*Article* **Physical, Optical, and Visual Performance of Coated Cross-Laminated Timber during Natural and Artificial Weathering**

**Gabrielly dos Santos Bobadilha 1,\*, C. Elizabeth Stokes 1, Katie M. Ohno 2, Grant Kirker 2, Dercilio Junior Verly Lopes <sup>1</sup> and Mojgan Nejad <sup>3</sup>**


**Abstract:** Cross-laminated timber (CLT) market demand is on the rise in the United States. Adequate protective measures have not been extensively studied. The objective of this study was to investigate the weathering performance of exterior wood coatings. We evaluated coated CLT sample surfaces based on visual appearance, color change (CIE\*L\*a\*b), gloss changes, and water intrusion. From the five exterior wood coatings evaluated, only two showed adequate performance after twelve months field exposure. Based on visual ratings following the ASTM procedures, coating failure occurs more quickly in Mississippi than in Wisconsin, due to its greater decay zone. Both location and coating type impacted the aging of the samples. Artificial weathering results were consistent with natural weathering indicating the two adequate coatings were the most resistant to failure, color, and gloss change. For future studies, new coatings designed for the protection of end-grain in CLT panels should be a target of research and development.

**Keywords:** mass-timber; surface protection; outdoor exposure; wood degradation; cross-laminated timber
