Flood testing a membrane. What the standards say.

A flood test is the cheapest insurance on a waterproofing job. It finds the pinhole at the waste before the tiles go down, not after the ceiling below stains.

Is a flood test compulsory?

Showers and wet areas (AS 3740)

Visual inspection: must. Flood test or leak detection: optional.

Balconies and roofs (AS 4654.2)

An inspection, a test, or both when the membrane is finished. A 24-hour water test is the standard's guide.

Your contract

The builder's inspection and test plan can make it compulsory on the job.

So the standard does not force a flood test. Most builders and certifiers ask for one anyway, and FORSPEC recommends it.

The method, if you test

1. Wait for full cure. The membrane must be fully cured before it is flooded or wetted in any other way. The cure time is on the product's data sheet.
2. Plug the waste inside the pipe. Use a test plug or a flood test balloon set below the flange. Tape over the grate does not test the join between the membrane and the flange.
3. Fill to the top of the waterstop. Where a hob or waterstop splits the shower from the bathroom floor, test each side on its own.
4. Hold for at least 24 hours. Mark the water level at the start.
5. Check three things: has the level dropped, is there water outside the area, is the membrane damaged.
6. Write it down: the drop in level, any leak seen, and its cause.

The standard gives no allowance for evaporation. FORSPEC's reading is simple: a drop you cannot explain, or any water outside the area, is a fail. Repair, let it cure, and test again.

Balconies and roofs

The external standard does not give a depth, a way to dam the edges or a record form. Before you flood a balcony, check with the engineer that the slab can take the weight of the water, protect the door sill, and photograph the level at the start and the end.