Acrylic foam structural glazing tape used for structural glazing on the Movenpick Hotel, Frankfurt, Germany. Courtesy of 3M

Dr. Choi concluded the results indicated that the acrylic foam structural glazing tape was a good medium for the mounting of glass curtain wall panels. The performance of the panels mounted using the tapes were as good as the panels mounted using a conventional structural silicone sealant. The test mock-up had been subjected to the high temperature of 158°F as well as the low temperature of -13°F, and the performance of the tape-mounted units compared favorably with the silicone-mounted units and perhaps better (moisture condensation was observed on the silicone-mounted units but not on the tape-mounted units).

He reported that the structural strength of the tape in bonding the glass panels to the metal frame was shown to be extremely good. Test pressure (suction) of more than twice the design pressure was applied onto the units. In one case (the second test sequence) there was no failure. For the other case, the first test sequence, the glass fractured but delamination was not observed on the four edges of the glass panel.

Durability. Another major concern in the use acrylic foam tape in any construction process is its durability. Various types of durability tests have been carried out, all with good results, reports Dr. Choi. Findings include:

• After acrylic foam tape was aged for more than 5 years at 150°F (65°C), the roll yielded 92 percent retention of peel adhesion. (Peel adhesion (ASTM D3330) is a measurement of the bond strength to the substrate as well as the strength of foam.)
• In accelerated weathering tests, the tape bond was subjected to heat, humidity and concentrated ultraviolet light exposure. The bond strength did not deteriorate below its original performance level, even after exposure of 7,500 hours in a weatherometer (an apparatus in which specimen materials are subjected to high intensity UV light, cycling heat and humidity.)
• Outdoor weathering tests typically demonstrate about 100% bond strength retention after 2 to 5 years aging cycles in the hot, humid climate of Florida, the hot, dry and very sunny climate of Arizona and the cold to hot extremes of Minnesota on bonds to aluminum, glass, PVC and painted metal. In Minnesota, the tape showed a constant performance after 5 years of outdoor aging.
• Long-term continuous submersion in water and brine (2 weeks, 10 years) caused no significant reduction in adhesion to substrate (tape submerged in water).

Dr. Choi concluded that the results of the series of vigorous tests showed that the performance of acrylic foam structural glazing tape was as good as the conventional structural silicone sealant for use in curtain wall construction. It performed as well for air infiltration and water penetration tests and sustained a high pressure loading in the structural load test, well beyond what the joint was designed for.

Design Guidelines
For tape area calculations, the following guidelines can be used:

Dynamic Loads (with dead load support of glass) For dynamic tensile or shear loads (such as wind loads), a design strength of 12 pounds per square inch (psi) or 85 kPa is used for acrylic foam structural glazing tape. This design strength provides a safety factor of five and was established based on material property testing as well as ASTM dynamic load testing for curtain wall applications.

Static Loads (no dead load support) For static tensile or shear loads (such as dead weight loads, snow loads, and other long-term loads), a design strength of 0.25 psi (1.7 kPa) is used for acrylic structural glazing foam tape. This means four sq in of tape per one pound of load should be used to support static loads. This guideline provides a safety factor of at least five.

Dynamic and static load calculations should be performed on unsupported deadload structural glazing applications. The calculations resulting in the wider tape width should be used as the appropriate tape width for the application. No dead load support should only be considered for monolithic glass applications. Always consult the tape manufacturer when considering an application with no deadload support.

Application Guidelines
Each acrylic foam structural glazing tape application should be reviewed on a project specific basis by the tape manufacturer. Application guidelines should be based upon adhesion test results generated by the tape manufacturer, who should provide application guidelines to be followed during the bonding process.

Typical Application Guidelines

• For maximum bond strength, all non-glass surfaces should be thoroughly cleaned with a 50/50 isopropyl alcohol (IPA) and water mixture to remove contaminants. Some surfaces may need additional treatment with a primer. Glass surfaces should be cleaned and then treated with a mixture of an IPA, water, and silane solution (silane is a chemical compound that serves as a stabilizing coupling agent) prior to tape application. A properly mixed silane solution is used to promote adhesion of acrylic foam structural glazing tape to the uncoated glass surface. Glass is hydrophilic (water loving) in nature and may lead to performance issues over time in humid or wet environments due to water vapor undercutting the bondline and interfering with normal adhesion forces. A silane solution treats the glass surface creating a hydrophobic surface that will act to protect the tape bondline.



• Ideal tape application is accomplished when temperature is between 70°F and 100°F (21°C and 38°C). Initial tape application to surfaces at temperatures below 60°F (16°C) is not recommended. However, the use of a primer may lower the minimum application temperature.



