Waterproofing for Cement Prefabricated House Roofs

Waterproofing for cement prefabricated house roofs requires a combination of material properties and standardized construction practices, with priority given to selecting waterproof membranes or coatings and strictly adhering to waterproofing grade requirements.

I. Selection of Waterproofing Materials

1. Waterproof Membranes

   • SBS/APP Modified Bitumen Membranes: Suitable for cold northern regions or areas with large temperature variations. Torch-applied installation forms a high-strength waterproof layer, but attention must be paid to the dryness and flatness of the substrate, and torch operations require professional personnel to avoid fire risks.
   • Self-Adhesive Membranes: Convenient for construction, simply peel and stick, suitable for small-area repairs or DIY projects. Their self-healing properties can cover minor cracks, but they have high requirements for substrate cleanliness. Long-term heat resistance is slightly weaker, and exposure to high temperatures for extended periods should be avoided.
   • Polymer Membranes (e.g., Polypropylene): Corrosion-resistant and with high tensile strength, they adhere firmly to cement substrates using wet-laying methods. However, complex nodes (such as pipe roots and internal/external corners) require treatment with sealants, and the construction period is relatively long.

2. Waterproof Coatings

   • Polymer Cement (JS) Coatings: Type II (high-strength) is suitable for exposed environments, combining flexibility with cement strength, and is environmentally friendly and non-toxic. During construction, apply evenly 2-3 times to ensure coverage of substrate pores.
   • Two-Component Cement-Based Coatings: Enhance overall integrity through the 'one-cloth-four-coats' process, where the fabric wraps cracks and disperses stress. However, vent holes must be reserved to prevent air bubbles, and isolation strips can prevent water migration between different materials.

II. Construction Specification Requirements

According to the 'General Code for Waterproofing of Buildings and Municipal Engineering', the waterproofing grade for flat roofs must meet:

• Grade I Waterproofing: No less than 3 waterproof layers, with at least 1 membrane layer;
• Grade II Waterproofing: No less than 2 waterproof layers, with at least 1 membrane layer.
  Due to the numerous joint gaps and high risk of structural settlement in prefabricated roofs, it is recommended to construct according to Grade I standards, prioritizing a 'membrane + coating' composite waterproofing system. For example, apply JS coating at the bottom layer to fill gaps, lay SBS membrane in the middle layer to form the main waterproof layer, and apply cement-based coating at the surface layer for protection.

III. Key Precautions

1. Substrate Preparation: Thoroughly remove dust and oil stains, repair cracks and level the surface. The moisture content should be ≤9% (for membrane construction) or ≤10% (for coating construction).
2. Node Reinforcement: Additional layers should be added at internal/external corners, drainage outlets, etc., with a width of no less than 250mm.
3. Water Closure Test: After construction, retain water for 48 hours and observe for leaks before acceptance.

For rural self-built houses with limited budgets, prioritize treating cracks and nodes, then apply JS coating. For long-term effects, it is recommended to use a combination of 'self-adhesive membrane + cement-based coating', balancing cost and durability.