Balconies
Why balcony tiles lift, crack or sound hollow
5 min read
Short answer
Tiles that sound hollow have lost their bond to the bed beneath. Outdoors the usual causes are thermal movement with nowhere to go, water sitting in the bed, or a bed that was never laid properly. It matters because a debonded area lets water travel sideways under the surface, so a small defect can appear a long way from where the water gets in.
Tap along a tiled balcony with a knuckle and the sound changes. Most of it is a solid tap; here and there it goes hollow, like knocking on a box.
That hollow sound is one of the more useful things you can find without lifting anything, and it is worth knowing what it means.
What "drummy" actually means
A tile is bonded to a bed underneath it. When that bond fails, an air gap forms, and tapping the tile makes it resonate. Trade shorthand for it is drummy.
One drummy tile in a corner is not much. A run of them, or a whole area, means the bond has failed across a section of the balcony, and that changes how water behaves: instead of sitting on the surface and draining, it can get into the gap and travel sideways.
That is why damage on a balcony often appears somewhere unrelated to the actual defect. The water entered at a cracked joint on one side and came out at a low point three metres away.
Why it happens outdoors more than indoors
- Thermal movement. A balcony in full sun heats and cools every day, and the tiles, the bed and the slab all expand and contract at different rates.
- No movement joints. If the tiled field has no allowance for that expansion, the pressure has to go somewhere, and it lifts or cracks the tiles instead.
- Water in the bed. A bed that stays wet loses strength, and freeze is not the issue in Perth, but constant saturation and salt movement are.
- Poor bedding. Tiles laid with inadequate adhesive coverage, or onto a dusty or contaminated surface, never had full bond to lose.
- Structural movement in the slab, particularly on a cantilevered balcony.
The tell-tale patterns
- Tiles lifting or tenting along a straight line, often near a wall or across the middle of the field, which usually means expansion with nowhere to go.
- A hollow area concentrated around the drain, which can mean water is sitting in the bed rather than leaving through the outlet.
- Cracking that follows the grout lines rather than crossing tiles, which points at movement in the bed.
- Cracks straight through tiles, which points at movement in the substrate beneath.
- Efflorescence at the joints in a drummy area: the white chalky deposit is left behind as water passes through the bed and evaporates, so it is direct evidence that water is in there.
Does it mean the waterproofing has failed?
Not by itself. The membrane sits below the bed, so tiles can debond while the membrane is still doing its job. Plenty of drummy balconies are not leaking.
What it does mean is that the surface is no longer behaving as a single sound layer, and that water has a path to move along under it. Combined with staining on the ceiling below, or ponding that will not drain, drummy tiles usually indicate the problem has already gone past the surface.
The only way to establish which situation you are in is to look at it, and on a balcony that often means opening up a small area rather than guessing from above.
What can be done about it
Where the debonded area is small and contained, and the membrane below is sound, individual tiles can be lifted and re-bedded and the joints made good.
Where it is widespread, or the falls are wrong, or the membrane has failed, replacing tiles one at a time is a holding action rather than a repair. The honest answer in that case is that the balcony needs opening up, and hearing it early saves paying twice.
In short
- A hollow tap means the tile has lost its bond to the bed underneath.
- Outdoor tiling moves. Without movement joints, that pressure lifts or cracks tiles.
- A debonded area lets water travel sideways, so damage can appear far from the defect.
- Drummy tiles alone are not proof the waterproofing has failed, but with ponding or staining below, they usually are.
Common questions
- Can hollow-sounding tiles just be left alone?
- A single isolated tile with no other symptoms often can be, and monitored. A run of them, or drumminess combined with ponding water, cracked perimeter sealant or staining on the ceiling below, is worth having looked at, because water is likely already moving under the surface.
- Why did my balcony tiles lift in a straight line?
- That pattern usually means thermal expansion with nowhere to go. Outdoor tiled fields need movement joints, and where they were left out the tiles are the weakest point when the field expands, so they tent or lift along a line.
- Can individual balcony tiles be replaced?
- Yes, where the area is small, contained and the waterproofing below is intact. Matching an existing tile can be the harder part, especially on an older balcony, so it is worth checking whether any spares were kept.
Related service: Balcony Leak Repair