SoukLocal Workmanship Standard

Waterproofing: what to check before the tiles go down

A leak under new tiles means breaking the bathroom out again. Waterproofing takes a day or two to do right, and five minutes to check, if you check before it is covered.

Illustration, not to scale. Numbers are checked on the page below, each with its basis.

2+coats of membrane, the second at right angles to the firstManufacturer
24 hminimum before tiling or testing, longer when coolManufacturer
24 hflood test with the water level markedGood practice
150 mmmembrane turned up the walls, full height in the showerGood practice

The short answer

Good bathroom waterproofing is a proprietary membrane applied in at least two coats over a clean, sloped screed, with corners and pipes reinforced, turned up the walls, left to cure, and then flood-tested before tiling. The one check that matters most: see the flood test yourself, with the water level marked, before any tile goes down.

By SoukLocal AdvisorUpdated 29 October 2026

Why check before it is covered. Once tiled, a failed membrane can only be fixed by removing the tiles, the adhesive and often the screed, and the leak may already have damaged the ceiling below or the flat next door.

The checklist

Each check shows its basis: Manufacturer Published standard Good practice. Hold points, in coral, are the moments to see the work before it is covered.

Before the membrane

After the screed has cured, before any waterproofing

The screed already falls towards the drain1:100 Waterproofing follows the surface under it. If the screed is flat, water sits on the membrane forever. Good practice
The surface is clean, dry and free of dust, oil and loose bits Membranes bond to the surface, not to dust. Poor bonding is the start of most failures. Manufacturer[1]
Cracks wider than about 2 mm are filled and taped first2 mm A crack that moves will tear the membrane above it. Manufacturer[1]
Corners, wall-floor joints and every pipe are reinforced with tape or a bandage Corners and pipes are where membranes split. The data sheet names the tape and the pieces. Manufacturer[1]
You know the membrane brand and product, and have its data sheet The data sheet sets the coats, thickness and cure time. Without it, nobody can say the job was done right. Good practice

Applying the membrane

The day it goes on

Mixed in a clean bucket with a drill paddle, only as much as can be used in its working time Old or badly mixed material does not cure properly. Good practice
First coat covers everything, with no pinholes or thin patches Thin spots are leak paths. Good practice
Where the system uses mesh, it is pressed flat into the wet first coat Mesh adds strength only when it is fully embedded, not floating on top. Good practice
The second coat goes on after the recoat time, at right angles to the first4 h One common membrane needs 4 hours at 23 °C between coats, longer when cool. Crossing the direction covers thin spots. Manufacturer[1]
Membrane runs up the walls at least 150 mm, and full height around the shower150 mm Water runs down walls and splashes. A floor-only membrane leaks at the edges. Good practice
Total thickness matches the data sheet1 mm One common membrane needs at least 1.0 mm dry. Ask how the applicator checks it. Manufacturer[1]

Flood test

After the cure time, before any screed protection or tiles

Hold point: Do not allow tiling until you have seen this test pass

The membrane has cured for the time on the data sheet before testing24 h+ Testing too early can damage the membrane. Cool or humid weather needs longer. Manufacturer[1]
The drain is plugged and the floor is filled with water, about 2 to 5 cm deep, with the level marked A marked level makes the result visible to anyone. Good practice
After at least 24 hours the level has not dropped, and there is no damp below or next door24 h A drop or a damp patch below means a leak. Find it now, while it is cheap. Good practice
A dated photo of the full floor and the mark at the start and the end Your evidence if a leak appears in the defects period. Good practice

After tiling

At handover

Tile adhesive is a type suited to wet areas, on top of the membrane, not instead of it Water-resistant adhesive and grout do not replace a waterproofing system. Published standard[2]
Flexible sealant at every wall-floor joint, around the tray, basin, WC and bath These joints move. Grout cracks there; sealant does not. Good practice
Run the shower for five minutes: water drains with no pooling Pooling means the fall is wrong, and water will find any weak point. Good practice

Get the full waterproofing checklist, free

All 18 checks, including the hold point. Tick them on site, add notes and photos, and download a PDF to send your contractor. Free with a SoukLocal account.

Questions to ask your contractor

Which membrane, which product, and can I have the data sheet?
When is the flood test, and can I see it with the level marked?
How far up the walls does the membrane go, and around the shower?
If a leak appears in the defects period, who removes and replaces the tiles?

Questions

How long should a bathroom flood test last?

Good practice is at least 24 hours, with the drain plugged, 2 to 5 cm of water and the level marked, after the membrane has cured for the time its data sheet states. Check that the level has not dropped and that there is no damp below or next door before tiling.

Is tile adhesive or grout enough to waterproof a bathroom?

No. Water-resistant adhesives and grouts are not a substitute for a waterproofing system. Wet areas need a proprietary membrane or tanking system under the tiles.

How many coats of waterproofing does a bathroom need?

At least two, as the membrane maker specifies, with the second coat applied after the recoat time and at right angles to the first. Corners, joints and pipes are reinforced first.

Can waterproofing be checked after tiling?

Only by running water and looking for leaks, which is too late to fix cheaply. The time to check is before tiling: see the membrane, the reinforced corners and the flood test.

Sources

Written from the working method statements of a Dubai design-and-build contractor, then checked against manufacturer data sheets and published guidance. Each check says which. Manufacturer figures are examples from one product or system: follow the data sheet for the product used on your job. This page helps you ask the right questions; it is not a certificate that work is sound.

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