Can I use "Exposure 1" panels on a deck that will be covered with ceramic tile?
Here's the APA's take on this.
Exposure 1 Plywood Panels are suitable for uses not permanently exposed to weather. Panels classified as Exposure 1 are intended to resist the effects of moisture due to construction delays, or other conditions of similar severity. These panels are manufactured with the same fully waterproof glues as used in Exterior plywood; however, because of other compositional factors that may affect bond performance, only Exterior panels should be used for long-term exposure to weather. Exposure 1 panels may, however, be used where exposure to the outdoors is on the underside only, such as at roof overhangs.
APA Rated Sheathing Exposure 1 plywood, commonly called CDX, is oftentimes confused with an Exterior plywood panel and misused in applications. It is important to understand the difference between these classifications in order to select the best panel for your project.
Exposure 1 plywood has less voids, but the same glue. Otherwise the differences between it and rated sheathing are few.
You should not tile directly to the plywood!!!!! You must put down 1/2" tile backer. A waterproof membrane must be installed under the tile backer to prevent moisture from migrating to the plywood.