Nine Benefits of Using Polyurethane Instead of Wood
Today’s new home construction, remodeling projects and historic renovations all have one thing in common. They require the use of high-performance building materials that are:
high-performance building materials that are:
Strong, reliable and durable
It is only natural to see myriad materials vie for supremacy in renovations as well as new home construction. Polyurethane millwork qualifies is another one of these attractive building products. It delivers the aesthetic appeal of crisp detail. Depending on the application, it can simultaneously preserve and enhance property values and curb appeal. Look closely, and you’ll find polyurethane present in a wide variety of architectural elements, including entryway enhancements, louvers, shutters, dentil blocks, cornices, brackets, column wraps, dormers and window headers.
Choosing Polyurethane over Wood
There are two basic kinds of high-density polyurethane: open cell and closed cell. The latter variety is used for molding, cornices, louvers, decorative ceiling beams, ceiling domes, columns, mantels and balusters. Available profiles blend with the architectural elements of many different types of home, including Victorian, Federal, Georgian, Southwest, Arts-and-crafts and Ultra-modern.
1. Closed-cell durability
High-density polyurethane is a material widely used in home construction and renovation. The closed-cell nature of the material makes it resistant to the hazards of inclement weather and a host of adverse environments. Polyurethane is highly resistant to:
Closed-cell polyurethane is hydrophobic, so it won’t absorb water. Therefore, exterior polyurethane balusters and columns resist swelling and absorption when exposed water. The higher density skin is also highly resistant to oil and grease. It does not degrade when inadvertently exposed to a wide range of chemical compounds. The closed-cell nature of the substance also helps it resist both dirt and stains. This often translates into longer painting/staining intervals and reduced maintenance costs.
In addition to its impressive impact resistance, polyurethane also offers attractive tensile properties and excellent tear resistance. The toughness of polyurethane is enhanced by its high resilience and good skin density.
Mold, mildew and fungus
Resistance to mold, mildew and fungus is particularly attractive to builders working in tropical and sub-tropical climates common across the southern U.S. However, they are also a threat anywhere vulnerable exterior surfaces, like exposed end grain wood surfaces, stay wet for extended periods, particularly during the warm summer months. Inside a home, mold growth on wood and other vulnerable materials can compromise the health of its occupants.
So-called “wet rot” is typically caused by mold growth. FEMA asserts that “Mold growths, or colonies, can start to grow on a damp surface within 24 to 48 hours.” Rotting wood is often soft and spongy. As an affected area dries out, it often cracks or crumbles. Paint adhesion suffers, and structural integrity is often compromised.
Some areas of the country are more vulnerable to another enemy of wood. Dry rot is caused by several species of fungi that break down down essential parts of wood building materials. In high concentrations, the spores of the wood-eating fungi appear orange in color. The term is somewhat misleading because the process of decay typically requires at least some moisture at the outset.
Polyurethane millwork is an excellent alternative in areas vulnerable to termites, ants and other insects. Frequently, insect infestations are more than unsightly. For example, a wood baluster compromised by an infestation may become unsafe.
Long-term exposure to the sun’s ultraviolet rays has long been the enemy of exterior building materials. It is possible to enhance outdoor color stability through the addition of UV inhibitors to the pigment prior to the extrusion process. Application of a UV-resistant, factory-applied topcoat is another possibility.
Finally, there are applications in home construction where the electrical insulating properties of high-density polyurethane are an advantage.
With polyurethane, it is possible to choose formulations with different densities, typically ranging from three to 50 pounds per cubic foot. The density of polyurethane millwork is approximately 15 to 20 pounds per cubic foot. However, since the molding process typically creates a higher skin density than core density, it delivers durability in excess of what one would expect from its overall density.
High-density polyurethane is so versatile that it is used in recreational products, machinery, transportation equipment, medical equipment, office equipment and appliances. High-density polyurethane is used to fabricate parts weighing a few grams to more than one ton.
In home construction, it is used for much more than millwork. It is also used in energy-efficient ICF wall construction and foam-core doors. Lesser densities are used to insulate walls and attics.
With wood, it is possible to choose different densities — hardwood vs. softwood, and old-growth vs new growth. However, old-growth resources are increasingly scarce, and the supply will only diminish over time. When it comes to wood, the use of anything other than new-growth softwood runs counter to modern sustainability initiatives.
3. Aesthetic benefits
With polyurethane millwork, designers and architects enjoy a host of creative opportunities. When custom profiles are required, lead times are typically quite modest. It is possible to create almost any kind of millwork using designs, molds or drawings. The molds themselves can be fabricated using CAD/CAM. Or, it is possible for skilled craftsmen to machine them using regular woodworking tools.
