Web Menu

Product Search

Language

Share

Waterproof Mortar Additives

-- Steady & Reliable Manufacturer --

Introduction

Waterproof mortar additives are functional polymer and cellulosic admixtures that improve the water impermeability, crack resistance, and substrate adhesion of cement-based waterproofing systems used in wet rooms, basements, swimming pools, balconies, and water infrastructure. The term encompasses both flexible polymer-modified waterproofing mortars (Type II slurries) and rigid cementitious coatings (Type I), each requiring a distinct additive profile.

Redispersible polymer powder (RDP) is the key performance additive in waterproof mortars — at dosages of 3–8%, it creates a continuous polymer film within the cured cement matrix that dramatically reduces capillary water absorption and bridges minor cracks. HPMC at 0.2–0.4% supports workability and water retention during application. The combination of high RDP content and precisely specified HPMC is what distinguishes a professionally performing waterproof mortar from a basic cement slurry.

Specification

Parameter HPMC (Waterproofing Grade) RDP — Flexible (Type II) RDP — Rigid (Type I)
Viscosity (2%, 20°C) 50,000–150,000 mPa·s N/A N/A
Dosage (%) 0.2–0.4 4.0–8.0 1.5–3.0
Polymer type — VAE or VAE-VeoVa VAE or Acrylic
MFT (°C) — ≤5 (flexible) 0–10 (rigid)
Tg (°C) — -15 to -5 (flexible) -5 to +10 (rigid)
Crack-bridging ability — ≥0.5 mm (flexible type) ≤0.1 mm (rigid type)
Water absorption reduction — >80% vs unmodified >50% vs unmodified
Ash content (%) ≤5 ≤10 ≤10
Moisture (%) ≤5 ≤2 ≤2

Type II flexible waterproofing mortar (high RDP, low Tg polymer) is required for any substrate subject to movement: balconies, podium decks, swimming pool shells, and building expansion zone areas.

Application

  • Wet room and bathroom waterproofing (Type II): Two-coat flexible mortar system using RDP at 5–7% and HPMC at 0.25–0.35%; applied at 1.5–2.0 mm per coat to walls and floors before tile installation.
  • Basement tanking (positive side, Type I): Rigid waterproof mortar with RDP at 2–3% and HPMC at 0.2–0.3%; applied in 2–3 coats to interior basement walls to resist hydrostatic water pressure.
  • Swimming pool shell waterproofing: Flexible Type II system with high crack-bridging RDP (≥0.5 mm) applied over concrete pool shells that experience seasonal thermal movement and water pressure cycling.
  • Balcony and podium deck waterproofing: Flexible waterproof mortar (RDP 6–8%) applied beneath tile or paving on elevated slabs subject to thermal cycling and dynamic loading from foot traffic.
  • Water infrastructure linings (tanks, channels): Rigid or semi-flexible waterproof mortar with RDP and HPMC applied as protective lining in potable water storage tanks and irrigation channels — food-safe grades available.
  • Bridge deck and parking structure waterproofing: High-RDP content flexible mortar with additional crystalline waterproofing compound used under asphalt or resin topping on concrete decks.

