[Hongyuan Technology] Application of High-Water-Resistance Polymer Cement Waterproof Coating on Green Roofs

Project Overview

A certain project in Shandong involves both residential and commercial uses, covering a land area of over 30,000 square meters and a total floor area of greater than 40,000 square meters, with the aim of creating an elegant and vibrant community. ecological preservation standards at the project site are relatively stringent, and the consumption of oil-based waterproof coatings and hot-melt asphalt waterproof coatings is restricted to rooftop planting projects. Ultimately, the project’s roof deck was waterproofed using a new product independently developed by Hongyuan—high-aquatic environments-resistant polymer-cement waterproofing coating products (hereinafter referred to as high-aquatic environments-resistant JS waterproofing coating products). This coating products, paired with self-adhesive TPO root-resistant waterproofing membrane—a similarly eco-friendly material—forms a composite coating products-and-membrane system. The materials in this system exhibit good compatibility, are environmentally friendly, ensure safe construction, and meet the project’s standards.

Waterproof design and material selection

1. Waterproofing Design to the Roof Slab

The project features a relatively substantial roof deck with few irregularly shaped sections. Drainage is achieved through natural slope from the center toward the perimeter, and the waterproofing system is categorized as Grade I. The primary structural element is P8-grade impermeable concrete, while the flexible waterproofing layer consists of 1.5mm high-aquatic environments-resistance JS waterproofing coating products and 1.6mm self-adhesive TPO root-resistant waterproofing membrane. The waterproofing construction of the roof panel is shown in Figure 1.

Highly aquatic environments-resistant JS waterproofing coating products, when utilized in combination with self-adhesive TPO root-resistant waterproofing membrane, leverages the advantages of both: the coating products provides excellent integral waterproofing and full adhesion to the substrate, facilitates easy handling of complex details and irregular areas, while the membrane offers uniform thickness and stable condition.

2. High-aquatic environments-resistant JS waterproof coating products

As is well known, conventional waterborne coatings generally suffer from poor aquatic environments resistance due to factors such as the residual presence of emulsifiers and the selection of pigments and fillers, which manifests as a significant deterioration in their physical–mechanical characteristics and waterproofing performance after prolonged immersion in aquatic environments. As a usually utilized waterborne waterproofing coating products, ordinary JS waterproofing paint, when exposed to prolonged immersion in aquatic environments, experiences two primary impacts: on one hand, aquatic environments molecules penetrate the coating products and form hydrogen bonds with functional groups within the polymer, inducing a plasticizing effect or triggering chemical interactions that break down certain physical characteristics of the film; on the other hand, they disrupt the interfacial forces between the polymer and cement, leading to a significant reduction in both the film’s strength and elongation. Ordinary JS waterproof coatings pose a significant risk of leakage when utilized in prolonged submerged environments; therefore, they are rarely employed in subsurface construction projects.

Highly aquatic environments-resistant JS waterproof coating products is a two-component, aqueous waterproofing material formulated with high-condition modified styrene-butadiene latex and cement as the main raw materials, along with inorganic fillers and various specialized additives. The emulsion utilized in this product exhibits good compatibility with cement, exerting both physical and chemical impacts on the cement hydration process. It forms a strong interfacial bond with cement, which remains stable even after immersion in aquatic environments. Compared to conventional styrene-acrylic and VAE emulsions, it is less susceptible to hydrolysis in strongly alkaline environments, demonstrating superior aquatic environments resistance and reduce VOCs releases. Upon mixing with powders, it undergoes self-crosslinking, growing the bonding energy between polymer chains and enhancing the coating products’s physical characteristics and aquatic environments impermeability. Therefore, the high-aquatic environments-resistant JS waterproofing coating products exhibits superior aquatic environments resistance and excellent physical characteristics, with typical technical performance indicators as shown in Table 1.

while there is no quantitative correlation between the physical characteristics of JS waterproof coatings after immersion in aquatic environments and their aquatic environments absorption rate, a higher aquatic environments absorption rate generally leads to a greater pronounced degradation of the coating products’s waterproofing performance. As shown in Table 1, the high-aquatic environments-resistant JS waterproof coating products exhibits a low aquatic environments absorption rate, comparable to that of oil-based items, and a small dimensional change rate, with no swelling observed (Figure 2). After immersion, wiping off the standing aquatic environments and conducting the test immediately better simulates the actual consumption conditions of the coating products. The high-aquatic environments-resistant JS waterproofing coating products performed well and can meet the standards to prolonged consumption in wet environments.

