NovDec98

Page 15

Composite Technology Fiberglass-reinforced plastics (FRP) are used increasingly in exterior architectural applications. Cost effectiveness has made FRP popular in restoration projects in addition to new construction of hotels, casinos and amusement parks, the types of big projects that comprise the fastest-growing segment of the $50-$70 million architectural fiberglass industry.

"It's been a long, hard sell to convince architects and preservationists that FRP can realistically duplicate the aesthetics of original ornamentation," said Charles Wittman, president of American Fiberglass Corp. (Copiague, N.Y.).

Architects who select FRP for exterior restoration of deteriorating historic buildings know it can effectively replicate the appearance of most traditional materials, such as sheet metal, terra cotta, stone, wood, and cast iron. Functionally, FRP offers design versatility, utilizing its high strength, light weight, durability and Class 1 fire retardance.

Advances in two components - gel coats and adhesives - have helped make FRP competitively attractive. Material suppliers have developed structural bonding adhesives and gelcoats that dramatically address weathering and color change as demonstrated by accelerated weatherometer testing.

These current-generation gel coats, the specially formulated and pigmented polyester resins that form the surface of molded parts, provide enhanced water resistance and weatherability. They minimize heat distortion, shrinkage, and cracking. And the fading and yellowing that have given FRP a bad name in the past are virtually eliminated.

A patented molecular technology developed by Ferro Corp. (Plymouth, Ind.) is formulated with a lower styrene content, which reduces surface shrinkage and prerelease problems and helps molders meet stringent new environmental requirements, according to Kamana Jigweva, Ferro's new product research and development manager. It also has improved spraying characteristics that allow more of the gel coat to get to the mold, reducing overspraying and waste.

The advanced high-strength adhesives now readily available include the family of methacrylates. These adhesives facilitate the production of large, complex shapes that can be molded as individual components and structurally assembled into complete units without the need for mechanical fasteners and difficult back-up laminate joints. It has taken quite a while to convince fabricators of the reliability of the adhesives. Adhesive-bonded joints have proven to hold, in Wittman's words "like grim death."

RESOLVING WEIGHTY EXTERIOR ISSUES

A Mediterranean-style public building constructed in Old San Juan, Puerto Rico, in 1924 had a heavy problem. Over the decades, the massive, ornate wooden cornice that projected 6 ft from the masonry walls had lost its battle to gravity.

In 1997, Fibertech (Pendleton, S.C.), a manufacturer of architectural parts, reproduced the entire cornice using fiberglass and fire-retardant polyester resin. Measuring 9-ft long by 6-ft deep, the cornice was mounted to structural stainless steel beams, which were attached to the masonry wall with about 200 decorative fiberglass brackets 3-ft high by 6-inches wide.

The challenge of the project, explained John Wilson, Fibertech president, was matching the parts to each other and to the uneven original masonry. The ornamental details were varied and complex and the dimensions of the original buildings were inconsistent.

DETAILS, DETAILS

The multi-level domed cupola on the Helmsley (office) Building in Manhattan provides another notable example of architectural composite capabilities. constructed in the 1920s with lightweight concrete and copper cladding over a steel frame, the cupola had sustained serious water damage.

Seal Reinforced Fiberglass Inc. (Copiague, N.Y.) was able to replicate the one-of-a-kind structure from a one-eighth section of the original octagonal cupola.

Chopped strand mat and woven roving were hand laid up to fabricate some parts. Balsa-core sandwich construction was used to fabricate flat surfaces. Urethane foam core was used to make some areas soundproof and watertight. The cured parts were sprayed with Class 1 fire-retardant and surfaces were then painted with gold-colored urethane base coat, followed by a clear urethane top coat.

The original steel structure was repaired or replaced. The copper cladding was repaired by reframing with wood, and attachment hardware was installed.

The 500 FRP parts required to replicate this complex cupola included square and round column sections, railing sections, inner and outer domes, arches, orbs, wall panels and pinnacles.

Questions? Email us or
call 707-552-3500

Last updated: 09/21/06