The construction industry continues to evolve as new materials are used to improve the longevity and strength of structures. Additionally, the constant push to increase productivity drives innovation and enables introduction of new ways to resolve skilled labor shortages, along with incorporating efficient materials for modularizing and fabricating structures off-site. This trend has given rise to modular and prefabricated solutions. Cross Laminated Timber (CLT) is a key contributor to modular panels. The benefits of CLT panels are:

  • Faster on-site assembly
  • Higher quality construction
  • More standardized building

The recent advances in building materials increase the number of components mass produced and brought to construction sites. This results in buildings being erected more quickly and quietly with far less waste. Another driving factor relates to reducing environmental impact of new construction. Beyond energy efficient new construction, a focus on zero carbon emissions allowed the growth of CLT for large construction design. This goes beyond the materials once they are on-site. It includes the efficient manufacturing of modular panels. One example is the Carbon 12 project. At 85-feet tall, it is the tallest CLT building in the United States (as of January 2020). The popularity will continue to grow as CLT manufacturers are able to provide a natural and innovative alternative to steel and concrete. Cost-effective and renewable, mass timber construction is becoming a popular platform for owners, architects, engineers and builders.

Evaluating Building Material Options

Building materials continue to evolve to meet ever-changing demands from regulators, owners and consumers. Reducing environmental impact while keeping people safe is the goal. Each material – wood, steel and concrete – have advantages and unique characteristics. While concrete and steel have historically been viewed as the most robust and durable materials, CLT brings new options to designers, contractors and owners. Substantial benefits of CLT use include the following:

  • Offers high strength, structural simplicity and a lighter environmental footprint than concrete or steel in construction – CLT is carbon negative and uses wood exclusively from sustainably managed forests
  • Enables quicker installation, reduces waste and improves thermal performance for buildings
  • Adapts to the project demands – thickness and length can be adjusted, as well on-site construction duration is a few days versus weeks and months with concrete and steel construction
  • Generates very little waste – CLT components are shipped for just-in-time scheduling and arrive on-site as a kit, which results in minimal storage requirements

Given the variety of CLT dimensions, it offers flexible design options. The key is the adhesive and how it bonds with the wood panels to produce prefabricated elements. The adhesive also contributes to the structural performance to deliver compressive strength similar to concrete. As the industry continues to adopt CLT, owners want to understand more about the performance and protection it provides to large structures.

Interior of condo constructed of cross-laminated timber. Photo courtesy of Kaiser+Path

Increasing Adoption of Engineered Wood for Large Structures

With the increased demand for sustainable design, building materials have evolved to reduce the direct and indirect impact on the environment. During the construction lifecycle, buildings use energy, water and raw materials; generate waste and give-off emissions. Cross-laminated timber is gaining in popularity because it is easy to install and generates almost no waste on site. It offers high strength and structural simplicity necessary for cost-effective buildings, as well as a lighter environmental footprint than concrete or steel.
Constructed of several layers of kiln-dried lumber, CLT is stacked in alternating directions, bonded with structural adhesives and compressed to create a panel. The adhesive used in CLT applications needs to meet stringent product standards and must be certified to ANSI standard. These adhesives are designed to balance the ratio between open time and pressing time and provide maximum flexibility for the manufacturer.
There are three manufacturing methods for CLT – Cold Press with Formaldehyde Adhesive, Radio Frequency (RF) press and Cold Press with Formaldehyde Free Adhesive. Each method can support three- to seven-layer panels.  The primary differences between each method involve:

  • Manufacturing set up and resources
  • Adhesive type
  • Energy use

As CLT manufacturers continues to transition to more efficient manufacturing processes, adhesive is critical to adopting more efficient and sustainable processing. Henkel’s LOCTITE® HB X Purbond is a one-component polyurethane adhesive.  It is free of solvents and formaldehyde and meets the most rigorous strength and emissions guidelines for CLT. Henkel’s LOCTITE® HB X Purbond is designed to work with Cold Press manufacturing without the need for respirators and the moisture curing process does not require heat and reduces energy use.

LOCTITE® HB X Purbond is designed with variable open times between two and 70 minutes.  The CLT manufacturer can select the open time – the interval between adhesive application and jointing – that best fits their operation. The formaldehyde-free formulation meets the latest specifications in mass timber construction for healthy indoor air quality in residential premises.

Collaborating to Deliver Success

Cross Laminated Timber manufacturing is adaptable to each project. The panel thickness and length fit specific building uses and environments.  In new building, CLT keeps construction on site to a few days. CLT components may be shipped for just-in-time scheduling, arrive on-site as a kit of parts which minimizes storage requirements.

Henkel works with a variety of CLT manufacturers, contractors and architects to develop solutions to achieve more functional and sustainable buildings.  Contact us to learn more how we can help you with your CLT project.

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