Mastic is a moisture-proof and vapor barrier material made from bitumen as the base material, added with mineral fillers and appropriate amount of flame retardants, namely waterproof flame retardant mastic. It possesses characteristics such as air tightness, waterproofing, frost resistance, corrosion resistance, resistance to aging and cracking, and flame retardancy after cold construction at room temperature.

Moisture-proof mastic plays a crucial role in pipeline insulation projects, especially in the field of cryogenic pipeline insulation for LNG and other applications, where it demonstrates unique advantages. This article systematically elaborates on the key application points of moisture-proof mastic in pipeline insulation projects from aspects such as material properties, technical parameters, construction technology, and comparative analysis with other moisture-proof materials, providing professional reference for material selection in engineering projects.

I. Material Properties Analysis of Mastic

1. Basic Composition and Structure
Mastic is a composite material, mainly composed of asphalt or polymer resin as the base material, with the addition of mineral fillers, flame retardants, plasticizers, thickeners, and other auxiliary components. Depending on the application requirements, mastic can be divided into two types: thermal insulation and cold insulation. Cold insulation mastic is usually a black paste with higher density and a lower operating temperature range. The core characteristics of cold insulation mastic are airtightness, waterproofness, and antifreeze properties, while also possessing advantages such as corrosion resistance, resistance to aging and cracking, and cold application at room temperature. Its internal structure contains asphalt base material, flame retardants, plasticizers, and mineral fillers, forming a gel-like substance with high adhesion. 2. Physical and Chemical Properties

Physical Properties:

- Density: 1.5-1.7 g/cm³ (cold insulation type), higher than thermal insulation type (1.1-1.3 g/cm³)

- Application Thickness: 3-6 mm, specific thickness determined according to project requirements

- Drying Time: 48-60 hours, finger-drying time approximately 1 hour

- Water Absorption: ≤1.0% (cold insulation type), significantly lower than thermal insulation type (≤2.0%)

- Environmental Adaptability: Adaptable to temperature changes from -40℃ to +60℃, no cracking or detachment after 2 hours of hanging

Chemical Properties:

- Flame Retardancy: B2 grade, non-igniting during application, self-extinguishing within 1 second after removal from heat source, oxygen index >30% (OI)

- Temperature Range: Operating temperature range is -40℃ to 90℃, but special formulations can extend to -170℃ to 120℃. - Adhesion Strength: 1.5-2.5 kg/cm² at 20℃, exhibiting good adhesion to metals, foam glass, polyurethane, and other materials.

- Corrosion Resistance: High-performance corrosion inhibitors are added, effectively preventing the chemical and physical effects caused by external media ingress.

II. Special Requirements for Moisture-Proof Layers in Pipeline Insulation Projects

1. Performance Requirements in Low-Temperature Environments
Pipeline insulation projects typically involve ultra-low temperature environments (e.g., approximately -162℃ for LNG pipelines), imposing special requirements on moisture-proof layer materials:
* Low-Temperature Stability: The material must maintain good mechanical properties in ultra-low temperature environments, particularly resistance to brittleness, impact, and shrinkage. Although conventional mastic products only withstand temperatures up to -40℃, specially formulated products can meet ultra-low temperature requirements down to -162℃, which is particularly important in ultra-low temperature pipeline insulation projects such as LNG. 1. Air tightness and waterproofness: The moisture barrier must possess excellent air tightness and waterproofness to prevent external moisture from seeping into the insulation layer, causing the insulation material to absorb moisture and freeze, thus reducing insulation efficiency. The high adhesion and low water absorption of mastic make it an ideal moisture barrier material.

2. Long-term stability: The material needs to maintain structural and performance stability in low-temperature environments for extended periods, avoiding cracking and deformation caused by temperature changes. The addition of corrosion inhibitors and plasticizers to mastic helps improve its long-term stability.

