Bora-Care can be applied to oriented strand board (OSB) that do has not be painted, stained or sealed per the manufacturer. Please refer to the product label for more detailed information by clicking the link below.
http://www.domyownpestcontrol.com/msds/boracare_label.pdf
Bora-Care is always the recommended product for treating active Powderpost Beetles because it penetrates deeper into the wood, up to 8 inches with 2 applications. Timbor will only go about 1/4 inch so it will not get to the larvae already in the wood. Bora-Care can take up to 30 days or more to penetrate all the way through a piece of wood and this will vary depending on how thick the wood is and the moisture content. We would recommend applying the Bora-Care and not a second application of Timbor. The larvae stage in the life of the Powderpost beetle is the longest, lasting from 1 to 10 years before it will mature to adulthood so it can take time to completely erradicate them.
Please take a moment to read over our article on How to Get Rid of Powderpost Beetles.