9 March 2022 - 17:30, by , in PU Injection, No comments


The building that was affected by the ingress of water is partially underground in a hilly area of Singapore and was originally a garage that has since been converted into a storage room with adjoining bedrooms.

During prolonged or heavy rain events, buildings cut into hillsides are at a greater risk of being affected by natural water paths, saturated soil, elevated water tables, and hydrostatic pressure. Water must be directed away from basement walls and foundations in order to avoid water accumulating around the building. The water will eventually find its way into joints and cracks in the concrete or masonry if it is allowed to pool.


Previous contractors had installed an Ag pipe in a boxed-in area beneath the house to drain the water that was building up underneath the house. The Ag line runs through the corner of one of the bedrooms and this created a new problem because water from under the house eventually flooded the bedroom via the Ag pipe.

To prevent water from entering your house through the perforations in the Ag pipes, only solid pipes should be installed under your home. AGR pipes should not be installed INSIDE or UNDER your home.

In the section of the pipe that is inside the house, a solid PVC pipe should have been used if it was not possible to redirect the water with an Ag line around the building.


Ag pipe up close. Before rectified by plumber

Image: The pipe you can see in this photo is an ag pipe that runs through the corner of one of the bedrooms. A slotted/perforated PVC pipe is designed to sit in the soil and redirect water to improve the subsoil drainage. Ag pipes should not be installed under or inside your house.




  • Plumber to install a correct drainage system
  • Leak sealing injection and installation of reverse side membrane


A reputable plumber rectified the issue by providing an appropriate solution to redirect water that builds up under the house. Once the plumber had completed his work and the new concrete in the corner had cured, Singapore Waterproofing carried out leak sealing injections into the identified areas of water ingress followed by the application of two thick coats of cementitious negative side membrane (NSM) on top of a priming coat.




Leak sealing injection of floor/wall joint: Our leak sealing specialist intersected the joint at intervals and injected a flexible polyurethane at high pressure into the joint. After allowing the polyurethane to react and bind with any water present in the joint and surrounding concrete to form a flexible seal, the injection ports were removed, and holes filled with a suitable concrete repair material.


Polyurethane Concrete Crack Injections step by step.

Polyurethane leak sealing injection into cracked concrete step by step.






To seal leaks, water-reactive polyurethane (resin) is injected high-pressure into targeted areas to form a durable seal. A long-lasting waterproof seal is ideal to prevent the passage of water or other liquids through gaps, cracks, joints, and penetrations – typically in concrete and masonry constructions.

An experienced operator is needed for this highly specialized process. At Singapore Waterproofing, our technicians perform polyurethane injection works frequently. Our technicians receive ongoing training from industry leaders, which helps them develop expert skills.

As our primary injection resin, we use the best polyurethane (PU) product available. It has excellent performance properties. Among its main features are perpetual flexibility; very low shrinkage; water potable; low viscosity; and a hydrophilic reaction – the same product that is pre-approved by major traffic authorities around the world for major infrastructure assets.

This system can be installed in any weather – in fact,  the wetter the better, as it reacts with water right before your eyes. In dry weather, flooding the source of water entry (where possible) may have a similar effect.

Singapore Waterproofing’ proprietary injection system exceeds the highest injection process and safety standards in Australia and internationally throughout Europe and the USA.

We continually review and reassess the method, always striving to hone and improve our systems. Our proprietary leak sealing system forms a long-lasting flexible seal against water ingress which also withstands normal building movement between construction elements and details.



Our waterproof membrane (NSM 100+) is a two-component acrylic modified cementitious coating that is flexible so that it can handle a small amount of movement.

This membrane is a hardwearing, seamless waterproofing membrane for effective concrete protection. It also provides an effective barrier to waterborne salts and atmospheric gases.

The NSM 100+ system is breathable. Whilst repelling water, it allows moisture to pass through it slowly as a vapour, allowing the substrate to breathe.

It is water-based, so any vapours are non-toxic and ideal for potable water usage and it can be painted over in water-based breathable paints (e.g. low sheen or matt acrylics) and most water-based after-trades such as direct stick, tiles or render.



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