Real Wood Veneer: The Sustainable, High-quality Product Choice

Veneer profile wrapping and laminating boosts wood's green quotient, reduces costs and encourages design creativity.
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Core Materials

Depending on the performance requirements of the finished product, the substrate or core might be made of the following (or many combinations of the following): softwood, hardwood, MDF, LVL (an engineered product composed of multiple layers of thin wood assembled with adhesives) as well as aluminum, vinyl or fiberglass. Manufacturers have recently gained success wrapping veneer over recycled steel. As steel can be an oily metal, the manufacturer's challenge will always be to determine and monitor the material's surface friction and the oil content/residue of the steel core profiles, and to formulate an appropriate polyurethane adhesive in order to create a reliable and long-lasting bond.

Though cores can be made of virtually any smooth, stable material, finger-jointed softwood cores are generally recognized to be the most popular and economical substrates for mouldings and millwork.  This is consistent with wood resource management principles that require every harvested tree to be used to its maximum economic and environmental value, as softwood cores can be fabricated from lower grades of wood that might otherwise be rejected due to knots or other imperfections, or even scraps of solid wood or veneer, because the profile wrapping covers any defects in the core material.  

This is particularly important in light of the fact that billions of cubic feet of useable low grade lumber are currently under-utilized. If this waste wood could be transitioned to the supply chain, harvesting burdens would be reduced on forests, and billions of tons of embodied carbon dioxide sequestered, eliminating methane and other gases emitted by decomposing wood.   Research indicates that up to 50 percent of underutilized or waste wood material could be converted to serviceable solid wood products, with the remainder available for processing into byproducts - a situation where a 100 percent utilization rate could be achieved. These statistics indicate that an enormous amount of wood products can be manufactured without any additional timber harvesting.

The low-grade pine used for most substrates comes mainly from longstanding managed forest lands that can easily sustain harvesting this wood. The solid clear products being replaced typically come from natural forests or forest land that is being managed for significantly longer rotations. Using the faster-growing, shorter-rotation pine reduces pressure on natural forest lands and on less plentiful species. The 50-1 resource efficiency ratio achieved in profile wrapping allows rarer tree species to also be utilized at an increased level of sustainability. Further, because low-grade pine stands on shorter rotation actually yield valuable products, there is less pressure to convert these managed forests to other non-forest purposes, enabling them to continue to provide such benefits as carbon sequestering, wildlife habitat, soil and water retention and filtering, etc.

Extruded aluminum wrapped in white oak was the ideal solution for vertical blinds at London's King's College.

Photo courtesy of Contact Industries

 

Despite its considerable attributes, however, a soft wood substrate is not always the answer. Finger-jointed hardwood cores (which often are made from post-industrial recycled wood waste) are periodically specified where some concern is expressed for very high-traffic areas subject to damage or abuse. MDF, in all its product types, is frequently specified, but due to weight and possible exposure to moisture, is best selectively placed in strategic areas or products. Alternate material substrates including aluminum, PVC, fiberglass and steel are often used for specific purposes, including ceiling panels and window and door components.

In applications where product weight is an issue, aluminum may function as an appropriate core material. During a recent remodel, London's King's College used profile wrapping in creating vertical Venetian blinds. While designers liked the look of white oak, it was too heavy and too costly to be deployed in a window covering. The college opted instead for extruded aluminum wrapped in white oak veneer for a dimensionally stable, fire-rated, aesthetically pleasing solution. Some 1,210 pieces totaling 92,503 lineal feet of vertical blinds were shipped with pieces delivered to exact measurements in made-to-order lengths.

Adhesives

The best veneered profile wrapped products are bonded with a polyurethane reactive moisture curing hot melt adhesive (PUR). The result of government regulations concerning VOC emissions and industry concerns regarding the quality of adhesion, PURs contain no solvents, offering "green" strength and superior bond performance. Accepted in many industries as a replacement for mechanical fasteners, PURs are applied to a substrate in a thin line that sets virtually immediately and becomes rigid within minutes. The reactive hot melt actually chemically crosslinks after 72 hours so it will not lose adhesion regardless of whether it is exposed to extreme temperatures, either hot or cold. Formaldehyde-free emulsion polymer isocynate (EPI) exterior adhesives are used in flat lamination.

Substrate is profile wrapped with veneer on the cell, sanded and goes straight into a carton for shipment.

Photo courtesy of Contact Industries

 

Veneer Wrapping: From Design to the Production Process

Designers envision mouldings and millwork items in their projects from a number of perspectives, including:

  • Finished profiles they believe aesthetically represent the design intent.
  • Appropriate species and protective top coat finishes.
  • Fit, form and function needs.
  • Balanced integration with other materials on the site, including windows, doors, flooring, ceilings, tile, wall coverings, fire-related requirements, etc.

To avoid product substitution, designers should call out profile wrapped or flat laminated products on project plan documents.

Responding to designers' project plans, manufacturers identify the size and location of the component, and suggest the appropriate substrate and veneer material for the product size, application and location. The manufacturer translates the profile of the component and/or trim designed by the architectural professional into a shop floor manufacturing plant CAD approval drawing. Upon review and approval, an order is placed, and the manufacturing process begins. The substrate is molded to the pattern of choice, and wrapped in the desired veneer.

Prepping the Veneer.A good profile wrapping process begins with premium veneers that are climate controlled to prevent cracking and are processed from a random width and length flitch to make the most efficient use of the resource. This process also allows any minor defects to be cut out so that a clear product will result, preserving the resource and saving time during installation.

For optimum results, the veneer must be properly prepared in a multi-step process that includes the following:

  • The appropriate clear lumber slicing blank is selected and inserted into a water-filled autoclave; a "vacuum" is drawn and water introduced into, and allowed to penetrate all the lumber's cells.
  • The "soaked" slicing blank is introduced to the horizontal veneer slicer.
  • After the large draw knife slices the veneer from the blank to the appropriate thickness, it is introduced to a dryer where moisture is dropped gently to 9 percent.
  • The veneer is finger-jointed together into lineal rolls for fleece backing and sanding.
  • The back of the veneer is fleeced in a lineal process with heat, adhesive and pressure. The 25 or 50 gram thickness fleece is a nylon material used to bind together the veneer's fiber, and make it more pliable for profile wrapping, enabling it to be wrapped around curves, without changing its physical appearance. The backer should be the proper weight to allow the product to wrap without cracking.
  • The veneer is sent through a four-head sander and sanded with a 180-grit finish to achieve optimum smoothness prior to adherence to the core material.

 

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Originally published in GreenSource
Originally published in May 2009

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