Waterproofing is not one product. It is a category containing several quite different systems, and the most common cause of failure is not bad workmanship, it is the wrong system specified for the substrate and exposure in the first place.

Torch-on membrane

Sheets of bituminous membrane heat-welded to the substrate with a torch. Robust, thick, and forgiving of minor substrate movement. It is the usual choice for flat roofs and large podium decks.

Its weakness is detail work. Around drains, upstands and pipe penetrations the sheet has to be cut and lapped, and those laps are where nearly every torch-on failure starts. It also needs a protective screed or covering, left exposed to Singapore UV it degrades faster than the datasheet suggests.

Liquid-applied membrane

Polyurethane or acrylic applied by roller or spray, curing into a seamless film. Because there are no joints, it handles complex shapes, balconies, planters, bathrooms, anything with a lot of corners and penetrations, far better than sheet systems.

The tradeoff is that film thickness depends entirely on the applicator. Too thin and it will not perform, and you cannot tell by looking. This is a system where who applies it matters as much as what is applied.

Cementitious coatings

Cement-based slurries that bond to concrete and masonry. Cheap, easy to apply, and tolerant of damp substrates, which makes them common for water tanks, basements and internal wet areas.

They are rigid, though. Any structural movement or crack in the substrate transfers straight through, so they are a poor choice anywhere that flexes or is exposed to thermal cycling.

Injection grouting

Resin or grout injected under pressure into an existing crack. A repair technique rather than a waterproofing system, useful for stopping an active leak through a structural crack, not for protecting a surface.

What actually determines the choice

  • What the substrate is, and whether it moves
  • Whether the surface will be walked on, planted on, or left alone
  • Whether it will be exposed to UV or covered by screed or tiles
  • How much standing water it needs to tolerate, and for how long
  • Whether you can take the area out of service long enough for proper curing

Any contractor quoting a waterproofing job should tell you which system they are proposing and why that one. If the quotation just says "waterproofing" with a price, you do not yet have enough information to compare it against anything.