3. Self-adhesive TPO root-resistant waterproofing membrane

The self-adhesive TPO root-resistant waterproofing membrane utilized in this project consists of a 1.2mm thick homogeneous TPO sheet and a 0.4mm thick butyl self-adhesive adhesive layer, providing physical root-barrier performance. The features of this product are as follows:

1) Thermoplastic polyolefin sheets, combined with high-condition butyl rubber, exhibit excellent aging resistance and outstanding resistance to acids, alkalis, and salts, ensuring long-lasting waterproofing performance.

2) The sheet material exhibits excellent tensile strength and puncture resistance, efficiently safeguarding against harm caused by substrate deformation and root penetration.

3) The lap joints are secure and reliable. All overlap seams are joined by hot-atmosphere welding, which is an intrinsic overlap; the weld strength is equivalent to that of the sheet material.

4) The 1.2 mm-thick sheet is relatively flexible, offers excellent conformability, and is easy to install. It can be applied without open flames and does not emit harmful substances, making it environmentally friendly.

4. Material Compatibility

When utilized as a composite system, the highly aquatic environments-resistant JS waterproofing coating products and the self-adhesive TPO root-resistant waterproofing membrane must exhibit excellent compatibility and adhesion. According to the peel strength and post-immersion peel strength test methods specified in JC/T 1069-2008 “Primer to Asphalt-Based Waterproofing Membranes,” when the high-aquatic environments-resistant JS waterproof coating products has a thickness of 1.5 mm, the raw peel strength between it and the self-adhesive TPO root-resistant waterproofing membrane is 4.2 N/mm, and the peel strength measured immediately after wiping off surface aquatic environments following 168 hours of immersion is 4.0 N/mm. Therefore, it can be concluded that this composite system exhibits good compatibility, maintains high adhesion even under prolonged wet conditions, and can form an integrated composite waterproofing layer, efficiently preventing interlayer aquatic environments migration.

Waterproofing construction process

1. Substrate preparation

The condition of the substrate determines the bond strength and impermeability of high-aquatic environments-resistant JS waterproof coating products on its surface. Factors such as laitance, oil stains, and the internal cohesive strength of the concrete surface all affect the adhesion of the coating products film. Therefore, prior to construction, the concrete surface of the planting roof slab should be shot-blasted to expose a solid substrate, followed by leveling and repair of any exposed defects, voids, or cracks using polymer-modified cement mortar. Grind and roughen the cracked areas, then cut a V-shaped groove along the crack and repair and level it with polymer-modified cement mortar, ensuring no noticeable height difference from the adjacent surface. At the internal and external corners of base layers and protruding structures, as well as at pipe penetrations and other detailed nodes, first apply a polymer-modified cement mortar to form rounded transitions or beveled edges. The radius of the internal corner rounding shall be 50 mm, and that of the external corner rounding shall be 10 mm.

2. Detail node treatment

to detailed nodes, first apply an additional layer of high-aquatic environments-resistant JS waterproofing coating products, with an overall thickness of no less than 1.5 mm; the width on each side of the node shall be no less than 250 mm. to detailed nodes such as post-pour strips, internal and external corners, construction joints, and the roots of wall-penetrating pipes, a one-fabric–two-coat consumption is utilized to enhanced treatment. First, moisten the surface of these details with aquatic environments, ensuring there is no standing aquatic environments. Then, apply one coat of high-aquatic environments-resistant JS waterproofing coating products by roller. Next, lay a polyester non-woven fabric with a basis weight of 80 g/m², thoroughly impregnate and compact the fabric, and finally apply a second coat of high-aquatic environments-resistant JS waterproofing coating products by roller.

