Short answer: before a single tile goes into a Bali wet room, a tiler should see a continuous membrane across the floor and up the walls, reinforced at every corner and pipe, fully cured and flood-tested — and a floor that falls to the drain from every point. If any of those is missing, the tiles will fail no matter how well they are laid. This is what we check, in the order we check it, on every bathroom tiling job.
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.
A membrane is only as good as the surface it sits on, so the inspection starts before any product is opened:
Once the membrane has cured we plug the drain, fill the floor with a shallow layer of water and leave it — usually overnight — then check the level and the ceiling or walls on the other side. A membrane that holds water with nothing on top of it will hold under tile; one that loses water gets fixed now, while it costs a brush and a tin of product rather than a strip-out. If a tiler is ready to tile the day after the membrane goes on, there has been no cure and no test.
The same logic applies anywhere tile sits over a room or a structure that must stay dry. Upper-floor balconies and roof terraces need a membrane under the screed, a fall away from the building and outlets that can take a tropical downpour — see outdoor and terrace tiling. Pools need a system rated for permanent immersion, checked at the coping, steps and every light or pipe penetration before any mosaic goes on — see pool tiling. In every case the tiler's job is to refuse to tile over a membrane that has not been proven.
How long should a membrane cure before tiling?
Follow the product's data sheet; for the cement-based slurries common in Bali that typically means 24–48 hours between the final coat and tiling, longer in cool, damp weather. The flood test comes after the cure, not instead of it.
Can I tile over my old bathroom tiles without a new membrane?
Only if the old floor never leaked and every tile is solidly bonded. If there are stains below, hollow tiles or crumbling grout, the old membrane has already failed and tiling over it hides the problem rather than fixing it.
Who is responsible for the membrane — the tiler or the waterproofer?
On many Bali jobs it is the tiler. Whoever applies it, the tiler should inspect and flood-test it before laying tile, because the tile work will be blamed when it fails.
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. If your bathroom already leaks, our tile repair and bathroom tiling pages explain how we strip back and re-do a wet area properly.
Questions about a tile project in Bali? WhatsApp us — free advice, no obligation.