Sealant Solution

July 1, 2005
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Pre-cured silicone sealant available for renovation and new construction applications



Over the years, many types of liquid-applied sealants have been used in the construction industry. These "wet sealants" include acrylics, polyurethanes, polysulfides, silicones and other technologies. While these wet sealants have been used successfully for many years, the advantages of pre-cured joint sealants are bolstering their popularity. Pre-cured joint sealants are produced by extruding material similar to wet sealant and allowing it to cure to an elastomeric product in a controlled manufacturing environment. They are packaged in cured form, often in rolls, instead of in liquid form (tubes, pails, etc.) like standard wet sealants. Pre-cured joint sealants are installed using a thin layer of wet sealant on the edges as an adhesive to attach the material to the substrate it is sealing.

Several basic types of pre-cured joint sealants are used in the market today, ranging from extruded polyurethane and polysulfide to silicone-rubber extrusions. Each type offers unique chemical and physical characteristics. Silicone pre-cured joint sealants have been positioned in the forefront of construction applications for several reasons. First, silicones have excellent aging characteristics and are resistant to UV light and weathering, which gives silicone a much longer effective life span than organic materials like polyurethanes and polysulfides. Because silicones do not degrade when exposed to the elements, it is possible for manufacturers to produce very thin material (1-2 mm). Thin pre-cured joint sealant minimizes expansion and contraction forces on the substrate and creates the more pleasing appearance of a flat profile. In addition, the movement capability for silicone pre-cured joint sealant is as high as +200%/-75%, significantly higher than any type of wet sealant. This combination of high-movement capability and thin material gives pre-cured silicone sealant the ability to handle multi-directional movement. Additional advantages of silicones over other materials include a wide operational temperature range and better resistance to color fading. Because of these benefits, silicone pre-cured sealants are the materials of choice in the construction industry today.

Two primary types of pre-cured silicone joint sealant are available for use in construction applications: high-consistency silicone rubber (HCR) and ultralow-modulus RTV extrusions. HCR was developed with a high-compression set for use as compression seals; these materials have been successfully used in Europe as expansion joint seals for over 25 years. RTV silicone extrusions have a much lower compression set and a considerably lower modulus of elasticity than HCR extrusions. This results in greater flexibility and extremely high movement capability. In addition, RTV silicone extrusions offer better tear resistance and tear-propagation resistance than HCR extrusions. Resistance to tear propagation is a very important characteristic; high resistance to tear propagation can keep a small hole in the material from developing into a major product failure. Unlike HCR extrusions, RTV silicone extrusions will not tear completely, even if the material is punctured.

Over the past decade, pre-cured silicone sealants have been used mainly for renovation and remedial construction applications. One example of a typical application for pre-cured silicone sealant is the repair of failed standard-sealant joints. When pre-cured silicone sealant is used to repair a failed standard-sealant joint, there is no need to remove the old sealant. The pre-cured sealant is simply applied over the old joint using a thin layer of silicone sealant adhesive on each side of the pre-cured sealant extrusion.

This system saves time and reduces overall project cost, two of the most important advantages that pre-cured silicone seals offer. Depending on the application, there can be a significant reduction in overall project expense by using pre-cured silicone sealant instead of traditional wet sealant. Labor costs are greatly reduced since pre-cured silicone sealants remove several labor-intensive steps from the process. For example, old sealant does not need to be cut out when using pre-cured silicone sealant. In addition, the substrate does not need to be mechanically abraded to ensure the complete removal of the old sealant.

Also, pre-cured materials do not need to be tooled after installation like wet sealants. This is another step that can be avoided when using pre-cured sealants for renovation projects. Because labor typically accounts for the majority of total cost in a construction project, the overall cost of a project can be greatly reduced by using pre-cured silicone sealant.

This system for repairing failed sealant joints is especially useful with soft and sensitive substrates, such as EIFS and natural stone. With these types of soft building materials, removal of the old sealant will damage the substrate and ruin the integrity of the joint. Since the old sealant and substrate are not disturbed during application, pre-cured silicone sealants are also beneficial in applications where the old sealant and/or substrate may contain hazardous materials, such as asbestos or PCBs.

Wet-applied sealant bridge joints have been used in the past for butt-joint applications where the joint depth was not adequate to achieve the required 1⁄4" of bond area to the substrate. This situation is common to applications such as leaking aluminum window systems. These wet-applied sealant bridge joints, which are still used today, are difficult to install and almost never achieve a consistent and uniform joint. In addition, since the industry-standard thickness for a wet-sealant bridge joint is 6 mm, and pre-cured silicone sealant is typically produced at a thickness of 1-2 mm, the pre-cured silicone sealant is more aesthetically pleasing. Furthermore, due to the thin sealant-adhesive layer required to attach the pre-cured sealant to the building substrate, the adhesive cures rapidly and joint deformation during cure is minimized. This is particularly evident when comparing a cure time of several hours for the adhesive used with pre-cured silicone sealant to a 6 mm thick wet-sealant bridge joint, which can take several weeks to cure completely. These factors, along with ease-of-application, are causing pre-cured silicone sealants to replace many wet-applied sealant bridge joints.

Another situation where pre-cured silicone sealants are used instead of wet-sealant joints occurs when joint width is not adequate to handle the joint movement. This occurs frequently in buildings that are lacking an ample number of expansion joints on the exterior substrate, causing the joints to expand and contract beyond the movement capability of the wet sealant. Another example is found in window perimeters where the opening does not leave adequate space around the window for a working sealant joint. Because the sealant adhesive is only used on the edges of the material, the pre-cured silicone sealant system creates its own joint width to handle the movement experienced by the substrate in these situations.

Besides remedial work over failed sealant in expansion joints and butt-joint applications, pre-cured silicone sealants are used successfully in many other applications, including the following.

  • Window perimeter seals
  • Aluminum window systems
  • Roofing and parapet seals
  • Curtainwall seals
  • Skylights
  • RV, marine and transportation seals
  • HVAC system seals
  • Fillet beads for showers/tubs

As pre-cured silicone sealants have become more accepted by the construction industry, manufacturers have made an effort to continually improve and expand their product lines. Today, there are many more standard sizes and colors available, as well as custom colors and widths. Custom-designed materials can be produced with one or more notches in the extrusion. These notches allow pre-cured silicone sealant to follow complex bends on a building in applications such as inside and outside corners, parapet caps, and window mullions. Materials with surface textures designed to match the appearance of EIFS, stucco and many other surfaces are also available.

Pre-cured silicone sealants have been successfully used in renovations and remedial construction applications for many years, and are becoming accepted by the industry as a viable alternative to removing failed sealant. Consequently, more contractors, consultants, architects and specifiers are realizing the benefits of using pre-cured silicone sealant, allowing for applications in new builds as well. For example, it is thought that the use of pre-cured silicone sealants could lead to a change in basic joint design in new construction projects.

As leaders in the industry begin to realize the impact that cost savings and product performance can have, it is expected that the market share for pre-cured silicone sealant will continue to grow. The scope and magnitude of the use of pre-cured silicone sealants in construction and other industries will greatly depend upon the collaboration of contractors, specifiers, architects, consultants, and manufacturers.

For more information, contact Sealex Inc., 8850 Moeller Drive, Harbor Springs, MI 49740; phone (231) 348-5020; fax (231) 348-5255; e-mail jbakus@sealexinc.com; or visit http://www.sealexinc.com.

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