Oriented Strand Board, or OSB, is a manufactured wood sheeting that can be used as a temporary substrate when creating a mosaic using lime putty.  OSB is inexpensive and does not easily absorb the moisture in the putty.  We don't sell OSB online since it is commonly available at building material centers like Home Depot and Lowes and the shipping costs are prohibitive.  We feature it here because customers ask us "what was that plywood-like board they used and where can I get it?"