The most common failure pattern: tiles were installed without a proper waterproof membrane underneath. The shower runs, water gets past the grout joints, soaks into the concrete, and starts breaking down the adhesive bond. After 12–24 months, tiles sound hollow when tapped. Within another year, some are rocking or lifting. This is not a tile quality problem. It is a waterproofing problem.
Before any tile adhesive goes down in a wet area, a waterproof membrane is applied to the substrate. Common products in Bali: cement-based waterproofing slurries (Sika, Aquaproof) applied in 2 coats, or sheet membranes. The membrane covers all floor areas, walls to at least 300mm height (full wall height in shower areas), all pipe penetrations, and all corners with reinforcing mesh. The membrane must cure fully (24–48 hours) before tiling begins.
Tap the floor and wall tiles. A solid sound means good adhesive contact. A hollow sound means the adhesive did not penetrate or the tile has delaminated — either way, a sign of future problems. Also check grout around the shower base — if it is cracking or dark-stained, water is getting in.
For a new renovation: ask to see the membrane applied before tiling starts. If the tiler cannot show you the membrane, assume it was not done.
The damage is rarely visible at first, which is exactly why skipping waterproofing is so tempting for a crew under time pressure. For the first year everything looks perfect. Then water that has been quietly soaking into the screed starts to show: a musty smell, dark staining at the base of the wall, grout that goes soft or drops out, and eventually tiles that sound hollow and begin to rock. In a two-storey home the first sign is often a stain on the ceiling of the room below. By then the fix is no longer a re-grout — it is a strip-back and re-do.
The two systems we use most are cement-based waterproofing slurries — brushed or rolled on in two coats — and self-adhesive or liquid sheet membranes for trickier details. Both work when applied correctly: full coverage across the floor, up the walls to the right height, lapped into corners with reinforcing mesh, and sealed around every pipe penetration and floor waste. The product matters less than the care taken at the corners and penetrations, which is where leaks almost always start.
Waterproofing and floor fall work together. Even a perfectly membraned floor will pool water and stain if the slope to the drain is wrong or absent. We form a consistent gentle fall toward the waste before tiling and check it with a level — water should run to the drain from every point in the wet area, not collect in a corner.
Insist on seeing the membrane applied and cured before any tile goes down. Take a photo. A reputable tiler will happily show you. If they cannot, or they are ready to tile the day after demolition with nothing visible underneath, stop and ask. It is far cheaper to query it now than to strip the bathroom back in eighteen months.
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