I. Core Types and Technical Characteristics of Adhesives for Bonding

1. Epoxy-based Adhesives
   • Core Advantages: Excellent bonding strength (often rated as the highest in independent tests), outstanding chemical resistance, and anti-shrinkage properties. Capable of forming high-strength bonds in narrow gaps (e.g., steel bar grouting).
   • Application Scenarios: Load-bearing projects such as structural repairs (e.g., crack repair of beams and columns), heavy stone dry hanging, and splicing of new and old concrete.
   • Limitations: Sensitive to construction temperature (optimal range: 15-25℃); special formulas are required for underwater bonding.
2. Polyurethane-based Adhesives
   • Core Advantages: Combines high elasticity and waterproofness, capable of adapting to the expansion and contraction deformation of stone and concrete caused by temperature changes (deformation rate up to 10%-20%). Can be applied in dry, wet, or even underwater environments.
   • Application Scenarios: Projects susceptible to environmental influences, such as exterior wall stone cladding, bonding around swimming pools, and floor stone paving.
3. Cementitious Adhesives
   • Core Advantages: Excellent compatibility with concrete substrates, low cost, and environmental friendliness.
   • Application Scenarios: Indoor tiling of small-to-medium-sized stones (≤600×600mm) and non-load-bearing wall decoration.
   • Key Parameters: For powder-type products, the water-to-adhesive ratio must be strictly controlled (1:0.25-0.3) to ensure no agglomeration and effective activation of additives.
4. Acrylic-based Adhesives
   • Core Advantages: Fast curing speed (tack-free time is approximately 40 minutes), flexible operation window, and certain gap-filling capabilities.
   • Application Scenarios: Small-scale DIY projects such as stone repair and partial tile pasting.

II. Standardized Construction Process and Key Control Points

1. Wet Paving Method (Small-to-Medium Indoor Projects)
   • Substrate Treatment: The concrete surface must be polished to a roughness of Ra≥2.5μm. After removing oil stains and floating dust, moisten the surface with clean water (no visible residual water). Cracks should be repaired in advance with epoxy mortar.
   • Adhesive Application:
     • Powdered Adhesive: After stirring, let it stand for 5-10 minutes and then stir again. Use a 6-10mm notched trowel to create continuous ridge patterns.
     • Apply a 2-3mm thin adhesive layer to the back of the stone using the “back-coating method” to ensure full contact.
   • Curing Management: Avoid stepping on or exposing the bonded area to water during the 24-48 hour curing period. Thermal insulation measures must be taken if the temperature is below 5℃.
2. Dry Hanging Method (Large-Scale Outdoor/High-Altitude Projects)
   • Mechanical Assistance: Install a stainless steel/aluminum alloy frame on the concrete substrate and fix it with expansion bolts. The load-bearing capacity of the frame must be 1.5 times the weight of the stone.
   • Bonding Process: Use epoxy adhesive or high-strength polyurethane adhesive. Apply a 3-5mm adhesive layer at the contact points between the angle brackets and the stone, and use mechanical fasteners to form a “double insurance” system.
   • Quality Inspection: Conduct a pull-out test 7 days after curing. The bonding strength must be ≥1.5MPa (qualified if stone failure occurs before adhesive layer failure).
3. General Operation Points
   • Before applying any adhesive, confirm the moisture content of the substrate: ≤6% for concrete and ≤8% for natural stone.
   • For two-component adhesives, strictly mix them according to the specified ratio (error ≤±2%) and stir for no less than 3 minutes.
   • For outdoor construction, avoid rainy days and environments with wind speeds >5m/s. Pre-cool the substrate if the temperature is too high.

III. Five Decision-Making Dimensions for Scientific Adhesive Selection

1. Load Level Matching
   • Light Load (e.g., wall decorative stone): Select acrylic adhesive or cementitious adhesive with a tensile strength of ≥0.5MPa.
   • Heavy Load (e.g., floor stone, structural repair): Must use epoxy adhesive or high-strength polyurethane adhesive with a tensile strength of ≥3.0MPa.
2. Environmental Resistance Requirements

3. Construction Condition Adaptation
   • Emergency Repair Projects: Select fast-curing adhesives.
   • Construction on Wet Substrates: Prioritize products that can bond to wet surfaces.
   • Large-Area Paving: Use barrel-packed cementitious adhesives and match with notched trowels to improve efficiency.
4. Material Compatibility Verification
   • Natural Stone (e.g., marble, granite): Avoid acidic adhesives; epoxy or polyurethane adhesives are recommended.
   • Lightweight Concrete (e.g., AAC blocks): Select flexible adhesives (e.g., Con Bond SBR-modified adhesive) to adapt to substrate shrinkage.
   • Polished Stone: Use high-viscosity adhesives (viscosity ≥10000mPa・s) to prevent adhesive penetration and surface contamination.
5. Compliance and Cost Balance
   • Indoor Projects: Prioritize GREENGUARD-certified products with VOC content ≤50g/L.
   • Budget-Sensitive Projects: Cementitious adhesives cost only 1/3 of epoxy adhesives but require sacrificing some performance.
   • Export Projects: Must comply with standards such as BS 5980:1980 (UK) or ASTM C1248 (US).

IV. Common Problems and Solutions

1. Cracking After Bonding
   • Cause: Insufficient flexibility of the adhesive, failing to adapt to substrate expansion and contraction.
   • Solution: Replace with polyurethane adhesive and reserve 2-3mm expansion joints during construction.
2. Adhesive Penetration and Contamination on Stone Surface
   • Cause: Low viscosity of the adhesive and high porosity of the stone.
   • Solution: Use high-viscosity adhesive and apply masking tape to the stone edges in advance. Wipe contaminated areas with neutral detergent.
3. Bonding Failure in Humid Environments
   • Cause: Use of non-waterproof adhesives.
   • Solution: Switch to waterproof products and remove visible water from the substrate surface before construction.