How to seal the “joints” of the building’s exterior wall? If the expansion joint glue is not selected correctly, cracking and leakage are inevitable!

The purpose of the existence of building expansion joints, curtain wall panel joints, large prefabricated component joints… is to allow the structure to produce significant relative displacement due to temperature changes, wind loads, earthquakes and other factors. To seal these “movable joints”, special sealants that can withstand large displacements, high elasticity, and super weather resistance are required.

Core skills: high displacement capacity, special design, precise construction, backing control

Core requirements: extremely high displacement capacity

Movement Capability: This is the primary indicator for selecting such sealants. It indicates the maximum percentage (±%) of the change in joint width (stretching and compression) that the sealant can withstand without damage (cracking or debonding). Common grades are ±25%, ±35%, ±50% or even higher (such as ±100%).

How to choose: A sealant with a higher displacement capacity must be selected based on the expected displacement of the engineering design (usually requiring the sealant capacity to be ≥ 1.5 times the design displacement). High-rise buildings, areas with large temperature differences, long seams, curtain walls, etc. usually require ±35% or ±50% levels.

Materials: High-performance neutral silicone structural sealants or silicone weathering sealants are the absolute mainstream. They have the best elastic recovery rate (ability to rebound after deformation) and ultra-long weathering life (resistance to UV, ozone, extreme temperatures).

Special adhesives and professional design:

Structural adhesives vs. weathering adhesives:

Structural sealants: Extremely high strength (tensile bonding strength> 0.6MPa or even above 1.0MPa), used for structural bonding and fixing of curtain wall panels and frames (bearing self-weight, wind pressure, and seismic forces). Strict calculation and certification are required.

Weathering sealants: Mainly play the role of waterproof sealing, adapting to displacement, and isolating the environment. Used for sealing the surface of curtain wall panel seams and expansion joints. Displacement capacity is its core indicator. Strength requirements are usually lower than structural adhesives (but bonding must be reliable).

Follow the specifications: You must strictly follow the relevant national/industry standards (such as JGJ 102, GB 16776) and design requirements, and choose certified products (such as those that meet national standards and American standards ASTM C920).

Construction key (highly professional, usually operated by a professional team):

Joint design and backing: Joint width and depth design are crucial. Closed-cell polyethylene (PE) foam rods must be used as backing materials:

Control the thickness of the sealant (the ideal thickness is half the seam width, usually between 6-12mm, and the maximum does not exceed 20mm).

Ensure two-sided bonding (the glue only bonds the sides of the gap, not the bottom), which is the key to stress release and displacement adaptation! Three-sided bonding is the root cause of failure (the glue will be torn).

Prevent sealant from sagging (reverse seams, top seams).

Substrate treatment: Extremely important! Strictly treat the bonding surface according to the requirements (sandblasting, solvent cleaning, primer, etc.) to ensure cleanliness, dryness and compatibility.

Primer: For porous substrates (concrete, stone) or difficult-to-bond substrates (certain coated metals, PTFE membranes), a special primer specified by the manufacturer must be used to significantly improve bonding reliability and durability.

Full filling and standardized trimming: Ensure that the colloid fills the joints completely, continuously, and without bubbles. Use special tools to trim into the designed shape (usually concave).

Curing conditions: Pay attention to temperature and humidity requirements to ensure sufficient curing.

💡 Key points: Large displacement joints are the top challenge for sealant application! Be sure to use special silicone glue with a high displacement grade (starting from ±35%), strictly use PE backing rods to ensure bonding on both sides, and substrate treatment and primer are carried out according to specifications. Non-professionals should not try it easily!