Waterproofing is rarely given the scrutiny it deserves when evaluating a wall system. In Singapore’s tropical climate – frequent heavy rainfall, persistently high humidity, intense UV exposure – a wall system that performs adequately elsewhere may fail prematurely here.
This guide examines how traditional waterproofing works across concrete and brick assemblies and Inplex’s proprietary Monomer Wall System. It looks at where the waterproofing layer sits, how each system fails, and what that failure means for the building and its occupants – including where leakage problems actually originate and what questions stakeholders should be asking.
How Traditional Wall Waterproofing Works
Above-grade waterproofing in traditional wall assemblies (brick or concrete walls) is about resistance and drainage, not an impermeable barrier. Some water is allowed to seep through but the mass of the wall itself holds water until the rain stops upon which the water is allowed to slowly evaporate.
To understand how waterproofing works for a traditional wall, we need to break down the composition of these traditional wall assemblies. A concrete wall above grade has three layers: the concrete structure, cement plaster, and external paint. None of these is waterproof in isolation – they work together as a system that slows and deflects water rather than blocking it outright.
- Concrete is the structural layer. Dense, well-mixed concrete is reasonably water-resistant but not waterproof because it is porous and vulnerable at cracks and joints.
- Cement plaster fills surface voids and reduces the porosity of the concrete face. It absorbs water rather than repelling it, so its contribution is slowing penetration, not stopping it. It also cracks over time.
- External paint is the outermost and most water-active layer. Standard paint provides minimal protection, but elastomeric or waterproof paint forms a hydrophobic film that actively repels water and can bridge hairline cracks. This is the layer doing the most waterproofing work in a typical assembly.
The weak points are always cracks and joints as no paint or plaster reliably seals these without specific intervention.
A brick wall, on the other hand, works on a similar principle but with an added variable – the mortar joints. The assembly is typically: brick, mortar joints, plaster, and external paint.
- Bricks themselves are fairly dense and water-resistant, though this varies by type and firing quality.
- Mortar joints are the primary vulnerability. Mortar is more porous than brick and tends to crack and erode over time, creating the main water entry points in a brick wall.
- Plaster and paint serve the same roles as in a concrete wall – plaster fills and densifies the surface, paint repels water at the face.
A key difference from concrete is that brick walls are often designed with the assumption that some water will penetrate the outer face, and the wall cavity (in cavity wall construction) or the thickness of the wall manages that water by allowing it to drain or evaporate before it reaches the interior.
Water that hits the wall face should be repelled by the paint layer, slowed by the plaster, and what little penetrates should be able to dry out – the wall needs to breathe. This is why above-grade walls use breathable coatings rather than fully sealed membranes, which would trap moisture inside the wall and cause more damage than they prevent.
Why Traditional Wall Waterproofing Fails
The system relies on the outermost layer which is the paint remaining intact
Paint is doing the most waterproofing work, but it is also the most exposed and shortest-lived layer. UV exposure, thermal cycling, and weathering degrade it within a few years. Once the paint film breaks down, water reaches the plaster which absorbs rather than repels and penetration accelerates. The system is only as good as its maintenance cycle.
Cracks defeat the entire assembly
Every layer in both assemblies – concrete, plaster, mortar joints, brick – cracks over time due to thermal movement, structural loading, or shrinkage. This is a material reality. A crack bypasses all the resistance the intact layers provide and gives water a direct path inward. Paint and plaster cannot bridge anything beyond hairline cracks, so any meaningful crack becomes an entry point.
Joints and interfaces are inherently weak
Window frames, door frames, service penetrations, and construction joints are where different materials meet. Different materials move at different rates with temperature changes, so sealants at these interfaces fatigue and separate over time. These are statistically where most water infiltration actually occurs, not through the flat wall face.
The assembly cannot handle sustained water contact
The system is designed for rain that hits and runs off. It is not designed for water that sits, ponding at sills, blocked drainage at parapets, persistent damp from ground splash or prolonged rain with increasingly erratic weather patterns in tropical climates like Singapore. Sustained contact overwhelms the slow-resistance model and drives water through layers that would otherwise perform adequately.
Traditional wall assemblies are therefore maintenance-dependent waterproofing systems that depend on continuity where every layer is intact, every joint sealed and every crack absent.
How the Monomer Wall System Works
The Monomer Wall System is a proprietary wall assembly developed through Inplex’s in-house R&D programme. It is a sequence of increasingly targeted layers that address the limitations of the layer before it, coming together to form an integrated system with robust redundancies.
From exterior to interior, the assembly is as follows:
- External paint works in the same way as in a traditional wall assembly
- Horizontally laid cement board forms the exterior-facing substrate. Dimensionally stable and unaffected by moisture, it presents a durable exterior face that outperforms timber-based cladding systems significantly. Where boards meet, a sealant is applied at the joints to close the first potential water entry points.
- Vertically laid cement board sits directly behind, oriented perpendicular to the horizontal layer. This cross-orientation – a detail developed through Inplex’s R&D process – ensures the joints of the two layers never align, so water that finds a gap in the outer board encounters solid board behind it rather than a continuous path inward. Joints in this layer are likewise sealed, providing a second sealed barrier in a different orientation.
- Waterproof textile membrane is the primary waterproofing layer. It is installed using a proprietary overlapping sequence validated through Inplex’s research, directing any water that penetrates the cement boards downward and outward, away from the frame. The lapping method is proprietary and critical to the system’s performance.