Advantage

  • Crack-bridging for long-term watertightness: Flexible-grade RDP (low Tg, -15 to -5°C) produces a rubbery polymer network within the cured mortar that bridges cracks up to 0.5 mm width — preventing water ingress through the micro-cracking that inevitably occurs in cementitious substrates over their service life.
  • Capillary water absorption reduced by >80%: RDP-modified waterproof mortar at 5–7% dosage consistently achieves water absorption values of 0.05–0.15 kg/(m²·h^0.5) by the Karsten tube method — compared to 0.5–1.0 kg/(m²·h^0.5) for unmodified cement mortar.
  • Adhesion to non-porous substrates: HPMC + RDP combination provides ≥1.0 N/mm² pull-off adhesion to smooth concrete, existing tile, and coated surfaces without primer — critical for renovation waterproofing projects.
  • Positive and negative water pressure resistance: Properly cured rigid waterproof mortar (Type I) can resist positive water pressure of 3–5 bar (30–50 m head) — sufficient for most basement tanking applications without cavitation membrane.
  • Substrate movement tolerance: Type II flexible systems (RDP ≥5%, low Tg) accommodate substrate movement of ±1.5–2.5 mm without cracking, making them appropriate for concrete structures with anticipated live load deflection or thermal cycling.
  • Potable water safe grades available: Our RDP grades for water infrastructure lining applications are available with NSF/ANSI 61 or equivalent potable water contact certification, supporting use in drinking water storage tanks and channel linings.
  • Q: What is the difference between Type I and Type II waterproof mortar, and which RDP grade do I need for each?
  • A: Type I (rigid) waterproof mortar uses RDP at 1.5–3.0% to reduce water absorption and improve surface cohesion without requiring significant flexibility. It is suited for stable substrates like basement walls with no structural movement. Type II (flexible) waterproof mortar uses RDP at 4–8% with a low glass transition temperature (Tg -15 to -5°C) to provide crack-bridging of ≥0.5 mm and accommodate substrate movement. For balconies, pool shells, and any elevated or moving structure, Type II is required. We supply both RDP grades and can advise based on your specific application and movement expectation.
  • Q: How many coats of waterproof mortar are needed for a wet room floor and walls?
  • A: Standard practice for wet room and bathroom waterproofing is two coats of flexible Type II mortar: first coat 1.0–1.5 mm applied after surface priming; second coat 1.0–1.5 mm applied after the first coat has dried to touch (typically 2–4 hours at 20°C). Total dry-film thickness of 1.5–2.0 mm is the industry minimum for EN 14891 Class I certified systems. Higher risk areas (shower cubicle walls, floor drain surrounds) should receive a third coat or fabric reinforcement embedding in the first coat.
  • Q: Can waterproof mortar be applied directly to painted concrete walls?
  • A: Adhesion to painted surfaces is technically possible with HPMC + RDP formulations achieving ≥0.5 N/mm² pull-off strength on well-bonded paint layers. However, the limiting factor is always the bond between the existing paint and the substrate, not the waterproof mortar itself. Where paint adhesion is uncertain, it is always more reliable to mechanically remove the paint or use a bonding primer before applying the waterproof mortar system. We recommend pull-off adhesion testing on a trial area before full application.
  • Q: Do you supply RDP grades suitable for potable water contact applications?
  • A: Yes. We stock RDP grades produced in compliance with NSF/ANSI 61 (North America) and relevant European drinking water contact regulations (e.g., KTW-BWGL in Germany, ACS in France). These grades are suitable for use in mortars lining potable water storage tanks, treatment plant channels, and drinking water infrastructure. Please specify the target certification standard when requesting samples or placing orders so we can supply the correct documented grade.
  • Q: What causes blistering or delamination of waterproof mortar, and how can additives help prevent it?
  • A: Blistering and delamination in waterproof mortar are most commonly caused by (1) insufficient substrate preparation, (2) applying mortar over a substrate with active moisture migration, or (3) applying the second coat before the first coat has sufficiently dried. The RDP in the formulation forms a vapor-impermeable film on curing, which can trap moisture if the substrate is wet or if application intervals are not respected. HPMC improves adhesion at the mortar-substrate interface and helps manage water retention during application to reduce these risks. Always verify substrate moisture content (typically <4% by weight) before application.
About Us
Zhejiang Yisheng New Material Co., Ltd.
Zhejiang Yisheng New Material Co., Ltd. is a professional enterprise engaged in the design, development, manufacturing, application, and sales of cellulose ether, located in the Shangyu Economic and Technological Development Zone, part of the Hangzhou Bay National Industrial Park. With a core concept of safety, environmental protection, and sustainable development, the company boasts an annual production capacity of 15,000 tons of cellulose ether, offering a complete range of products including HEC (hydroxyethylcellulose), HEMC (hydroxyethyl methylcellulose), and HPMC (hydroxypropyl methylcellulose). Our products serve various sectors such as oil fields, coatings, dry powder mortar, cosmetics, personal care products, medicine, and many others. Yisheng has a global presence, providing stable cellulose ethers and services to customers worldwide.
As a professional China Waterproof Mortar Additives Supplier and Waterproof Mortar Additives Company, The company adheres to the principles of safety and environmental protection as the foundation of its development. It implements and further consolidates safety and environmental protection measures, striving to create green and environmentally friendly production processes, safe and effective control systems, and orderly production management. This approach lays a solid foundation for the company's sustainable development. Yisheng boasts a scientific management mechanism, a comprehensive quality management system, stringent product testing methods, advanced technology, state-of-the-art equipment, and high-quality after-sales service.
Zhejiang Yisheng New Material Co., Ltd.

+86-18067879812
Zhejiang Yisheng New Material Co., Ltd.

sarah@ys-cellulose.com
Zhejiang Yisheng New Material Co., Ltd.