resin through a small hole in the grout line to fill the void without lifting the tile. You cannot see where the resin goes or confirm it has filled the void, and it does nothing about why the tile went hollow. We do not use them on floors or in wet areas.

Hollow tiles on a new job

If your tiles are only weeks or months old and you are finding hollow areas, talk to whoever fitted them before you do anything yourself. A few hollow corners on a new wall are normal. A floor where most tiles sound hollow in the middle, or large format wall tiles that sound hollow across the face, suggest the method was wrong. A good tiler will come back, test with you and lift one tile so you can both see the adhesive coverage on its back.

If you are getting a floor or wall tiled now, ask up front how the tiler fixes large format tiles. The answer you want is a solid bed, back-buttering and the right notch for the tile size. If you are in Bromley or south east London and want a second opinion on hollow tiles, Bromley Tilers can test the floor and tell you honestly whether it needs touching.

Frequently asked questions

Are hollow sounding tiles a problem?

Not always. A small hollow corner on a wall tile in a dry room with intact grout is usually fine to leave. Hollow centres on floor tiles, hollow tiles in a shower and any hollow tile with cracked grout around it are problems, because those are the tiles that crack or let water in.

Why do my floor tiles sound hollow after a few years?

The bond has broken since the floor was laid. Common reasons are a timber floor that flexes, a screed that was not dry when it was tiled, no movement joints in a large floor, or water getting under the tiles. Spot-fixed tiles can also let go slowly under daily foot traffic.

Can you fix hollow tiles without removing them?

Resin injection kits exist, but you cannot see whether the resin has filled the void and they do not deal with the cause. Lifting the tile, cleaning off the old adhesive and refixing on a solid bed is the repair that lasts.

How much of a tile should be covered in adhesive?

Floor tiles, and wall tiles in wet areas, should be on a solid bed with no voids. Under BS 5385-1:2018, wall tiles of 0.1 m² or more, and tiles heavy enough to use more than 70% of what the wall can carry, should also be solidly bedded. Smaller tiles in dry areas can be fixed with a notched bed, but you still want as much contact as you can get.

Will hollow tiles crack?

They are more likely to. A tile with nothing under its centre can snap under a point load such as a heel, a chair leg or something dropped on it. Large thin porcelain tiles are the most at risk. Wall tiles in dry areas rarely crack from being hollow alone.

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