3. Structural and construction requirements: According to GB50264-2013 <Code for Design of Thermal Insulation Engineering for Industrial Equipment and Pipelines>, the pipeline insulation structure generally consists of an insulation layer, a moisture barrier, and a protective layer. Structural Integrity: The moisture barrier should maintain its structural integrity and airtightness, even under environmental changes and vibrations. The layered application process of mastic (applying the first layer, then reinforcing material, followed by the second layer) helps improve structural integrity.
Compatibility with Insulation Layers: The moisture barrier needs good adhesion to insulation materials (such as foam glass, polyurethane, PIR, etc.) to ensure the integrity of the overall structure. Mastic bonds well to a variety of materials, with an adhesion strength of 1.5-2.5 kg/cm², meeting this requirement.
Connection with Protective Layers: If binding materials are used on the outside of the moisture barrier, the moisture barrier must not be damaged. The dense layer formed after the mastic dries effectively prevents damage to the moisture barrier from binding materials.

III. Application and Construction Techniques of Mastic in Pipeline Insulation

1. Application Methods
Mastic is mainly used as a moisture barrier in pipeline insulation projects, usually in conjunction with insulation materials such as foam glass, polyurethane, and rigid microporous calcium silicate. Specific applications are as follows: Rigid insulation structure: In cryogenic insulation projects such as LNG pipelines, mastic is often used as the primary moisture barrier, forming a complete moisture-proof system together with the inner secondary moisture barrier (such as aluminum foil). A typical structure, from the inside out, consists of: a transition layer (1-2cm inorganic fiber material), an insulation layer, a moisture barrier (mask), and an outer protective layer (such as aluminized steel plate or color steel plate). Flexible insulation structure: For flexible insulation materials (such as FEF/LT+LTD combinations), mastic is typically used for sealing special areas (such as valves, flanges, etc.) to prevent moisture from seeping in from these discontinuous areas.

2. Key points of construction process: The construction process of mastic directly affects the moisture-proof effect, mainly including the following steps: Substrate treatment:

- Remove dust, oil, and loose particles from the surface of the insulation layer.

- Ensure the surface of the insulation layer is flat, without cracks or sharp protrusions.

- The moisture content of the insulation layer surface must be ≤8% to avoid moisture affecting the bonding effect.

- For special areas (such as valves and flanges), pretreatment is required to ensure sealing.
Material Configuration:

- Prepare mastic according to design specifications, controlling the ratio of asphalt base material to flame retardant.

- For applications requiring hot application, heat to 180-190℃; the operating temperature should not be lower than 160℃.

- Ensure the mastic's heat resistance is ≥95℃ and its flexibility meets standards.
Layered Coating Process:

- First Layer: Apply a 1-3mm thick layer of mastic evenly, covering the surface of the insulation layer and embedding fiberglass cloth or plastic window screen to enhance crack resistance.

- Second Layer: After the first layer is surface dry (approximately 1 hour), apply a 2-3mm thick layer of mastic, controlling the total thickness to 5-6mm.

- Coating Method: Use a long-handled bristle brush or roller to apply in the same direction, avoiding repeated back-and-forth brushing which can cause material cooling and delamination.

- Special Area Treatment: For complex areas (such as pipe roots, valves, and flanges), a scraper can be used to assist in scraping to ensure no areas are missed.
Sealing Treatment: Fiberglass cloth or plastic window screen should be laid before the mastic dries to ensure the reinforcing material fully integrates with the mastic.

- Apply evenly, ensuring a smooth surface free of bubbles and cracks.

- For disconnections such as valves and flanges, apply mastic in a 10-20° conical shape to enhance the sealing effect.

Precautions:

- Ensure good ventilation at the construction site to facilitate mastic drying.

- Seal and store any remaining mastic after application to prevent hardening.

- The application rate of mastic is approximately 6-8 kg/m² (including losses).

- After drying, mastic has flame-retardant and waterproof properties, but safety precautions must be taken during application to avoid contact with fire sources.

IV. Technical Parameters and Performance Evaluation of Mastic

1. Key Technical Parameters
As a pipe insulation and moisture-proof layer material, mastic must meet specific technical parameters:

| Parameter Item | Cold Insulation Mastic | Thermal Insulation Mastic | Industry Standard Requirements |

|---------|------------|------------|------------|

| Appearance | Black Paste | Blue (white) paste | - |

| Density | 1.5-1.7g/cm³ | 1.1-1.3g/cm³ | - |

| Operating Temperature | -40℃ to 90℃ (special formulas can reach -170℃) | -25℃ to 120℃ | - |

| Water Absorption | ≤1.0% | ≤2.0% | - |

| Application Thickness | 3-6mm | 3mm | - |

| Drying Time | 48-60 hours (approximately 1 hour for finger drying) | 48 hours | - |

