Common Skylight Sealants and Gasket Materials
Silicone, Butyl Rubber, Urethane, Thermoplastics, EPDM, and Neoprene will be discussed as these materials are used in various
installations. Each material will be described separately.
Silicone Sealants
- Only structural silicone sealants have the long-term adhesion, compatibility, and strength required for structural glazing and protective glazing
applications.
- Silicones have greater UV stability, temperature, and weather resistance than organic materials.
- Silicones are inherently waterproof.
- Silicones remain flexible over a wide temperature range and are easy to apply in cold weather.
- Silicones last longer and need to be replaced less often than many organic materials, which reduces lifetime costs and contributes to sustainability.
Silicones generally outperform and outlast organic weatherproofing materials. They also enable innovative applications that would otherwise
be impossible. Silicone architectural coatings typically last twice as long as acrylic coatings and silicone building sealants typically last
three times as long as urethane sealants. Silicones for construction come in many forms:
- Preformed rubber shapes and extrusions
- Waterproofing fluids and emulsions
- Elastomeric adhesives, sealants, and architectural coatings
- Free-flowing resins
- Flexible rubbers
- Greases
- Fluids thinner than water or thick as paste
Silicones are both water repellent and “breathable.” They can keep rain from entering a building while letting water vapor trapped inside the
building escape.
Butyl Rubber Sealants
Butyl rubber sealant is used for rubber roof repair and for maintenance of roof membranes (especially around the edges). It is important to
have the roof membrane fixed, as a lot of fixtures (i.e., air conditioner vents, plumbing and other pipes, etc.) can considerably loosen it.
Rubber roofing typically refers to a specific type of roofing materials that are made of ethylene propylene diene monomers ( EPDM). It is crucial
to the integrity of such roofs to avoid using harsh abrasive materials and petroleum-based solvents for their maintenance. Polyester fabric
laminated to butyl rubber binder provides a single-sided waterproof tape that can be used on metal, PVC, and cement joints. It is ideal for
repairing and waterproofing metal roofs. Butyl rubber is one of the most robust elastomers. It is a harder and less porous material than other
elastomers, such as natural rubber or silicone, but still has enough elasticity to form an airtight seal. While butyl rubber will break down
when exposed to agents such as certain solvents, it breaks down more slowly than comparable elastomers. A durable Butyl Rubber Sealant can be
used on metal windows and doors, downspouts, chimney flashings, shingles, skylights, siding, below-grade applications, and marine usage above
the water line. Interior or exterior use with easy solvent clean up.
Urethane Sealants
Urethane construction sealants have excellent adhesion to a variety of substrates and have good movement capability. They cure to a soft, flexible
but durable rubber. They are used to seal vertical and perimeter expansion joints on buildings and horizontal joints in parking garages and
sidewalks. The main disadvantage of urethane sealants is their lack of resistance to UV. Urethane-based sealants are one of the most commonly
used sealants in both construction and transportation markets because of their long service life, excellent flexibility (which allows joint
movement), and good adhesion to many substrates. In construction, polyurethane sealants are used in the manufacture of insulating glass windows
for high-performance joint sealing in concrete and metal buildings, and for sealing roofing membranes. They are very popular for homeowner DIY
(do-it-yourself) and OTC (over-the-counter) sales to builders, for blocking drafts and air leaks around foundations, windows, and electrical
outlets. In original equipment manufacturer (OEM) auto and truck production, urethane sealants are used for windshield glazing and in the aftermarket
for installing replacement windshields. Urethanes are also used for seam sealing in body repair shops. Chemically, a polyol, usually a polyether
polyol, reacts with a diisocyanate (such as toluene diisocyanate) to form polyurethane. For sealant use, a prepolymer, partially reacted polyurethane
with an excess of isocyanate groups, is formed; the reaction completes upon application. Most urethane sealants are formulated as single-component
types where the prepolymer is blocked by one of a variety of moieties to avoid pre-cure. After the sealant is applied, available moisture in
the air causes the unblocking of the prepolymer and the reaction proceeds to completion. In two-component urethane sealants, the prepolymer
and polyol are reacted, often with the use of a catalyst, just before application.
