Whether one is trying to replicate ornate trim work from the 19th Century or trying to seamlessly replace exterior molding on a building constructed in the 1970s, polyurethane millwork products can be the answer. Widely used for both historical and contemporary commercial and residential renovation projects, these plastic components have gained in popularity since their introduction several decades ago.
With the advent of polyurethane millwork in the ’70s, high-density polyurethane’s durability and versatility made it competitive with more traditional materials for applications both inside and out. Additionally, these polyurethane products can resist moisture, humidity, warping, splitting, splintering, insect infestation, and extreme temperature changes.
SPECIFYING THE POLYURETHANE SPECTRUMPolyurethane products, which come with a factory-applied ultraviolet ray-resistant topcoat, may be painted with any good quality latex or oil-based paint. They also accept decorative faux finishes well, such as marbleizing, washing, and texturizing. (These can be especially appealing on such products as round and oval ceiling domes, wall niches, and moldings.)
Polyurethane products range from louvers and moldings to columns and decorative millwork, with products in both structural and non-structural categories, such as window/door trim, gable vents, porch posts, and balustrades. From ornate brackets to faux beams to door pediments, polyurethane manufacturers have a wide variety of products ideally suited for both commercial and residential projects when it comes time to think about renovation work-or subtly replacing damaged components made from more traditional materials.
The high-density material is manufactured using a two-component rigid polyurethane foam system and has a closed-cell structure that can resist water penetration and absorption. (For more information, see sidebar on “Making Polyurethane Products.”)
Rigid polyurethane’s durability is due to its status as a thermoset material-in other words, once the reaction has taken place to form the polymer, it cannot revert to its original components with just heat being applied. This means increasing the temperature of the material-within reason-does not cause it to melt or significantly lose its structural properties. Generally, rigid polyurethane foams have good dimensional stability (including resistance to volume change in extreme ambient temperature conditions) due to the strong polymer network created when the foam is produced. Additionally, polyurethane foam has a low coefficient of thermal expansion and contraction, which can make it suitable for many temperatures.
With polyurethane, each piece has a consistent quality and finish, so there are no wasted materials and onsite installation is easily accomplished. Compared to decorative trim products made from traditional materials, polyurethane millwork generally has lower overall product and installation costs. Furthermore, as polyurethane products require no sanding, priming, or sealing, they can also allow for labor savings. While raw material costs for the material’s traditional counterparts may be lower than polyurethane foam, labor costs for product installation and maintenance of these traditional products is generally higher.
CAPABILITIES OF POLYURETHANE MILLWORKArchitects and contractors interested in using polyurethane products for renovation projects can find support on the Web sites of various polyurethane manufacturers. Specially created design programs exist from all major suppliers, with several offering design configurators, CAD programs, and architectural binders. Additional resources include industry-standard calculators (for radius, rake, and bevel miter cuts) and the ability to create elevations and assemblies.
Polyurethane millwork pieces can replicate intricate patterns on ceiling medallions or contain smooth lines on moldings. For renovation projects, one of the material’s chief assets is the ability to gain highly detailed, authentic looking reproductions of historic products. Heavy, ornate, plaster ceiling medallions can be replicated in polyurethane pieces weighing less than 1 pound (0.45 kg). For those projects requiring the “look” of traditional materials, many manufacturers offer stainable polyurethane moldings containing authentic wood grains.
The closed-cell structure of polyurethane products can make them suitable for high humidity areas, such as bathrooms, kitchens and laundry rooms. Wall niches, moldings, and brackets are popular in these rooms because they neither warp nor twist when exposed to excessive moisture. Throughout the rest of the building, polyurethane products can be found as window and door trim, ceiling domes, faux beams on ceilings, and as one-piece mantel surrounds. Low-maintenance polyurethane shutters, louvers, and entryway surrounds on the exterior of projects are generally available in dozens of styles complementing all major designs.
From refurbishing classic millwork in restaurants, offices, and healthcare centers to replacing balustrade systems in college dormitories, nursing homes, and hotels, polyurethane is selected for a wide variety of commercial projects worldwide. What once may have been an arduous task of specifying historically accurate reproductions of moldings can now be accomplished relatively quickly. Polyurethane companies offer architectural profiles in everything from uncluttered to ornate designs. Suitable for both interior and exterior use, there are hundreds of decorative polyurethane millwork options including corbels, ceiling domes, acorns, wall niches, and brackets.
Available in lengths up to 16 feet, polyurethane moldings range from simple 2-inch tall pieces to intricate built-up combinations more than 1 foot high. Hundreds of profiles exist to replicate an array of designs and styles. Some of the most popular moldings include dentil profiles, cornice-and-cove, crowns, chair rails, and window/door trim. More elaborate egg-and-dart, crown leaf, ribbon-and-bow, Florentine, and scalloped molding profiles are also available. Special collections of styles, including Victorian, arts-and-crafts, southwest, and contemporary moldings and millwork, are also available, as well as accessories, including miterless corners, plinth blocks/rosettes, keystones, and molding divider blocks.
Whether one is trying to replicate a molding pattern from an 1812 Federal-style inn or create a unique design element of a mallard for the entryway of hundreds of hotel rooms, polyurethane manufacturers have the ability to support custom design needs. Once patterns and designs are finalized, special molds can easily be created at the production facility and pieces formed to fit the project’s exacting requirements.
Architects and contractors can take advantage of polyurethane’s custom capabilities by requesting fabricated pieces for door entries and windows. The in-house fabrication shop at polyurethane production facilities can customize pieces for oversized openings or with specific design preferences. Specifying the mixing and matching of pieces from a product catalog can result in the manufacturer creating customized window and door enhancements, saving job site time and labor.