| Application Amount | 12.5kg/m² | 3.5kg/m² | - |

| Flame Retardancy | B2 grade (Oxygen Index >30%, Self-extinguishing Time ≤1 second) | - | - |

| Heat Resistance | 95℃ tilted for 4 hours, 120℃ tilted for 1 hour, no dripping or bubbling | - | - |

| Freeze Resistance | No cracking or detachment after hanging for 2 hours at -40℃ to +60℃ | - | - |

| Adhesion | 1.5-2.5 kg/cm² at 20℃ | - | - |

| Elongation | 3% | - | - |

| Packaging Specifications | 25 kg/drum | 20 kg/drum | - |

| Storage Conditions | -5℃—45℃, protected from light | -5℃—35℃, protected from light | - |

| Shelf Life | 1-2 years | 1 year | - |

2. Performance Evaluation: For the specific needs of pipeline insulation projects, the performance indicators of mastic are evaluated as follows: Cryogenic Adaptability: Although conventional mastic products only withstand temperatures up to -40℃, specially formulated products (such as flame-retardant mastic for PIR insulation) can be extended to -170℃, meeting the cryogenic pipeline insulation requirements for LNG and other applications. It should be noted that this parameter needs to be certified by a third party or verified in actual engineering projects to ensure long-term stability in an LNG pipeline environment at -162℃. Airtightness and Water Resistance: The airtightness and water resistance of mastic are its core advantages. Its water absorption rate is ≤1%, far lower than that of general waterproof materials. This allows it to effectively prevent external moisture from penetrating into the insulation layer, avoiding moisture absorption and freezing of the insulation material, thereby maintaining pipeline insulation. Cold Efficiency.
Frost Resistance and Heat Resistance: The mastic exhibits frost resistance of -40℃ to +60℃ with no cracking or detachment after 2 hours of hanging. Its heat resistance is excellent, showing no flow or bubbling after 4 hours of inclined placement at 95℃ and 1 hour of inclined placement at 120℃, meeting the temperature fluctuation requirements of conventional pipeline insulation projects. For ultra-low temperature pipelines, special formulations must be selected and actual testing verified.
Convenience of Construction: Mastic can be applied cold at room temperature without a curing period, shortening the construction time. Its adhesion to various base materials (such as foam glass, polyurethane, rigid microporous calcium silicate, metals, etc.) reaches 1.5-2.5 kg/cm², ensuring a tight bond between the moisture-proof layer and the insulation layer. However, its drying time is relatively long (48-60 hours), which may affect the construction progress. Economic Efficiency: The application rate of mastic is approximately 12.5 kg/m², which is relatively high compared to other moisture-proof materials (such as aluminum foil/PAP composites). However, its excellent airtightness and waterproofness can reduce the thickness of the insulation layer, thus saving overall material costs. Furthermore, the corrosion resistance of mastic can extend the service life of pipelines and reduce maintenance costs.

V. Comparative Analysis of Mastic and Other Moisture-Proof Materials

1. Main Types of Moisture-Proof Materials
Commonly used moisture-proof materials in pipeline insulation projects include:

- Mastic: A composite material made from asphalt or polymer resin as a base, with added mineral fillers, flame retardants, etc.

- Aluminum Foil/PAP Composite Material: Composed of aluminum foil and polyethylene (PAP), with a thickness generally of 0.15-0.20 mm.

- Polyurethane Waterproof Membrane: A waterproof membrane based on polyurethane, possessing excellent elasticity and self-healing properties.

- Fiberglass Reinforced Plastic (FRP) Outer Sheath: An outer sheath material based on glass fiber reinforced plastic.

