Cross-laminated Timber (CLT) is increasingly being used in residential and non-residential construction around the world, and some of these areas are at high risk of biodeterioration. Addition to moisture management of construction, preservative treatment of CLT may be needed to prevent decay and termite attack in the area. Pressure treatment being most reliable, is not feasible due to the large dimensions of CLT panel. Also, fabrication of CLT using pressure treated laminas has some difficulties about re-drying cost and physical damages such as distortion and delamination. Non-pressure treatment called “deep penetration treatment” has increased their share on treated wooden sill prate (Dodai) in Japan. The treatment consists of incising with specially designed blades and spraying with the solvent-based wood preservative. In the present investigation, we tried to apply this treatment to CLT panel. Laboratory scale test and full-scale test were carried out using 5-layer CLT panel with 150 mm thickness, 500 mm width and 800 mm length, and 150 mm thickness, 900 mm width and 3400 mm length, respectively. In the laboratory test, average penetration by the dip treatment was 98% in the 10 mm depth zone of central part of specimens, although wood preservative hardly penetrated into the inner layers. In the full-scale test, the penetration from wide face to 10 mm depth was 93% by the dip treatment and 90% by the surface treatment in the central part of the CLT. Penetration from the narrow face of the CLT was very low, probably due to the lack of incising. Although further evaluation and improvement are required for practical use, but the deep penetration treatment is expected to become one of the CLT preservation treatment methods.

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