When ornate or highly decorative designs are the goal, polyurethane is typically more economical than wood. Polyurethane millwork will also accept appealing faux finishes like texturizing, washing and marbleizing.
4. Shrinking and swelling
One of the most significant challenges with wood millwork is the potential for 1) shrinking in low-temperature and/or low-humidity environments, and 2) swelling in high-temperature and/or high-humidity environments. Also, wood that is not fully and properly kiln-dried may shrink and crack over time. Even well-caulked gaps may open up, leaving end-grain vulnerable to moisture infiltration.
Minimal movement under extreme conditions promotes the retention of joint and seam structures. Many parts of the country experience temperature extremes. Many communities that see -20 F temperatures in the winter witness triple-digit heat in the summer. Therefore, expansion and contraction of exterior construction materials is an important consideration. With polyurethane, stresses on joints and seams are modest. It is also abrasion-resistant across a wide range of temperatures.
5. Load-bearing capacity
The impressive weight-to-strength ratio makes it an attractive choice for some balusters and balustrades. Polyurethane also rates well in terms of compression and tension. Even when it changes shape under a heavy load, it demonstrates a significant capacity to resume its original shape when the load is no longer present.
6. Paint adhesion
Polyurethanemillwork typically arrives pre-primed and paint-ready. Paint, caulk and spackle readily adhere to the surface.
Excellent paint adhesion is important for a number of reasons, including chipping. When paints chips off of wood molding, repairs are not always that simple. Often, it’s necessary to complete at least three steps: sand, prime and paint. The resilience of polyurethane makes it less prone to chipping. At impact, the material absorbs some of the force, minimizing chipping. Minimal peeling minimizes maintenance, and it extends the time between painting and re-painting.
Polyurethane’s sustainability is increasing in part because its lifespan advantage reduces future demands on non-renewable resources, including old-growth wood. Also, as polyurethane building products are increasingly recycled, the advantage they have over the use of non-sustainable old-growth timber increases. There are numerous kinds of mechanical recycling, including re-grinding, powdering, thermoplastic reprocessing, re-bonding and compression molding. There are also additional alternatives like feedstock and chemical recycling.
Plantation-grown, finger-jointed softwood is an option for millwork, but it lacks the qualities that attract builders to the old-growth alternative. The fast-growing Monterrey or radiata pine is another alternative, although it is more commonly found in the Southern Hemisphere from Australia to South America. Limited stands appear in the far western part of the United States.
8. Ease of installation
Of course, labor costs are a significant part of many a construction or renovation project. With polyurethane millwork, labor savings accrue in a variety of ways. Polyurethane moldings often come in longer lengths that reduce cutting, fitting and installation time. Flexible moldings follow the contour of imperfections in wall and ceiling surfaces. Excellent flexibility also allows for quick installation along curved walls and window bays.
Exterior installations can be performed across a wide range of temperatures in excess of 50 degrees F. For best results, it is ideal to acclimate polyurethane millwork to installation temperature for at least 24 hours. Since it is a thermoset product, polyurethane millwork is very temperature-resistant. Still, it is wise to avoid exposure to temperatures exceeding 140 degrees F. Ongoing exposure above 200 degrees F can alter the physical characteristics of high-density polyurethane.
Contractors comfortable with wood millwork typically find that switching to the polyurethane alternative is pretty straightforward. Use traditional woodworking tools to shape, route and cut polyurethane.
9. Manufacturing process
Since polyurethane molding is made by pouring liquid resin into a mold, single-piece construction is often possible where wood requires a multi-piece fabrication process. For example, an elaborate crown molding may require the lamination of multiple pieces of wood, driving up costs in the process.
Other Competing Materials
Various forms of millwork are also fashioned from fiberglass (FRP), plaster, polyvinyl chloride (PVC), medium-density fiberboard (MDF), flex glass-reinforced gypsum, and polystyrene.
The plastic polymers in PVC are impervious to moisture, but its slick surface may be tricky to paint. Although the density of PVC is similar to that of oak, it tends to look more artificial than natural. Also, PVC is typically available only in more basic shapes.
Flex, as its name suggests, is a bendable, rubbery material commonly used on more highly curved walls and window bays.
Polystyrene lacks the crisp appearance of polyurethane. The lightweight material is easy to cut and install. Because it is vulnerable to moisture intrusion, glass-reinforced gypsum is only used in select interior applications.
Polyurethane delivers the ornate and elaborate designs historically associated with plaster, but without the weight. For example, a post in Green Building Solutions asserts that “Some heavy, ornate, plaster ceiling medallions can be replicated in a urethane plastic piece weighing less than 0.45 kg (1 lb).”