Polyurethane adhesives and polyurethane sealants are finding increasing uses within the housing construction industry for various reasons. The material offers good adhesion to numerous substrates, such as concrete, wood, plastic, and glass due to its elasticity and structural properties. These features, along with continued technological improvement, have widened the number of polyurethane adhesive and polyurethane sealant applications in residential projects.
Originally, polyurethanes found use in the manufactured housing market and modular homes. The material’s elasticity provided the necessary flexibility and structural integrity, allowing the manufactured home to be moved onto the site without nail popping or joint breakage. Currently, a two-part polyurethane adhesive is the predominant adhesive used for attaching the ceiling gypsum wallboard to the truss rafters. In volume units, this is one of the largest applications for two-part polyurethane adhesives in the housing construction market.
A hidden advantage of the two-part polyurethane adhesive product is its allowance for a multiple cure system. For instance, one catalyst can work nearly instantly to build viscosity and resist slumping on vertical surfaces, while a slower secondary curative allows for longer open time and then final cure. Thus, the two-part urethane system can be custom-formulated to fit the desired working environment.
Polyurethane adhesives applications and advantages
One type of project where polyurethane adhesives are employed is modular construction, which is built on the same lines as manufactured housing, using the same bonding systems. (This construction type represents less than three percent of all housing in the United States, with the majority being classrooms, day care centers, and field offices.) Perhaps the largest use of any polyurethane adhesive is the moisture curable system. Its usage joins sub-flooring to floor joists in combination with nails. This type of adhesive bonding is also used in manufactured housing for both floors and exterior walls.
Recent uses for moisture cure polyurethane adhesives can also be found in finish carpentry. Finish carpenters use the material for adhering the corner joints of trim framing for doors and windows. This application prevents the expansion and contraction caused by humidity and temperature of the corner joints, potentially eliminating call-backs to the builder.
Finish carpenters have continued to find uses for this type of polyurethane adhesive, such as building staircases that command stronger, non-squeeze steps and railing systems. There are also other incidental uses for this adhesive in the installation of various cabinetries and other finish trimming. An example would be the need to place decorative spacer boards between cabinets or between a cabinet and wall. The polyurethane adhesive helps prevent separation cracks in the cabinet facing due to seasonal changes in the wood as it contracts and expands.
While the focus of this article has thus far been on polyurethane adhesives, polyurethane sealants have also become a mainstay in the construction industry. The newer silyl-terminated polyurethanes have enhanced the properties and usefulness of one-component, moisture-cured, paintable urethane sealants to fit the energy-efficient trends of the public.
Forecasting future functions
So what does the future hold for polyurethane adhesives and polyurethane sealants? An analysis of today’s trends in the housing construction market provides a basis for polyurethane adhesive usage estimation. The major trends in the construction industry that may impact this usage are:
- Continued increase in methods and materials improving energy efficiency.
- Older generations demanding low maintenance and high quality.
- Warranties on new homes (and the expense of costly call-backs) have made the builder more aware of polyurethane adhesives’ benefits.
- Increased use of various types of engineered lumber and joists.
- Prefabrication of components built off-site.
- Greater demand to build homes that can withstand natural forces, including earthquakes. (In some coastal regions, building codes have begun to embrace higher standards.)
While none of these trends directly promote the use of polyurethane adhesives, most are likely to indirectly advance the use of polyurethane adhesives and polyurethane sealants within the housing industry.
In many residential construction applications, it is expected some type of mechanical fastener will continue to be used, but adhesives could be a new source for application. For instance, controlled studies have demonstrated polyurethane adhesives used with mechanical fasteners in the framing of a house can provide strong resistance to the damaging high winds of hurricanes and tornados.1 The flexibility of the adhesive is the key to providing greater resiliency against these exterior forces. In fact, some builders in the Pacific Northwest already use adhesives for joining the roof sheathing to the roof rafters, so as to help stabilize the roof against high winds.
Wrapped or bent lumber that must be pulled into position requires a mechanical fastener to hold it in shape, but engineered lumber can be more conducive to using polyurethane adhesives because it is dimensionally stable and flat. Composite lumber used in building decks will benefit easily from the use of structural urethane adhesives, as these materials can eliminate the need for hole-drilling and/or special mechanical fasteners. In this case, the polyurethane adhesives can prevent surface damage caused by the use of a screw or nail.
More stringent building codes, increased use of prefabrication, engineered lumber, energy efficiency, and higher warranties all will play key roles in even newer applications for polyurethane adhesives. Particularly, polyurethane adhesives are expected to benefit greatly due to their structural—yet flexible—properties and the potential ease of application.
Source: www.greenbuildingsolutions.org
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