Ongoing field evaluation of Douglas-fir cross-laminated timber in a ground proximity protected test in Mississippi
Current design standards incorporate the use of preservative treated and naturally durable wood where conditions are suitable for deterioration, but treatment options for mass timber products, particularly, cross laminated timber (CLT) remain to be addressed. Termiticide treatment is a necessity for CLT structures, especially in southeastern climates. Wood species currently used to fabricate CLT are non-durable, and current design standards do not properly address incorporation of preservative treatments into these systems. In this study, 12” x 14” x 4” Douglas-fir CLT pieces were installed in a ground proximity protected test at the Harrison Experimental Forest (HEF), (Saucier, MS). Test samples were placed in sets of two in 30” x 30” subplots on bricks approximately 3-4” above soil and covered with ventilated waterproof covers. A total of 20 test pairs (40 total samples) with four different treatments were installed. The treatments consisted of a soil termiticide treatment, a preventive borate spray treatment at initiation, a remedial treatment with the spray-on borate one year post initiation and untreated controls. Soil below five pairs of samples was treated the with a soil termiticide (Termidor® SC). For the preventive borate at initiation treatment, one sample per pair of five other sets was treated with a spray-on borate preventative treatment (Bora-Care®). The remaining ten pairs were left as untreated controls. Temperature and humidity inside some of the covered units is being monitored throughout the test. The ten control sets will be examined for termite attack 12 months after installation. Five of the attacked sets will be treated with spray-on borate as a remedial treatment for active termite attack.