Thermoplastic Sealants
Thermoplastics can be repeatedly softened by heat and then hardened, or set by cooling, which allows parts to be injection-molded or thermoformed
and scrap to be reprocessed. Thermoplastic or hot melt adhesives can be repeatedly softened by heat and then hardened, or set by cooling,
which allows parts to be removed or repositioned during assembly. Most hot melt adhesives are solvent-free thermoplastics that melt
or drop in viscosity above 180°F, and then rapidly set upon cooling. They are used in a variety of manufacturing processes, including bookbinding,
woodworking, construction, product assembly, and box and carton heat sealing. Hot melt adhesive technology stemmed from the previous use
of molten wax for bonding. Thermoplastic systems were introduced to satisfy performance needs. Typically, a pure hot melt system will not have
the heat resistance of two-part, catalyst or thermoset adhesives. Hybrid hot melt systems are available that exhibit a degree of reactive
curing. Polyethylenes, polyamides and ethylene-vinyl acetates are common types of hot melt adhesives. Heat activated adhesives become sticky
or tacky when warmed, and are used in contact or PSA-type applications. One of the most recent developments in the thermoplastic field
is a product which really falls somewhere between the thermoplastics and the elastomers. This sealant is made in two grades. One is used in
non-critical areas such as highways and runways and the other is used in areas such as warm up aprons and taxiways where jet-fuel spillage is
involved. This material has many advantages over most thermoplastics in that is manufactured and delivered as a liquid. Most of the others are
solids which have to be melted down. This particular product still has to be heated but since it starts out as a liquid it can be heated quite
rapidly. There are a few rubber asphalt type materials on the market which do not require heating before being used. Some of these are two part
material and others are single component materials ready for use. Logically, cold poured seals on should not be included under the heading of
thermoplastics since the term "thermoplastic" indicates a softening under heat and the ability of be melted a number of times without
adverse effect. In addition to the thermoplastics and the cold poured or cold-applied materials, there are also the so-called butyl rubbers.
These are no-skinning sealants made from poly-isobutylene and poly-isobutylene. They are compounded with resins, oils, fillers, solvents, and
pigments to produce a wide range of sealing compounds. The butyl rubbers are nonoxidizing and almost non-curing since they remain tacky for
an extremely long period of time. In this respect, they resemble the non-hardening mastics. These sealants are used more as caulking compounds
than as joint sealers.
EPDM Sealants
EPDM Rubber Sealant is a two-component (catalyzed) EPDM rubber compound, which can cure at ambient temperatures (55° F and above). It can be
used as a caulk, surface sealant, or to create a gasket and can be applied over rubbers, metals, masonry, fiberglass and wood. The compound
is thixotropic so it can be applied by brush, spatula or refillable caulk gun. It is designed for applications requiring a flexible material
having a broad temperature tolerance, chemical and solvent resistance range. The cure mechanism requires exposure to air on one side. If forming
a gasket, allow material to cure on one surface before assembling with a mating surface that is impervious. The compound contains 35 % volatiles
so the cured dry film will only be 65 % the thickness of the applied wet film. Do not apply wet films greater than 50 mils thick because the
rubber will not be able to cure through to the center. EPDM Rubber Sealant will experience 35 % shrinkage of the applied film and should only
be used where such a dimensional change is acceptable. Otherwise it is suitable for use in extreme environments and will tolerate:
- Temperature ranges from minus 60 to +300 degrees F
- High humidity, live steam and total immersion
- High salt concentrations
- Alcohols and polar solvents
- Many acids up to 50 % concentrations
- Caustic solutions to a pH of 12
Sealant should not used in places where it will come in contact with oils, fats, waxes, or aliphatic solvents such as Mineral Spirits, Heptane,
Hexane and similar solvents.
Neoprene Sealants
Neoprene Sealant is a one component sealant that mainly consists of neoprene rubber and synthetic resin. This product is specially formulated
for water-proofing, dust-proofing, and hermetically sealing of containers, cabins, buses, mobile homes, and refrigerated vans. It is suitable
for sealing normal and small joints and all engineering material surfaces. Neoprene is a fast cure sealant. After cure, it provides a tough,
flexible bond, excellent elasticity, and water resistance.
Features
- High durability and weatherproof
- One component , no mixing required
- Good adhesion on metals, plastics, glass, aluminum, and many engineering materials.
- Permanently flexible under stress, normal expansion and compression.
- Easy to gun
- Fast cure system
- Can be painted
Typical Uses
- Sealing joints in containers especially steel containers
- Sealing some parts of automobiles, buses, and other vehicles
- Sealing joints of zinc and slate roofs
- Suitable for joints with low movement after curing.
- No need to smooth the surface. Sealant is self-leveling, thus the surface will have a good finish automatically after curing.
Note: Neoprene sealant is not suitable for high joint movement applications and some types of foam substrates. The organic solvent containing
in the sealant can swell the foams before the sealant is fully cured. Pretest is required before use with foam materials.
All of the above sealants are suitable for use with skylight installations, depending on the specific needs of each location. It is up to the
skylight manufacturer or architect to decide which sealant or combination of sealants is best, depending on the conditions and requirements
for each installation.
