Methods for Waterproof Membrane Installation: Hot Melt, Hot Adhesive, Self-adhesive, Flooded, Pre-adhesive

According to China's construction waterproofing materials product structure statistics, waterproof membranes account for over 60%, making them the primary material in waterproofing projects. However, even high-quality waterproof membranes can fail due to improper installation, leading to leakage and loss of effectiveness. Therefore, proper installation techniques are critical. Common methods include hot melt, hot adhesive, self-adhesive, flooded, and pre-adhesive application.

Hot Melt Method

The hot melt method refers to a construction technique where a hot-melt type waterproof membrane base layer is heated using a torch to melt the adhesive layer, enabling bonding through fusion.

1. Base Layer Preparation: Clean the surface thoroughly. The base layer should be solid, flat, and dry. Apply a uniform coat of primer to the base layer, ensuring no bare spots or leaks. The surface must be dry before applying the membrane.

2. Additional Layer Work: Treat areas such as corners, pipe penetrations, joints, and expansion joints by applying additional reinforcement layers. Cut the membrane into suitable sizes and shapes beforehand, then apply it directly onto the base layer.

3. Large-Scale Application: Open and release stress in the membrane, aligning it according to the layout lines. Use a heat gun to heat the underside of the membrane and the base layer surface until the asphalt appears molten. Then, use a roller to press the membrane edges and gradually roll it down, ensuring full adhesion to the base layer.

4. Joint Treatment: Joints should be at least 100mm wide. The joint area must be sealed independently using the same hot melt method. Overlaps between upper and lower membranes should be 3–5mm wide and evenly straight, with excess melted asphalt squeezed out.

5. Water Test: Conduct a water test according to the construction specifications.

6. Protective Layer Installation: A protective layer should be installed on the outer surface of the waterproofing layer as required by relevant standards or design specifications.

Hot Adhesive Method

The hot adhesive method refers to a composite installation technique using non-curing sealant for waterproof membranes.

1. Base Layer Preparation: Clean the surface thoroughly. The base layer should be solid, flat, and dry.

2. Additional Layer Work: Treat areas such as corners, pipe penetrations, joints, and expansion joints by applying additional reinforcement layers. Cut the membrane into suitable sizes and shapes beforehand.

3. Large-Scale Application: Apply non-curing sealant while simultaneously adhering the waterproof membrane. The thickness of the sealant layer must meet relevant code requirements. Apply the sealant at the same time as pressing the membrane into place.

4. Joint Treatment: The joint area must be sealed independently using the hot melt method. Overlaps between upper and lower membranes should be based on the extruded asphalt line.

5. Water Test: Conduct a water test according to the construction specifications.

6. Protective Layer Installation: A protective layer should be installed on the outer surface of the waterproofing layer as required by relevant standards or design specifications.

Self-Adhesive Method

The self-adhesive method involves using membranes with built-in adhesive layers, requiring no heat or additional adhesive materials—bonding occurs naturally during installation.

1. Base Layer Preparation: The base layer must be solid, flat, dry, clean, free from bumps, oil stains, and dirt. Uneven areas or cracks should be repaired with leveling mortar. Inspect and clean the base layer before work begins; use a vacuum cleaner or high-pressure air blower if necessary.

2. Primer Application: Before installing the membrane, apply a primer evenly across the base layer, covering all areas intended for membrane attachment. Ensure complete coverage without gaps or buildup.

3. Detail Treatment: After priming, treat areas requiring additional waterproofing per relevant codes or design requirements. For hard-to-adhere details, use auxiliary tools like heat guns or heating equipment to assist adhesion. In general, additional layers should fully cover the base layer, with attention to spacing in accordance with code specifications.

4. Large-Scale Application:

Flat Surface: After priming and drying, mark layout lines immediately. First, lay out the pre-cut membrane and allow stress to release. Then, begin installation from one end, gradually unrolling and peeling off the release film. As you roll, peel off the release film and install the membrane from low to high.

Vertical Wall: For wall installations, both the membrane-to-base and membrane-to-membrane joints should be fully bonded. Fix the top edge of the membrane first using metal clamps, then seal the joint tightly with a sealing strip.

5. Protective Layer Installation: After completing the membrane installation and passing inspection, clean the waterproof layer surface thoroughly. Apply protective measures and install the protective layer according to design requirements. A separation layer should be placed between the waterproof layer and the rigid protection layer. Separation materials may include low-grade asphalt felt, geotextiles, or fiberglass cloth.

Flooded Method

The flooded method refers to a technique where flood-type waterproof membranes are applied to non-exposed waterproofing projects, bonding to the base layer using cement slurry or mortar.

1. Base Layer Preparation: The base layer must be solid, flat, dry, clean, free from bumps, oil stains, and dirt.

2. Membrane Application Using Cement Slurry or Mortar: When using cement slurry, add 3%–5% of cement powder by weight. When using cement mortar (mix ratio 1:2), adjust the actual water content based on the base layer’s absorption rate. It is recommended to use ordinary Portland cement (grade 42.5). Mix the slurry thoroughly before spreading it evenly onto the base layer.

3. Large-Scale Application: Place the membrane at the designated position. Pre-roll and release tension before installation. Align the membrane with the reference line, lift the bottom edge, fix one end, then push the membrane forward while using a roller to press and expel air, ensuring tight adhesion on both sides and ahead.

4. Joint Sealing: Use cold self-adhesive method for joints. Adjacent short-side joints should be staggered by at least 1m. For long-side joints, remove the pre-embedded separation tape, align the reference line, and bond directly. Then, seal the joint with a dedicated sealing strip.

Pre-adhesive Method

The pre-adhesive method, also known as the reverse adhesive method, involves placing high-molecular self-adhesive membranes face-down on the substrate, then pouring concrete mix to bond with the membrane’s adhesive layer, forming a permanent integration.

1. Membrane Placement: Cut the membrane accurately. Position the self-adhesive side facing upward toward the structural layer, and the other side facing downward toward the base layer. Install the membrane on the slab, protective wall, underground connection wall, or drainage pipe above ground. (For underground tunnels, use high-molecular membrane with geotextile surface directly fixed to pre-installed anchors.)

2. Joint Sealing: Use the cold self-adhesive method. Remove the pre-embedded separation tape and bond the joints directly. This forms a complete, tightly sealed waterproof system.

3. Reverse Bonding: Peel off the separation film, pour the concrete mix, allowing it to flow and interlock with the membrane’s adhesive layer, creating strong adhesion. The membrane thus bonds permanently to the structural concrete, forming an integrated waterproof system with no interface gaps.

4. If steel mesh is needed, simply remove the separation film and embed it directly—no need to apply additional mortar or concrete for protection.

Why do so many now choose the pre-adhesive reverse bonding method?

Typically, traditional underground wooden construction waterproof membranes are either laid or pre-placed on the base layer, resulting in a physical gap between the waterproof layer and the structural body.

Once damaged, water flows through hidden channels, making leak detection extremely difficult. Repairs are complex and may even lead to total failure of the waterproof system.

In contrast, the pre-adhesive self-adhesive high-molecular waterproof membrane is a superior multi-layer composite material. It is primarily used in various underground storage facilities, tunnels, subways, municipal infrastructure, and other anti-leakage projects. By directly pouring concrete onto the membrane’s bonding surface, the membrane’s special adhesive layer and the flowing concrete form a permanent, inseparable composite body.