Caulk and Sealant Guide
Which caulk and sealant will fill your inside
Caulks and sealants are used in metal
construction to fill gaps and cracks. They are a barrier to prevent
the passage of air, water, moisture, gas, noise, dust and smoke.
Generally representing less than 1 percent of a building's cost,
they are extremely important to the water/airtightness of the
building. For this reason, correct selection based on properties
and applications is important to the weathertightness of the
Caulks typically are associated with filling gaps that do not
experience much expansion or contraction, and are used to prepare
for painting. They are rigid and inflexible. In metal construction,
caulks are used on the interior filling gaps between drywall,
windows and trim, or casework before paint is applied.
"The word caulk is an old boat building term and is sometimes
used by manufacturers as a general purpose term for acrylic
materials with little or no movement capability," says Jason Bakus,
vice president of Sealex
Inc., Harbor Springs, Mich. "Acrylic latex caulks are normally
paintable with water-based or solvent-based paints, but are not
generally used in metal construction due to the amount of shrinkage
they experience as well as their tendency to crack over time. Most
manufacturers refer to their elastomeric sealing products as
Sealants play a vital role in metal construction and act as a
seal between metal and other exterior materials to form a barrier
for infiltration or exfiltration of moisture, air and airborne
"Sealants are used when there is a high likelihood of expansion,
contraction or movement between the metal substrates and are
designed with polymers allowing flexibility," says Dr. Roger Moore,
director of marketing and product support manager, Novagard Solutions Inc.,
Cleveland. "Sealants like Novaflex metal roof sealant serve in a
number of roles in metal construction including structural glazing
as well as any application where a seam between two metal
substrates come together and a flexible watertight seal is
Sealants are used in many different applications in metal
construction ranging from standing seams, metal end laps, roof
penetrations and curbs to expansion joints, roof to wall
transitions, roof steps and height changes, ridge expansions,
gutter seams and many others.
Metal panels create a couple of distinct challenges for
sealants. "First, metals expand and contract with changes in
temperature, so joints with metal panels definitely experience
dynamic movement," says Bee Miller, manager of market development,
Architectural Specifications, Franklin International-
Titebond Adhesives and Sealants, Columbus, Ohio. "Additionally,
because many of the most common paints and surface coatings in the
industry are designed to last for a long time, some of the
specialty coatings can be challenging to bond to and maintain a
strong bond with."
Silicone sealants provide excellent joint movement capabilities
(ASTM C920, Classes 25, 35, 50 and 100/50) up to 50 percent.
Silicone sealants offer superior adhesion to common building
material substrates including glass, aluminum, wood, steel, vinyl
and masonry. However, a primer is recommended for use on some
substrates, particularly cementious substrates. "Documented studies
on the long-term performance of silicone sealants have been
published by the major manufacturers and indicate performance in
excess of 20 years in terms of resistance to moisture, oxidation,
high temperatures and UV exposure," says Moore. "These products are
not recommended in high-traffic areas where abrasion may cause
degradation of the surface. Application temperatures of silicone
sealants far exceed those of inferior polymeric sealants and often
range as low as -20 F to +140 F and also have large service
temperature ranges such as -40 F to +400 F."
Most silicone formulations are not paintable; however, modified
silicone sealants may be paintable. Silicone sealants may stain
some porous substrates such as concrete and some natural stone
substrates. Silicone sealants are well known for their ease of
application and clean up. They are typically 100 percent solids, or
non-solvent type, and easily meet VOC environmental regulations,
are not flammable and clean up easily after use.
Pre-cured silicone sealants-or silicone membranes as they are
sometimes called-are commonly used in a variety of metal building
applications. "Because of their ultra-high movement capability (200
percent plus) and unique properties, they are used for sealing high
movement areas on metal building applications such as expansion
joints, roof to wall transitions, roof height change details,
joints between new and existing buildings, ridge applications and
others, including a variety of repair applications," Bakus says.
"Pre-cured sealants are bonded to metal and other substrates using
a separate adhesive and require no fasteners."
In the past, there has been some concern with compatibility of
some silicone sealants with metals such as Galvalume and
galvanized. "This issue was with acetoxy (acid-based) cure
products, which are no longer used in metal construction
applications," Bakus says. "Neutral cure silicone sealants have
been used in metal construction applications for many years and do
not pose corrosion problems with these metals."
