Adhesives

A variety of adhesive types are
available for many different
applications, including insulation attachment, insulation-fitting fabrication, and facing. Adhesives are available in water-based, solvent-based, hot
melts,
reactive-cure, pressure-sensitive, and aerosol formulations. These adhesives can be applied through
numerous methods, including brush, spray, trowel, and roll coater. When selecting an adhesive, the insulation
type, service-temperature limits, application method, and required adhesive strength should all be considered. Refer to the adhesive manufacturer’s
product
selection guides for assistance in choosing adhesives for specific uses. In all cases, regardless
of the type of adhesive used to secure the insulation, it is important to prepare the surface being adhered to. It
must be free of dirt, rust, loose particles, and oil. Wiping the surface with denatured alcohol is often
recommended. Ambient and surface temperature are also important considerations when selecting an
adhesive. When considering ambient temperatures, it is essential to factor in the temperature over the entire curing time. The surface being bonded to
must also
be considered. Steel (coated or painted), plastic (such as polypropylene), or others, may require
special preparation work or adhesives.

For attachment and fabrication, rigid insulations will usually require thicker, high-bodied adhesives capable
of filling small gaps, while flexible insulations such as fiberglass, mineral wool, or elastomeric use thinner
adhesives with a higher coverage rate. Attachment or fabrication of impermeable insulations will require contact,
pressure-sensitive, or reactive-cure adhesives to avoid trapping vapors. Water-based adhesives are not recommended. When using contact adhesives, it is
important
to coat both surfaces with a thin coat of adhesive (a thin coat is better than a thick coat),
and to allow the solvents to evaporate before combining the 2 surfaces. This may vary with installation conditions (temperature and humidity). When
using pressure-sensitive adhesives, it is important to apply pressure to ensure the adhesive is wetted out between the 2 surfaces being adhered. As the
installation
temperature gets colder, the amount of pressure to wet out the adhesive increases.

Other specialty adhesives include cryogenic adhesives for very cold operating systems (down to -320°F), and high-temperature inorganic adhesives for
hot work (up to 800°F). When used for attachment, most adhesives are used in conjunction with mechanical fasteners.

Duct-Liner Adhesives

Duct-liner adhesives include water
and solvent types as well as pressure-sensitive adhesive and hot melts. They
can be applied in a sheet metal shop
either as part of a coil line or on
fabrication tables. Typical duct-liner
specifications require 2 forms of
attachment; generally, weld or stick
pins and an adhesive are used. On coil
lines, the adhesive is often water based
to allow for immediate weld-pin
placement without concern for flash
fire. Water-based adhesives do not work
well with closed cell foam duct-liner
materials because the water cannot
evaporate. Hot melt, spray adhesives, or
pressure-sensitive adhesives are often
used on these products.

Reinforcements for Cements and Mastics

Reinforcing fabrics for cements and mastics are critical to prevent cracking over seams or areas of movement, and to improve the overall strength of the finish. They come in a variety of types
and sizes. The reinforcement chosen must be of the correct type and size, and be compatible with the mastic or cement to ensure proper function. Refer to the mastic or cement manufacturers’ product
data sheets for compatible reinforcements. Fiber fabrics include open-weave fiberglass, synthetic fiber meshes, woven canvas, and fiberglass cloth. Mastics are typically reinforced
with 10″ x 10″ open-weave cloths for most applications. Heavier duty 5″ x 5″ mesh cloths are sometimes used with heavier coats of mastics. Reinforcements should always be embedded within the wet
mastic or cement and be fully covered. All seams in the fabric should be overlapped by a minimum of 2 inches to avoid the potential for cracking.

Sealants

Sealants can be broken up into the following general categories:

• Duct sealants
  • Sheet-metal sealants
  • Duct-board sealants
• Flashing sealants
• Joint sealants

Duct Sealants

Duct sealants come in a variety of formulations. Typically the sealant is a high-bodied water or solvent-based formulation applied by brush or cartridge gun. UL-181 A-M for duct board
and UL-181 B-M for flexible and rigid metal duct give standard requirements for duct sealants that may be used to specify them. Metal ducts should also
meet the Sheet Metal and Air conditioning Contractors National Association (SMACNA) pressure standards for the duct system being sealed. Refer to the duct sealant manufacturer’s
product data sheets and material selection guides for more information.

Flashing Sealants

Flashing sealants are used to seal insulation terminations, penetrations, and protrusions that occur around valves, gauges, and other areas where the insulation is broken. They may also
be used to seal metal-jacketing seams. Flashing sealants protect the exterior of the insulation system from the ingress of liquids or vapors. The flashing sealant must be compatible with
all the surfaces it comes in contact with, including the insulations and insulation finishes. It should be applied per the manufacturer’s instruction in order to create a
watertight seal.

Joint Sealants

Joint sealants are used to seal the longitudinal and circumferential butt joints of rigid insulation against moisture penetration. Joint sealants are
of
particular importance in cold-temperature systems to lock out water
vapor penetration between blocks of insulation. Joint sealants are made using high solids and are available in a
variety of types. The joint sealant should remain flexible after application to allow for movement in the insulation
system without cracking or splitting. Selection of the proper joint sealant will depend upon the operating
temperature at the point where the sealant is applied, the insulation type being sealed, and the finishes being
applied over the top of the insulation. Refer to the manufacturers’ product data
sheets and product selection guides for more information on the selection and application of joint sealants.

Other Accessory Products

There are a wide variety of additional accessory products required for successful installations of
mechanical insulation, including:

• Securements
  • Studs and pins
  • Staples, rivets, and screws
  • Clips
  • Wire or straps
  • Self-adhering laps
  • Tape
• Flashing
• Stiffening
• Supports
  • Heavy-density insulation inserts
  • Pipe-support saddles and shoes
  • Wood blocks and dowels
  • Pre-insulated pipe supports
• Caulking
• Expansion/contraction devices

These accessory products are readily available from a number of vendors.