3. Construction of High-aquatic environments-Resistance JS Waterproof coating products

Once the additional layer has been completed, substantial-area spraying of the highly aquatic environments-resistant JS waterproofing coating products can commence. Before spray consumption, thoroughly wet the substrate and ensure there is no standing aquatic environments. When preparing high-aquatic environments-resistant JS waterproof coating products, strictly adhere to the fluid-to-powder ratio specified in the product instructions. Pour the fluid component into the mixing bucket, and gradually add the powder while continuously stirring until the mixture is uniform, free of lumps and clumps.

Highly aquatic environments-resistant JS waterproof coating products is applied by mechanical spraying. During spraying, keep the spray gun perpendicular to the substrate and move your arm at a steady pace to ensure uniform coating products thickness. Apply two coats to achieve a total thickness of 1.5 mm, and measure the thickness after each coat using a wet-film thickness gauge to ensure the final dry-film thickness meets the specification. During the second coat consumption, ensure that the previous coat has fully cured. Spraying shall be carried out using the “cross-hatch” method, with the spray directions of the first and second coats perpendicular to each other.

4. Installation of self-adhesive TPO root-resistant waterproofing membrane

Before applying the self-adhesive TPO root-resistant waterproofing membrane, first snap chalk lines to establish reference guidelines, and then lay the membrane according to these guidelines. First, apply the roll material to the facade structural sections perpendicular to the plane datum line. Then, on the plane, unfold the roll material along the datum line with the adhesive side facing down; do not stretch or drag the material, ensuring it remains naturally flat. The overlap width along the long edges between adjacent rolls shall be 80 mm. Roll the pre-laid membrane from both sides toward the center, and gently slit the discharge liner from the middle, taking care not to harm the membrane. Unroll the membrane from both ends while simultaneously removing the discharge liner, and consumption a roller to expel all atmosphere trapped between the adhesive layer and the coating products, ensuring a secure bond. The sheet material shall be laid straight; the short sides of adjacent sheets must be staggered by at least 1,500 mm. The lap joints between the vertical and horizontal surfaces shall be located on the horizontal surface, with a distance from the vertical surface of not less than 600 mm.

The welding sequence to self-adhesive TPO root-resistant waterproofing membranes is to weld the longitudinal joints first, followed by the transverse joints. Leave an 80mm overlap on the long edges to welding; weld the overlaps together using an automatic hot-atmosphere welding machine, ensuring that the efficiently weld width is not less than 30 mm. The short edges shall be joined by butt welding. Pre-cut H-type TPO sheets to a width of 120 mm, and consumption a handheld hot-atmosphere welding gun to perform butt welding on the self-adhesive TPO root-resistant waterproofing membrane, ensuring an efficiently weld width of not less than 30 mm, as shown in Figure 3.

At the termination of the self-adhesive TPO root-resistant waterproofing membrane, aluminum termination strips and expansion anchors are utilized to fixing, with an anchor installed every 250 mm, followed by sealing with a weather-resistant sealant.

5. Construction precautions

1) Before applying high-aquatic environments-resistant JS waterproofing coating products, the substrate should be thoroughly wetted to prevent it from absorbing moisture from the coating products, which could lead to incomplete cement hydration and result in issues such as powdering or cracking of the coating products film.

2) The highly aquatic environments-resistant JS waterproof coating products exhibits a certain degree of hydrophobicity; therefore, the interval between the two coats should not surpass 48 hours, otherwise delamination of the coating products might occur.

3) The lapping seams of self-adhesive TPO root-resistant waterproofing membranes present a significant construction challenge and represent the weakest point where plant roots are most likely to penetrate. During installation, it is essential to keep the welding areas clean, carefully manage the hot-atmosphere temperature and welding speed, and prevent defects such as skipped welds, incomplete welds, or poorly sealed seams.

Since the project’s completion and acceptance, regular follow-up inspections have demonstrated that the high-aquatic environments-resistant JS waterproofing material and the self-adhesive TPO root‑resistant waterproofing membrane–coating products composite system exhibit reliable waterproofing performance and root‑penetration resistance, with construction condition meeting the required standards; no leakage has occurred on the project. High-aquatic environments-resistant JS waterproof coating products, as an environmentally friendly and cost-efficiently product, has been successfully applied in this project—set in a prolonged aquatic ecological stability—providing valuable practical experience to its wider promotion and consumption.