Complete explanation of polyurethane (PU) sealant for steel structures
Polyurethane sealant for steel structures is a moisture cured elastic sealing adhesive material that is specifically designed to fit the joints of steel sections, H-beams, color steel tiles, steel curtain walls, steel box beams, and steel components. It also has four functions: waterproof sealing, metal anti-corrosion, dynamic deformation tracking, and shock absorption and noise reduction. It is the mainstream filling material for steel structure engineering and complies with the national standard JC/T 482-2022 “Polyurethane Building Sealant”.
Polyurethane sealant support
Glue gun construction
On site gluing of steel structures
1、 Two major categories (selection core)
1) Single component (most commonly used in engineering)
Curing principle: Absorb air moisture and cure from the surface to the inside, apply directly with a glue gun, without the need for mixing ratio
Packaging: 300ml hard support, 600ml soft film bag, no sagging on the facade/top surface
Applicable: on-site steel structure scattered joints, color steel roofs, steel exterior wall panels, door and window steel frames, through wall steel sleeves
Curing speed: 23 ℃/50% humidity, surface drying for 30-60 minutes, surface curing for 24 hours, complete curing in 7 days; Curing significantly slows down in low temperature and dry environments
2) Two component (batch construction of large-area expansion joints and deep joints)
A pre polymer agent+B curing agent, electrically stirred evenly before use, can be poured in large quantities
It must be used up within 30 minutes after mixing, or gel shall be scrapped in advance
Commonly used for expansion joints in steel box girders, settlement joints in steel structures, extra long through joints, and steel structure joints in reservoirs
2、 Core performance (advantages of steel structure adaptation)
1) Elasticity&Displacement Capability (Steel Structure Rigid Requirements)
Tensile elongation at break ≥ 400%, elastic recovery rate ≥ 80%, divided into low modulus grades of 20LM and 25LM
It can follow the thermal expansion and contraction of steel, wind vibration, and load deformation, and the joints can repeatedly expand and contract without cracking or peeling off; Silicone adhesive has high rigidity and dynamic steel joints are prone to detachment
Shore A hardness of 40-50, flexible but not brittle, excellent earthquake resistance and fatigue resistance
2) Metal bonding anti-corrosion ability
Strong adhesion to carbon steel, galvanized steel, color steel plate, aluminum alloy, and rust proof primer paint surfaces, with no need for primer in most working conditions; Rusted steel plates are reliably bonded after grinding and rust removal
Seal and isolate rainwater, water vapor, and salt spray to prevent pitting and rusting of steel plate joints, while blocking the infiltration of corrosive media into the interior of steel components
3) Temperature and weather resistance parameters
Long term use temperature: -40 ℃~+80 ℃, stable and non cracking due to outdoor day night temperature difference and extreme temperatures in winter and summer
Resistant to UV, ozone, freeze-thaw cycles, with an outdoor steel structure service life of 15-20 years
Resistant to mild engine oil and rainwater erosion, it can be used for a long time in factories, outdoor overpasses, and bridge steel structures
4) Can be painted after construction (unique advantage)
The cured surface can be directly coated with steel structure anti rust paint and topcoat, without any shrinkage or undercutting of the paint film, and the exterior is aesthetically pleasing and integrated; Ordinary neutral silicone adhesive cannot be painted and can only expose the adhesive seam
3、 Precision application scenarios for steel structures
Roof system: color steel tile lap joints, gutter steel edges, roof panel purlin splicing, daylighting panels and steel frame sealing waterproofing
Building steel structure: H-shaped steel column beam joint, steel curtain wall vertical and horizontal keel gap, external wall steel hanging plate gap, steel structure enclosure wall panel filling gap
Bridges/Heavy Industries: Expansion joints of steel box girders, splicing of steel box girder wing plates, sealing around steel structure supports, shear joints of crane girder web plates
Supporting nodes: steel door and window frame wall closure, steel structure through wall sleeve, equipment steel base gap, steel ladder maintenance platform gap
Composite interface: Steel+concrete beam column nodes, sealing of steel components and stone/glass composite joints
4、 Standard construction process flow (steel joints must be made to avoid delamination and water leakage)
- Basic surface pretreatment (key to success or failure)
Steel plate joints are polished with a wire brush and angle grinder to remove rust, floating paint, oil stains, and dust; Galvanized sheet wiping release agent
Wipe clean with solvent (acetone/anhydrous ethanol), and the base surface must be dry. Moisture will cause adhesion failure
The polyethylene foam backing rod shall be embedded with the seam width ＞ 10mm, and the diameter shall be 15% larger than the seam width to prevent the sealant from losing elasticity when sticking on three sides; The width to thickness ratio of the adhesive should be controlled within 2:1 - Glue application steps
The rubber nozzle is slanted at a 45 ° angle, with a diameter slightly smaller than the width of the seam. The rubber nozzle is inserted into the bottom of the seam and pushed at a constant speed, filling the interior without bubbles. It is strictly prohibited to scrape only one layer on the surface
Within 30 minutes, use a scraper to compact and trim the edges, ensuring smooth and full adhesive joints
Maintenance: Do not expose to rain or touch within 24 hours; Extended curing in low temperature (<5 ℃) and high humidity environments for 48 hours; after 7 days of complete curing, topcoat can be applied and a closed water test can be conducted
5、 Comparison of advantages and disadvantages
✅ advantage
Highly elastic and adaptable to dynamic deformation of steel components, with no cracks in dynamic joints, far exceeding silicone weather resistant adhesive
Strong adhesion of steel surface, with dual functions of sealing and anti-corrosion
After curing, it can be painted, and the exterior surface has no obvious color difference in adhesive joints
Non corrosive type, does not corrode galvanized layer, steel structure primer
Single component ready to use, high on-site construction efficiency for high-altitude steel structures
❌ shortcoming
Long term immersion of pure polyurethane in strong acidic and alkaline wastewater has weak performance, and the steel structure of the chemical tank needs to be customized with chemical resistant modified versions
Single component deep thick adhesive has slow internal curing, and it is recommended to apply adhesive layer by layer for ultra deep seams
Extremely low humidity (RH<30%), winter construction curing is extremely slow, can be accelerated with a base coat