Sealing

Sealing — RTV Silicone Sealants and Gasket Materials

Sealing — preventing the passage of fluids, gases, or contaminants across an interface — is one of the largest single markets for silicone materials globally. The market spans construction sealants (curtain wall, expansion joints, plumbing), automotive seals (engine, transmission, body), industrial seals (process equipment, instrumentation), and aerospace seals (fuel system, cabin, engine).

Three silicone product families serve sealing:

RTV (Room Temperature Vulcanizing) sealants: paste-form silicones that cure on application to form an elastomeric seal in-situ. The dominant chemistry for construction and field-applied industrial sealing.
Pre-formed silicone gaskets: molded or extruded silicone rubber profiles, used as static seals between two assembled components. Dominant for engine gaskets, automotive body seals, and equipment housings.
Liquid silicone (LSR) molded seals: precision injection-molded silicone elastomer for high-volume sealing applications, especially baby products, medical devices, and consumer electronics.

Construction Sealing

Construction sealants are the largest single application of silicone sealants by volume:

Structural glazing (SSG): two-component structural silicone bonds glass directly to aluminum mullions in curtain-wall construction. Movement capability ±25%, 30+ year warranty. Approved per ETAG 002 / ASTM C1184.

Weatherproofing joints (non-structural): single-component neutral-cure silicone sealants per GB 16776 / ASTM C920 fill movement joints around windows, expansion joints in walls, and panel-to-panel seams. Movement capability ±50% in premium grades.

Plumbing seals: single-component acetoxy-cure silicone sealants (gen-1 chemistry, vinegar smell during cure) for kitchen and bath fixture sealing. Lower cost than neutral cure but cannot be used on stone or alkaline substrates.

Glass-to-glass and glass-to-metal: structural and weather-seal silicone for skylight, atrium, and glass façade construction. Often pre-applied at fabrication.

Automotive Sealing

Automotive sealing combines extreme service requirements (engine compartment temperatures up to 200 °C, sustained vibration, exposure to fuels, oils, and salt) with high-volume production. Major silicone applications:

Engine gaskets: silicone rubber valve cover gaskets, intake manifold gaskets, oil pan gaskets. Standard HTV silicone or LSR.

Transmission seals: silicone-rubber seals around shift rods, axle interfaces. Often fluorosilicone (FVMQ) for fuel-tolerant service.

Body seals: door perimeter seals, window glazing seals, hood seals. Silicone for premium applications; EPDM more common in mass-market vehicles.

Spark plug and ignition wire boots: HTV silicone, often phenyl-modified for engine compartment temperature service.

EV battery pack sealing: emerging large-volume application. Silicone gaskets and sealants must combine sealing, thermal management, and fire-retardant performance for the battery enclosure.

Industrial and Process Equipment Sealing

Industrial sealing applications often require specific certifications:

Food contact (FDA 21 CFR 177.2600 for silicone rubber, GB 4806.11 for China): for food-processing equipment, dairy plant fittings, beverage manufacturing
Pharmaceutical (USP Class VI): for pharma manufacturing equipment, sterile processing
High-temperature process (continuous to 230 °C): for chemical reactors, autoclaves, drying ovens
Chemical resistance (specific solvents): silicone elastomer for water-based and weak chemical service; fluorosilicone for hydrocarbon service; perfluoroelastomer (FFKM) for aggressive chemicals where silicone is not suitable

RTV Sealant Cure Chemistries

Single-component RTV sealants come in four cure chemistries:

Acetoxy (acid cure, vinegar smell): cheapest, fast cure, but corrosive to copper and brass. Plumbing and DIY.
Oxime (cure with neutral byproducts): standard for most general-purpose construction sealants.
Alkoxy (alcohol byproduct): neutral cure, suitable for stone and alkaline substrates. Premium construction grades.
Amine (cure with amine byproducts): rare; specialty applications.

Two-component RTV-2 systems include:

Tin-condensation: traditional, slower cure, tin catalyst
Platinum-addition: faster cure, no byproducts, used for medical and food-contact

Test Methods

Sealing performance measured by:

Cure depth and tack-free time: how fast the sealant skins over and reaches structural cure
Movement capability (ASTM C719): cyclic movement testing at +/-12.5% to +/-50% range
Adhesion to substrates (ASTM C794, C1521): peel and bond strength on various substrates after weathering
Compression set (ASTM D395): for static gaskets, measures permanent deformation
Long-term aging: ASTM C920 includes 5000+ hour QUV and immersion testing

Sourcing Notes

For construction sealants, the major brands include Dow, Sika, Wacker, Henkel, GE Momentive (now Momentive). Chinese sealant producers (BJZB, Zhongtian, Hangao) supply local construction markets. International export typically requires GB 16776 + ASTM C920 dual certification.

For automotive and industrial sealing, OEM specifications drive supplier selection. Large-volume Chinese supply has grown significantly in non-OEM aftermarket but Tier-1 OEM supply remains concentrated among Western and Japanese sealant brands.