One innovation applauded as a time saver by both specifiers and installers is the polyurethane eave vent system, which acts as both a decorative molding profile and a functional vent that can prolong roofing shingle life. Structures using these systems often contain functional louvers-a combination of polyurethane louvers featuring slats with steep 45-degree angles that also include non-corrosive screens to help keep insects out while allowing airflow.
LIMITATIONS AND BUILDING CODESMany polyurethane products are created solely for decorative use and have little structural integrity. The exceptions are porch posts, balustrade systems, and columns constructed with fiberglass, PVC and/or steel support interiors. (Since there is no distinct advantage of any of these structural materials when used in conjunction with polyurethane, the support material is determined by the application and manufacturer.)
Some companies conduct independent testing by certified laboratories for load-bearing capabilities on these structural products. While many manufacturers follow International Building Code guidelines for testing of rail systems, there are no specific guidelines for load-bearing capabilities on structural products. Some manufacturers test these pieces to a load at which the amount of force being applied stops increasing and levels off. From that number, a safety factor of 1.75 to 2.00 is used to come up with the load capacity.
Specifiers will find most polyurethane products produced by manufacturers can safely be used in accordance with rulings from the International Code Council’s I-codes and the National Fire Protection Association. Some balustrade systems meet the National Building Code’s 1993 Criteria (1615.8.2 Guard Design and Construction and 1618.104.22.168 In-Fill Areas) when assembled according to manufacturer guidelines.
These codes are met based on the way the balustrade system is assembled, not necessarily on the polyurethane product itself. Manufacturers assemble the balustrade systems according to the installation guidelines they share in their catalogs and then test these same systems to check that the pieces comply with code rulings.
While polyurethane millwork products are suitable for varied climates, they should never be stored for long periods in extreme heat as they can expand and contract slightly when heated and cooled. Should the products be exposed to intense heat for extended periods of time, they can become distorted and warp. Most polyurethane millwork can withstand temperatures of about 140 degrees F (60 C), but prolonged exposure to temperatures beyond 200 degrees F (93 C) can result in the deterioration of the polyurethane foam’s physical properties. One of these aspects may be the blistering of the piece’s surface-an incident especially prevalent when the product has been painted a dark color that absorbs the heat. However, since polyurethane foam is a thermoset plastic, it does not melt in extreme temperatures-the worst-case scenario is deterioration and possible blistering.
As with most building products, polyurethane pieces should acclimate for approximately 24 hours in their installation environment prior to application. Due to the temperature warping described above, a special consideration for polyurethane millwork is that it should never be specified in an area subject to solar temperature buildup, such as behind a storm door.
While some manufacturers are currently working toward meeting the flame-spread tests in ASTM International E 84, Standard Test Method for Surface Burning Characteristics of Building Materials, most polyurethane millwork products are not specifically formulated for fire resistance. Check with individual manufacturers for flame-resistance restrictions and special product orders that meet Class 1 ratings. In all cases, local building codes should be consulted and followed when using polyurethane or any other building product in a project.
CASE STUDIES AND EXAMPLESWhile the primary use of polyurethane products is for decoration, there are many cases where millwork pieces are specified to solve challenging design problems. For example, to help create a stately exterior for a Providence, R.I., assisted living center, the design team specified an expansive array of polyurethane balustrades, corbels, and detail work on the building exterior. The pieces transformed the three-story structure and added both the necessary structural and decorative accents to replicate an old-time mansion. In a similar situation in St. Louis, a designer challenged with replicating cracked and decaying plaster molding in a historic hotel ballroom turned to polyurethane. The manufacturer was able to create a perfect historic match to the existing millwork. In an unusual twist, the polyurethane product was added to the room in various sections while original plaster pieces were also left in place. The result is a space using both plaster and polyurethane millwork with differences that are difficult to see.
To make life easier for his beachfront customers, a builder in Avalon, N.J., surrounded the exterior of dozens of windows with polyurethane molding and trim that are continually exposed to sea air and salt spray. Exposure to such elements would mean repeated scraping and repainting on traditional trim products. However, the use of polyurethane helps minimize opportunities for rot, decay, and degradation caused by harsh weather.
One reason why polyurethane balustrade systems are so popular is because the balusters are reinforced with fiberglass or aluminum, while rails and newels have PVC reinforcements and porch posts have steel reinforcements. The balustrade pieces are made with non-corrosive parts that are hidden to provide a clean, classic appearance from any angle-they can maintain their design aesthetic without the heavy demands of ongoing maintenance.
There can also be other advantages-for Toledo, Ohio’s Owens Illinois building, the design team consulted to update the look of the structure was challenged with replacing outdated can lighting. However, since replacing the lights meant disturbing asbestos and gypsum wallboard, the team decided upon a stepped-trim polyurethane molding that simply covered the old fixtures and eliminated the need to remove the asbestos. Additional complementary polyurethane moldings were used on the building exterior to tie it together with the interior design. W&C
Sidebar: Making Polyurethane products:To manufacture a piece of precision-molded polyurethane millwork, a company starts by hand-carving an original master design out of wood. Next, silicone is poured around the original wood master to create a production mold. A nozzle dispenses liquid polyurethane into the production mold, which has been pre-painted with a barrier coat of UV-resistant primer.
A lid is then placed over the mold, trapping the liquid polyurethane inside. The mold is placed under pressure and the polyurethane quickly expands to fill it, creating an exact duplicate of the original master. Once set, the molded part is removed from the production mold and checked for quality.
Next, the high-density polyurethane piece is treated like wood-each piece is hand-inspected, sanded, and cut to finished size. The piece is then primed and ready for packaging, before a final inspection.