Skip to main content
U.S. flag

An official website of the United States government

Post-fabrication preservative treatment of CLT


Andrew Shahan
Mark Denavit
Adam Taylor
Jeffrey Lloyd



Publication type:

Paper (invited, offered, keynote)

Primary Station(s):

Forest Products Laboratory


paper in AWPA proceedings


Cross laminated timber is becoming a popular manufactured building material that offers a safe and environmentally friendly alternative in large building applications that were previously limited to concrete and steel. Preservatives are often applied to wood products to protect them from decay and extend their service life. However, CLT panels are typically not treated due, in part, to a lack of efficient and effective methods for treating large panels and a lack of information on what impact the treatment process has on the panels’ mechanical properties. In this work, a variety of CLT panels were obtained from different manufacturers and constructed with different species and layup options to evaluate the double-vacuum preservative treatment method, which has the potential to accommodate large panels. Small samples were cut, edge-sealed, and double vacuum-treated with a borate preservative solution. Samples were then tested in rolling shear following standard procedures. Preservative retention, penetration, and dimensional changes varied among each species and consisted of retentions above, near, and below standard values presented for solid sawn lumber. The double vacuum treatment method effectively penetrates around laminations but negatively impacts the mechanical properties. The reduction in mechanical properties could be acceptable in some cases, depending on wood species and their treatability, and therefore warrants more research to optimize the double vacuum method. This work will help to provide higher-durability CLT panels, and thus increase the potential applications and service life of this exciting new technology.


Shahan, A.; Denavit, M.; Taylor, A.; Lloyd, J.; Mankowski, M.; Kirker, G. 2021. Post-fabrication preservative treatment of CLT. In: Proceedings of the 117th annual meeting of the American Wood Protection Association. Vol. 117. Nashville, TN. July 27-29, 2021. Birmingham, AL: AWPA: 128-131.

Publication Notes

  • We recommend that you also print this page and attach it to the printout of the article, to retain the full citation information.
  • This article was written and prepared by U.S. Government employees on official time, and is therefore in the public domain.