- Light gauge steel frame is the structural core. Identifiable by its distinctive blue finish, our frame uses BlueScope’s proprietary coating technology for corrosion resistance. The frame will not shrink, twist, or warp over time, keeping the assembly dimensionally stable and preventing the gaps that progressively undermine the layers in front of it. It is the final safeguard in a system built on multiple redundant lines of defence.
Does the Monomer Wall System Perform Better in Singapore’s Climate?
The Monomer Wall System’s waterproofing is built deeper into the assembly and is less exposed to the conditions that cause degradation, making it intrinsically more suited to the tropical climate over the long term. The concrete wall can perform adequately in Singapore, but its performance degrades in direct proportion to how well external maintenance is kept up.
Singapore’s climate presents three specific stresses on wall assemblies: (i) near-constant high humidity, (ii) frequent heavy rainfall including wind-driven rain, and (iii) intense UV exposure. A wall system needs to manage all three simultaneously and do so durably over decades with minimal maintenance.
The Monomer Wall System is structurally better suited to tropical conditions for several reasons:
- Cement board does not absorb water the way plaster does, and unlike paint on a concrete wall, it does not degrade with UV exposure. The substrate itself is climate-resistant.
- Dual sealed layers mean water has to defeat two independently sealed, cross-oriented barriers before reaching the membrane – in a climate with frequent wind-driven rain, this matters.
- The waterproof textile membrane is the true waterproofing layer and is protected behind two solid boards, shielded from UV entirely. Unlike external paint, it does not degrade from sun exposure.
- LGS steel frame with BlueScope coating does not corrode, rot, or swell – failure modes that humidity accelerates in timber-framed or concrete systems.
- Maintenance burden is lower – the layers doing the waterproofing work are protected rather than exposed, so the system does not depend on the outermost layer remaining in perfect condition.
Is Traditional Waterproofing Ever the Right Choice?
A concrete wall assembly can be properly waterproofed but the system is inherently maintenance-dependent in a climate that accelerates degradation. The concrete wall’s waterproofing relies on external paint remaining intact, but elastomeric paint degrades faster under intense UV and thermal cycling. Once the paint film breaks down, the porous plaster behind it absorbs moisture readily. Singapore’s humidity means the wall never fully dries between rain events, so absorbed moisture accumulates over time. Cracks from thermal movement are also common, and in a humid climate those cracks stay wet rather than drying out.
When failures occur, they’re often difficult to diagnose and expensive to repair.
Where Do Leakage Problems Actually Start?
Leakage is bulk water finding a continuous path through the wall. It almost never starts through the flat face of an intact wall. It starts at discontinuities:
- Joints and edges – where boards meet, where the wall meets a window frame, door frame, parapet, or sill. These are interfaces between different materials moving at different rates, so sealants fatigue and open over time.
- Cracks – from thermal movement, structural settlement, or material shrinkage. A crack bypasses every intact layer and gives water a direct route inward.
- Penetrations – pipes, electrical conduits, fixing screws. Any hole through the wall assembly that is not properly sealed is a leakage point.
- Degraded surface protection – in a concrete wall, once the paint film breaks down and plaster absorbs sustained moisture, water eventually finds its way through. This is a slower process than a crack or failed joint but the same outcome.
In the Monomer Wall System, the sealed joints at both cement board layers and the waterproof textile membrane significantly reduce these risks, but the most vulnerable points remain the same: window and door reveals, penetrations, and the bottom termination edge of the membrane where it must be correctly detailed to drain outward.
To understand how design decisions impact build quality and performance, see this blog article.
What Should Stakeholders Be Asking?
For developers, architects, contractors, and homeowners, the key isn’t just choosing a waterproofing product. Instead, it’s evaluating the entire wall system.
Important questions include:
- [Performance] Where is the primary waterproofing layer, and how protected is it from the elements?
- [Performance] How are joints, penetrations, and interfaces with windows and doors detailed and sealed?
- [Performance] How does the system manage moisture vapour, not just liquid water?
- [Durability] How does the system behave as the building moves and settles over time – do joints open, do materials crack?
- [Durability] Has the system been tested or validated in high-humidity, high-rainfall climates comparable to Singapore?
- [Failure consequences] How easy is it to locate the source of a leak once water ingress is detected?
- [Failure consequences] Is the waterproofing layer accessible for inspection and repair, or is it concealed behind other layers?
- [Maintenance burden] Which layers require active maintenance to sustain waterproofing performance, and how frequently?
- [Maintenance burden] Does the manufacturer or contractor provide a warranty on the waterproofing system, and under what conditions does it apply?
These questions shift the conversation from short-term compliance to long-term performance.
Conclusion
Waterproofing failures do not occur through intact wall faces. They occur at joints, cracks, and penetrations where continuity breaks down, compounded by conditions that accelerate degradation and prevent walls from drying out.
Traditional assemblies concentrate waterproofing at the outermost, most exposed layers – paint and plaster – which degrade with UV and weathering and depend on regular maintenance to remain effective.
The Monomer Wall System positions its primary waterproofing layer deep within the assembly, protected behind two independently sealed, cross-oriented cement board layers. The layers doing the most critical work are the least exposed to the conditions that cause failure. In Singapore’s climate, that distinction compounds significantly over the lifetime of a building. Learn more or get in touch with us.
