Sealant

Not to be confused withSealand.

Self-levelingsiliconefirestopsystemused aroundpipethrough-penetration in atwo-hour fire-resistance ratedconcretefloor assembly.

Sealantis a substance used to block the passage offluidsthrough openings in materials,a type ofmechanical seal.In building constructionsealantis sometimes synonymous withcaulk(especially if acrylic latex or polyurethane based)and also serve the purposes of blocking dust, sound and heat transmission. Sealants may be weak or strong, flexible or rigid, permanent or temporary. Sealants are notadhesivesbut some have adhesive qualities and are calledadhesive-sealantsorstructural sealants.

History

Sealants were first used in prehistory in the broadest sense as mud, grass and reeds to seal dwellings from the weathersuch as the daub inwattle and daubandthatching.Natural sealants and adhesive-sealants included plantresinssuch as pine pitch andbirch pitch,bitumen,wax,tar,natural gum,clay (mud) mortar,lime mortar,lead,blood and egg. In the 17th century glazingputtywas first used to seal window glass made with linseed oil and chalk, later otherdrying oilswere also used to make oil-based putties.In the 1920s,polymerssuch asacrylic polymers,butylpolymers and silicone polymers were first developed and used in sealants. By the 1960s, synthetic-polymer-based sealants were widely available.

Function

Sealants, despite not having great strength, convey a number of properties. They seal top structures to the substrate, and are particularly effective inwaterproofingprocesses by keeping moisture out (or in) the components in which they are used. They can provide thermal and acoustical insulation, and may serve as fire barriers.They may have electrical properties, as well. Sealants can also be used for simple smoothing or filling. They are often called upon to perform several of these functions at once.

A caulking sealant has three basic functions: It fills a gap between two or more substrates; it forms a barrier due to the physical properties of the sealant itself and by adhesion to the substrate; and it maintains sealing properties for the expected lifetime, service conditions, and environments. The sealant performs these functions by way of correct formulation to achieve specific application and performance properties. Other than adhesives, however, there are few functional alternatives to the sealing process.

Solderingorweldingcan perhaps be used as alternatives in certain instances, depending on the substrates and the relative movement that the substrates will see in service. However, the simplicity and reliability offered by organic elastomers usually make them the clear choice for performing these functions.

Types

A sealant may be viscous material that has little or no flow characteristics and which stay where they are applied; or they can be thin and runny so as to allow it to penetrate the substrate by means ofcapillary action.

Anaerobic acrylic sealants (generally referred to as impregnants) are the most desirable, as they are required to cure in the absence of air,unlike surface sealants that require air as part of the cure mechanism that changes state to become solid, once applied, and is used to prevent the penetration of air, gas, noise, dust, fire, smoke, or liquid from one location through a barrier into another.

Typically, sealants are used to close small openings that are difficult to shut with other materials, such asconcrete,drywall,etc. Desirable properties of sealants include insolubility,corrosionresistance, andadhesion.Uses of sealants vary widely and sealants are used in many industries, for example,construction,automotiveandaerospaceindustries.

Sealants can be categorized in accordance with varying criteria, e. g. in accordance with the reactivity of the product in the ready-to-use condition or on the basis of its mechanical behavior after installation.

Often the intended use or the chemical basis is used to classify sealants, too. A typical classification system for most commonly used sealants is shown below.

Classification of sealants by reactivity and chemistry

Types of sealants fall between the higher-strength, adhesive-derived sealers andcoatingsat one end, and extremely low-strength putties, waxes, and caulks at the other. Putties and caulks serve only one function – i.e., to take up space and fill voids. Sealants may be based onsilicone.

Other common types of sealants:

• Acrylic resins
• Acrylic latex
• Acoustic sealants
• Adhesive sealants
• Butyl rubber
• Dental sealants
• Elastic sealants
• Electronic sealants
• Epoxythermosets
• Extruded sealants
• Fibrin glue
• Firestopbarrier sealants
• Floor sealant
• Foam
• Grout
• Hotwax
• Impregnating sealants
• Latex sealants
• Metal sealants
• Patio sealants
• Paint sealants
• Plastic sealants
• Polysulfidesealants
• Polyurethanesealants
• Rubber sealants
• Sealcoat
• Seam sealants
• Silicone sealant
• Spackling paste
• Stone sealer
• Surgical sealant
• Tile sealant
• Urethane sealants
• Valve seal
• Varnish
• WKT

Common areas of use

• Automotive industry
• Architectural
• Asphalt
• Pipe threads
• Aerospace industry
• Aircraft
• Aquariums
• Casting
• Cement/Concrete
• Engines
• Gaskets
• Glass
• HVAC systems
• Hydraulic systems
• Marine industry
• Military grade
• Radiators
• Reservoirs
• Roofs
• Tires
• Wood

Aerospace sealants

• Firewall Sealants – a two-component, firewall sealant intended for use as a coating, sealant or filleting material in the construction, repair and maintenance of aircraft and is especially useful where fire resistance, exposure to phosphate ester fluids, and/or exposure to extreme temperatures, −65 °F (−54 °C) to 400 °F (204 °C) are major considerations.
• Fuel Tank Sealants – High-temperature fuel resistant sealant intended for use on integral fuel tanks with excellent resistance to other fluids such as water, alcohols, synthetic oils and petroleum-based hydraulic fluids
• Access Door Sealants – Access door sealant intended for use on integral fuel tanks and pressurized cabins with low adhesion characteristics and excellent resistance to other fluids such as water, alcohols, synthetic oils and petroleum based hydraulic fluids.
• Windshield Sealant – demonstrated to be a useful sealant in a variety of applications where quick setting is desired, for example, windshield sealants, repair caulks, adhesives, etc.

Comparison with adhesives

The main difference betweenadhesivesand sealants is that sealants typically have lower strength and higher elongation than adhesives do. When sealants are used between substrates having different thermal coefficients of expansion or differing elongation under stress, they need to have adequate flexibility and elongation. Sealants generally contain inert filler material and are usually formulated with anelastomerto give the required flexibility and elongation. They usually have a paste consistency to allow filling of gaps between substrates. Low shrinkage after application is often required. Sealants also typically require a sufficient compression set, especially when the sealant is a foamgasket.Many adhesive technologies can be formulated into sealants.