Toilet and bathroom waterproofing, done under the tiles and proved by a flood test.

Singapore price guides checked in September 2026 put the waterproofing membrane line at S$400 to S$1,500 within a bathroom renovation, and a full hack, re-membrane and re-tile of one HDB or condominium toilet at about S$3,000 to S$8,000 when a waterproofing contractor carries the whole job. Hacking and disposal alone is S$400 to S$1,500 and tiling S$1,500 to S$6,500; a no-hack repair from above is S$700 to S$2,500. The membrane material is the small part: two coats of Rayson SealForce WB20 on a typical toilet with its turn-ups take about 8 to 12 kg, under one 20 kg pail.

Hacking one to three weekdays, because HDB permits noisy work only on weekdays from 9 am to 5 pm and fixes the demolition days in the renovation permit; the membrane one day, in two coats a few hours apart; the flood test the following day, 24 hours after the final coat; then the screed, tiles and grout. On the Hougang trial application of SealForce WB20 photographed in September 2026, the membrane was complete the day after the approved hacking window closed and the flood test was under way the next afternoon.

A membrane cannot be applied over tiles: SealForce WB20 goes onto the prepared screed beneath them. A no-hack treatment is honest only for a narrow set of faults, such as water weeping through grout over a membrane that is still sound. If the bathroom has failed an HDB or HIP water test, water is already under the tiles, and injections or surface sealers buy months, not years. An assessment with a flood test tells you which case you have before anyone quotes for hacking.

After the final coat has dried for 24 hours and before any screed or tile goes down, the floor trap is plugged and the whole floor is flooded to a set depth and left for a full day while the ceiling below and the adjoining rooms are checked. It is the only proof that the membrane works. A quotation that does not include it is missing its most important line.

HDB restricts the hacking of bathroom and toilet wall and floor tiles in new flats for the first three years from key collection, to keep the original waterproofing and its warranty intact; hacking inside that window voids the waterproofing warranty. The compliant route is an overlay that leaves the tiles and the membrane beneath them undisturbed. Confirm the current terms on HDB's renovation guidelines before you plan.

In an HDB flat the floor slab between two flats is a shared structure, and HDB's Goodwill Repair Assistance scheme has been described in HDB's own letters as co-paying 50% of the repair cost, with the remaining half shared equally between the upper and lower owners and HDB arranging the contractor once both agree. In a condominium the strata law presumes the leak comes from the unit above unless proven otherwise, and both owners investigate jointly with the management corporation involved where needed. The repair is always done from the toilet above.

The practice Singapore specifications follow, drawn from the BCA good industry practices guide for internal wet areas, carries the membrane up every wall well above the finished floor, with about 300 mm as the common minimum, and to around 1,800 mm or full height on the walls that shower water strikes. It also rises behind the door threshold or kerb, and is dressed into the floor trap and up every pipe sleeve.

Rayson SealForce WB20, a one-part, water-based, polyurethane-modified membrane rolled straight from the pail in two coats at 0.4 mm wet film each. A typical 3 m² toilet with 300 mm turn-ups and a shower wall to 1.8 m takes about 8 to 12 kg, under one 20 kg pail. Where the wet area is heavier duty, a deck that carries vehicles or a plant-room floor, the two-component polyurea SealForce RC30 takes over.

Two separate warranties. Rayson warrants SealForce WB20 against manufacturing defects for three years from the date of supply, provided the material is applied per the technical data sheet and the membrane is flood-tested before it is covered; the remedy is replacement material. The applicator warrants its workmanship on its own quotation. Ask for both in writing.

An applicator in the Rayson network. Rayson manufactures and supplies the membrane and publishes its technical data; the applicator inspects the bathroom, issues the quotation and invoice, hacks, prepares, applies the membrane, flood-tests and re-tiles under its own workmanship warranty. Send us photographs of the toilet and of any stain below and we will specify the system and introduce an applicator.