• Bond strength is dependent upon the amount of adhesive-to-surface contact developed. Firm application pressure develops better adhesive contact and helps improve bond strength. Generally, this means that the tape should experience at least 15 psi (100 kPa) in roll down or platen pressure. • After application, the bond strength will increase as the adhesive flows onto the surface. At room temperature, approximately 50 percent of the ultimate strength is achieved after pressure application, 90 percent after 24 hours and 100 percent after 72 hours. The use of a primer may greatly accelerate the bond strength build rate.

On the market since 1980, acrylic foam tape is found in a multitude of applications in a cross section of industries around the globe. But it has only recently become available in the U.S. as an effective alternative to structural silicone and spacer tape for commercial curtain wall applications. Available outside of the U.S. since 1990 for structural glazing, it has been used in over 3,000 curtain wall projects in South America, India, Europe, and Asia. As architects, curtain wall fabricators and contractors discover its features and analyze potential production cost and time savings, acrylic foam structural glazing tape for structural glazing should become a viable choice for specifiers of curtain wall glazing systems.

Acrylic foam tape is two-sided, pressure-sensitive, closed-cell acrylic foam. Used within and outside the construction industry, it is designed to bond to a wide range of substrates including most metals, glass, many plastics, composites, sealed wood, paints, and powder coatings. Suitable for both indoor and outdoor applications, it typically replaces liquid adhesives, spot welds, screws, rivets, and other mechanical fasteners. Its many applications range from fastening panels to horse trailers in order to achieve durability and a smooth surface, for attaching flex electronic circuit boards and bonding ceiling panels to suspension frames at Chicago's O'Hare Airport.

In the early 1980's, applications broadened in the commercial construction industry to include permanent bonding and sealing of architectural metal panels to a variety of surfaces including frames, stiffener attachments, I-beams, and metal cladding. Among the many applications from Australia to Brazil and the U.S. to the United Arab Emirates, are high profile examples where acrylic foam tape replaced screws, rivets, welds, and silicones. One is the Frank Gehry-designed Walt Disney Concert Hall in Los Angeles, completed in 2003, where the stainless steel panels were bonded by tape to stiffeners and aluminum framework. Another U.S. application is on the $355 million Dearborn Center in Chicago, IL, completed in 2003, and designed by Ricardo Bofill Taller de Arquitectura of Spain and DeStefano & Partners Ltd. of Chicago. Considered to be one of the most technologically advanced buildings in the world at the time, acrylic foam tape was used to bond stiffeners to the exterior metal trim cladding.

Liberty Memorial Museum, Kansas City, MO. Architect: ASAI Architecture, 2006. Structural glazing with acrylic foam tape conforms with the interior luminous white drum curtain wall. Courtesy of 3M

Examples on other continents include Skidmore, Owings & Merrill's Adelaide Convention Center in South Australia, opened in 2001, where acrylic foam tape bonded aluminum composite panels to a galvanized frame. In Dubai, U.A.E., aluminum composite panels of W.S. Atkins & Partners-designed Burj Al Arab Hotel, opened in 1999, were bonded by acrylic foam tape to the framework to resist high wind loads in this harsh and warm environment.

Acrylic Foam Tape as Bonding System for Curtain Walls

Glazed curtain walls are one of the most commonly used fenestration systems for commercial buildings. Fabricated on site or delivered pre-assembled, glazed curtain walls are classified by how they are built. This is in contrast to windows, which are classified by how they operate. In addition to different construction methods, curtain walls are also distinguished by both the glass selected and the glazing system used for weatherproofing and to hold the glass in place.

Glazing systems support the glass in the frame and seal the dissimilar materials from the weather. Structural glazing is a system of bonding glass to a building's structural framing members utilizing a high strength, high performance product (conventionally, silicone sealant) specifically designed and tested for structural glazing. In structural glazing applications, dynamic wind loads are transferred from the glass, by the structural glazing product, to the perimeter structural support.

Structural glazing is conventionally achieved by using a spacer adhesive tape to hold the insulated glass unit off the frame. Structural-grade silicone sealant is then shot into the space between the frame and glass. The dimensions of the spacer tape govern the thickness of the silicone to be used, and are calculated according to wind load requirements. Common spacer tape dimensions are 1/4 inch thick by 1/2 inch wide.

Acrylic foam structural glazing tape replaces both spacer tape and structural silicone for structural glazing. A single product comprising a solid adhesive construction, it serves as the primary bonding agent and a secondary sealing agent. Spacer tape is sometimes referred to as "structural glazing tape" and should not be confused with acrylic foam structural glazing tape.