2. Comprehensive Performance Comparison

The following is a comprehensive performance comparison of mastic with other moisture-proof materials:

| Performance Indicators | Mastic | Aluminum Foil/PAP | Polyurethane Waterproof Membrane | Fiberglass Outer Sheath |

|---------|-------|---------|--------------|------------|

| Air Tightness | Excellent (water absorption ≤1%) | Good (requires multi-layer application) | Good (excellent elasticity) | Average (requires auxiliary sealing) |

| Waterproofing | Excellent (cold application at room temperature) | Good (hot-melt overlap) | Excellent (impermeable) | Good (requires auxiliary waterproofing) |

| Low Temperature Resistance | Standard -40℃ (special formula -170℃) | Standard -20℃ (requires composite material reinforcement) | Standard -20℃ (special modification up to -180℃) | Good (but high thermal conductivity) |

| Ease of Construction | Moderate (requires layered application) | Excellent (hot-melt overlap) | Good (Self-adhesive) | Average (Requires professional installation) |

| Mechanical Strength | Good (Strong adhesion) | Average (Low elongation) | Excellent (Elastic recovery) | Excellent (High structural strength) |

| Lifespan | 25 years (Good corrosion resistance) | 10-15 years (Requires metal protective layer) | 10-15 years (Prone to aging) | 30 years (Strong corrosion resistance) |

| Cost | Medium (Large construction workload) | Low (Low material usage) | Medium (High modification cost) | High (High material cost) |

| Applicable Scenarios | Complex structural parts of cryogenic pipelines (such as LNG) | Scenarios requiring rapid construction in conventional cryogenic pipelines | Scenarios requiring self-healing function in medium and low temperature pipelines | Highly corrosive environments in non-cryo-cryo areas |

3. Selection Recommendations
For different application scenarios, the following are the selection recommendations for mastic and other moisture-proof materials: Cryogenic pipelines (such as LNG):

- - **Preferred choice:** Mastic: Its special low-temperature formula meets ultra-low temperature requirements down to -162℃, and its excellent airtightness and waterproofing effectively prevent external moisture penetration.

- **Secondary choice:** Polyurethane waterproof membrane: If the pipeline temperature is in the range of -180℃ to -40℃ and rapid construction is required, consider specially modified polyurethane waterproof membrane.

- **Not recommended:** Aluminum foil/PAP: Conventional aluminum foil only withstands temperatures down to -20℃, and even PAP composite materials struggle to meet ultra-low temperature requirements.

**Conventional low-temperature pipelines:**

- Mastic: Suitable for pipeline insulation from -40℃ to 90℃, especially suitable for sealing complex structural components (such as valves and flanges).

- Aluminum foil/PAP: Lightweight and quick to install, suitable for moisture-proof layers on standard pipelines, but requires multiple layers to enhance sealing.

- Polyurethane waterproof membrane: Excellent elasticity and self-healing properties, suitable for medium- and low-temperature pipelines requiring frequent maintenance.

**Coastal high-corrosion environments:**

- Mastic: Contains high-performance corrosion inhibitors, exhibiting excellent salt spray corrosion resistance, suitable for highly corrosive environments such as coastal LNG receiving stations.

- Fiberglass outer sheath: Excellent corrosion resistance, but high thermal conductivity, unsuitable for the outer sheath of cryogenic pipelines.

VI. Connection Process between Mastic and Color Steel Plate Metal Layer

1. Installation Sequence and Connection Method

In pipeline insulation projects, the connection process between the mastic moisture-proof layer and the color steel plate metal layer is as follows:

Typical Installation Sequence:

1. Begin insulation construction after the pipeline water pressure test is passed.

2. Clean the pipeline surface, removing oil and rust.

3. Lay the transition layer, insulation layer, and mastic moisture-proof layer in sequence.

4. Finally, install the outer protective layer of the color steel plate metal layer and perform sealing treatment.

5. Check the integrity and sealing of the outer sheath.

Connection Method:

- After the mastic dries (approximately 48-60 hour

Jiangsu Huasang Thermal Insulation Technology Co., Ltd., established in 2012, is located at No. 1 and No. 18 Victory Road, Chunjiang Town, Xinbei District, Changzhou City, Jiangsu Province (two factory areas). The registered capital is 30 million yuan, and by the end of 2021, the company's annual sales revenue had exceeded 60 million yuan. Jiangsu Huasang Thermal Insulation Technology Co., Ltd. has always been committed to providing advanced cryogenic system professional solutions for a wide range of industrial customers. Main products include thermal insulation materials, cryogenic pipe supports, and cryogenic construction engineering. Jiangsu Huasang Thermal Insulation Engineering Co., Ltd., a wholly-owned subsidiary of Jiangsu Huasang Thermal Insulation Technology Co., Ltd., specializes in deep cryogenic construction services. It holds national second-level anti-corrosion and thermal insulation construction qualifications, system certification certificates, and safety production permits.