Not used as commonly as silicones, polyurethane sealants offer
superior joint movement capabilities and have good adhesion to most
common building substrates. Polyurethanes for the metal building
industry are generally one-component, moisture-cure sealants
designed to skin and cure rapidly. Premium polyurethanes are
specified due to their superior UV resistance and long term
Builders should select a polyurethane with a minimum of 50
percent joint movement: +/- 25 percent. "Selection of polyurethane
can depend on substrate," says Mark Platz, industrial business
manager, ITW Polymer Sealants
North America, Irving, Texas. "With today's specialized
coatings, not all polyurethanes adhere the same to all surfaces.
While some can adhere to wet surfaces or even underwater, others
may require a primer or pretreatment depending on the substrate.
Premium polyurethanes remain flexible with life expectancies
reaching 20-plus years depending on exposure to extreme elements.
They cure to a tough, durable, elastic consistency with excellent
cut-and-tear resistance, come in a variety of colors, and most are
"With service temperatures from -40 F to 200 F and elongation
availabilities of 500 to 600 percent polyurethanes are frequently
requested by the metal building contractor. Polyurethanes are
available in gun grade (cartridges) and can be non-sag or
self-leveling. They are easy to tool for an aesthetically clean
finish. When applied in close proximity, neutral cure silicones can
prevent polyurethanes from curing. This problem does not exist if
either product is allowed to cure prior to application of the
Typically polyurethanes exhibit good compatibility with the
metal and masonry surfaces; however, "They should not be used in
structural glazing applications with contact with glass," cautions
Moore. "These sealants can be formulated to give aboveaverage UV
resistance and may be paintable. Some formulations contain solvent,
and shrinkage due to solvent evaporation must be taken into
consideration." Some health professionals recommend wearing
respirators during application.
The most common solvent-based synthetic rubber sealants are
acrylic. They are most often used in perimeter sealing or other low
joint movement applications. They may need special handing due to
flammability and they have environmental considerations.
"Solvent-based sealants typically have good durability and can be
applied at below freezing temperatures," says Miller. "They are
typically paintable but only after a seven- to 14-day full-cure
period. They are flammable in the wet state, can be difficult to
tool due to short open times, and can produce a significant odor
during application and cure time."
Non-skinning, non-drying (Butyl) sealants are the primary
sealant in standing seam roofs and the joints of insulated metal
panels. Designed to stay soft and flexible, they ensure a positive
seal when jointing roof or wall panels. They should exhibit a
non-stringy consistency with easy cut-off characteristics for clean
"Butyl sealants are easily pumped into the female leg of
standing seam roof panels and are compatible with all current types
of paints and coatings used by today's rollformers," says Platz.
"This product does not cure like standard pumpable sealants,
allowing for movement, self-healing, and can offer a life
expectancy equal to that of the roof system. This sealant requires
an application temperature range of 10 F to 120 F and a service
temperature range of -60 F to 200 F. This is a non-curing sealant,
therefore it is not paintable, is supplied in white or off-white
(color) and is used in conjunction with mechanical fasteners."
Within the past few years, hybrid sealants such as modified
silicone (MS) (silyated polyether) and SPUR (silyated polyurethane)
have come onto the construction market and claim the best qualities
of both silicone (UV resistance) and polyurethane (paintability).
Hybrid sealant use in metal construction is minimal at this time,
but is growing.
"Common hybrids used are tested to withstand +/-50 percent
expansion/contraction," says Miller. "Hybrid life expectancy is
generally very good. Appearance and UV resistance are very good,
and they are typically paintable if discoloring occurs from
weathering over time. They handle and tool nicely and have low to
When selecting caulks and sealants, evaluate all performance
characteristics to determine the optimum sealant against the cost.
Discuss your sealant applications with the manufacturer to
determine the best product for each application as there is no one
product for all applications. Compatibility with the substrate may
require different curing mechanisms.
Sidebar: Tale of the tape
Butyl tapes are most commonly used to seal the side- and
end-laps of standard single-skin panels. Butyl tape is a
non-curing, 100-percent -solids compound that is a highly rubbery,
tacky sealant which remains permanently flexible. Butyl tapes are
packaged in rolls or strips with a removable release liner for easy
handling and application. Butyl tapes are soft and pliable and are
designed to compress between overlapping panels to form a positive
seal. With elongation values greater than 1,000 percent, butyl
tapes can last for 25-plus years and are compatible with all
painted metals including but not limited to Galvalume-, Zincalume-
and Kynar-coated products. With application temperatures between -5
F to 120 F and service temperatures from -40 F to 200 F, they are
routinely used in all climates. Although butyl tapes exhibit
excellent UV characteristics, proper application would not require
them to be exposed to direct sunlight. Also, antimicrobial
additives are used by some manufacturers to inhibit the growth of
molds and mildew.
Mark Platz, industrial business manager, ITW Polymer Sealants North
America, Irving, Texas