Abstract

This paper classifies waterproofing forms into jointed waterproofing and seamless waterproofing based on the presence or absence of water-permeable pores in the waterproofing layer. In practical design, the selection of jointed or seamless waterproofing according to specific project conditions is crucial for improving the quality of building waterproofing.

Keywords: Jointed Waterproofing; Seamless Waterproofing; Waterproofing Forms; Waterproofing Design

1 Introduction

There are over 5 major categories, 19 subcategories, and more than 80 varieties of waterproofing materials in China¹. Some argue that there are hundreds of varieties, with results varying due to different statistical methods. Nevertheless, it is evident that China's waterproofing materials present a pattern of multiple varieties and grades.

Despite the wide variety, current roof waterproofing materials in China are mainly divided into two categories: inorganic and organic. The former is represented by waterproof mortar, waterproof concrete, clay tiles, and cement tiles; the latter is represented by organic waterproof coatings and waterproofing membranes.

2 Main Forms of Waterproofing

2.1 Classification by Waterproofing Mechanism

Based on the waterproofing mechanism, the main forms are dense waterproofing, membrane waterproofing, and hydrophobic waterproofing.

Dense Waterproofing: Waterproof mortar, waterproof concrete, and cement-based waterproof coatings primarily achieve waterproofing by increasing their own density and thickness, which determine their performance.
Membrane Waterproofing: Waterproof coatings and membranes form a continuous waterproof film on the building surface to block water.
Hydrophobic Waterproofing: Hydrophobic materials (e.g., silicone water repellents) alter the surface wettability to repel water.

Among these, hydrophobic waterproofing is not a primary form because the thin hydrophobic layer cannot resist pressurized water and has poor durability (losing effectiveness in about one year). Thus, dense and membrane waterproofing are the dominant forms in China.

2.2 Classification by Presence of Joints

This paper classifies waterproofing forms into jointed waterproofing and seamless waterproofing based on the integrity of the waterproofing layer.

2.2.1 Definition

Jointed Waterproofing: Refers to systems that (1) inherently contain micro-pores or cracks; (2) cannot ensure effective sealing of pores/cracks due to construction methods; or (3) are prone to failure under long-term water immersion despite having no initial cracks. It includes waterproof mortar, concrete, cement-based coatings, water-based coatings, improperly sealed membrane systems, and various tiles.
Seamless Waterproofing: Refers to systems constructed to be free of water-permeable pores or joints. It includes reaction-cured and solvent-based organic coatings, as well as fully sealed membrane systems with reliable joints and terminations.

Key Differences:

Jointed systems have inherent permeable paths, while seamless systems do not.
Seamless systems are less affected by construction conditions and can ensure integrity across different regions, projects, and contractors.

2.2.2 Waterproof Mortar and Concrete are Jointed Waterproofing

American scholars consider pores ≥100 nm as critical for permeability. Chinese scholars classify concrete pores as harmless (2.5–20 nm), less harmful (20–50 nm), harmful (50–200 nm), and severely harmful (200 nm–11 μm). These data show that water-permeable pores in concrete are nanoscale and invisible to the naked eye.

Ordinary mortar/concrete contains not only inherent pores but also construction and expansion joints. Furthermore, cracks inevitably develop during service. As one scholar noted²: 'A flawless structure is an ideal; the real world has flaws. We can never defeat, eliminate, or eradicate cracks—only control them, allowing harmless ones and minimizing harmful ones. Cracks are not just defects; they are a physical property of concrete.'

Even with waterproofing admixtures, mortar and concrete cannot guarantee 100% leak-tightness due to material limitations, environment, and workmanship. Therefore, they are classified as jointed waterproofing.

2.2.3 Cement-based Coatings, Water-based Coatings, and Tiles are Jointed Waterproofing

Cement-based coatings inherit the properties of mortar/concrete and are thus jointed.
Water-based coatings contain emulsifiers that easily swell under long-term water exposure, making them jointed.
Tiles have large gaps between units and are therefore jointed.

2.2.4 Most Membrane Systems are Jointed Waterproofing

Flat roofs account for approximately 70% of urban construction in China³, and membranes constitute about 65% of total waterproofing materials. Most membrane systems are jointed for four main reasons:

Permeable joints exist between membranes, at membrane-to-component interfaces, and at wall terminations.
Manufacturers often supply only base materials without a complete system, leaving joints poorly sealed.
Most construction workers are migrant laborers with limited education and training, making perfect sealing difficult.
Micro-cracks are invisible; even careful work cannot guarantee 100% sealing.

Despite extensive R&D to convert jointed systems to seamless, most applications remain jointed.

2.2.5 Reaction-Cured Coatings, Solvent-Based Coatings, and Integrated Membrane Systems are Seamless Waterproofing

Reaction-cured and solvent-based organic coatings form a seamless film and can withstand long-term immersion, thus being seamless.
Integrated membrane systems, equipped with proper sealants, adhesives, and fasteners to reliably seal joints and secure terminations, are also classified as seamless.

Seamless systems demand high compatibility of materials and skilled workmanship, and few membrane products meet these standards.

3 Waterproofing Forms and Design

Leakage depends on four factors:

Jointed layer: Inherent permeable paths.
Water source: Presence of water on the layer surface.
Duration: Longer exposure increases leakage.
Pressure: Higher pressure increases leakage.

The first two are necessary conditions; without either, no leakage occurs. The other three determine leakage volume proportionally.

3.1 Seamless Waterproofing is Mandatory for 'Prevention-Focused' Projects

Projects with standing water, poor drainage, or water accumulation require seamless waterproofing to ensure quality. These include:

Water-retaining structures: Fire tanks, swimming pools, baths, rainwater harvesting tanks, and green roofs.
Underground structures: Subways, basements, and tunnels.
Water-prone areas: Roofs with 2–5% slope, roofs with rigid over-layers, concrete pavers, accessible roofs, inverted roofs, garden roofs, bathrooms, and insulated/exterior-clad walls.

3.2 Jointed or Seamless Waterproofing is Suitable for 'Drainage-Focused' Projects

If water drains rapidly, jointed systems may suffice. These include:

Roofs with slope ≥5% using exposed membranes or raised pavers.
Sloped roofs.
Walls (e.g., tile-clad parapets in some Qingdao buildings).

Note: When using jointed systems, strictly follow the overlapping-downwater principle and provide detailed design and dedicated materials for critical details.

4 Conclusion

Most projects require seamless waterproofing, driving the development of high-performance coatings and integrated membrane systems. Given environmental concerns, priority should be given to reaction-cured coatings (e.g., polyurethane, polyurea) and fully sealed membrane systems with complete accessories.

Regrettably, most current applications in China are jointed due to incomplete systems or poor accessory quality. We must face this reality and select appropriate forms and materials based on project conditions. Statistics from real estate developers show a leakage rate of approximately 65%, largely due to the failure to distinguish between jointed and seamless systems, leading to blind design and construction.

Seam waterproofing and seamless waterproofing