Not to be exposed to the elements, no You need pressure treated plywood for that. It can be used as sheathing on a building and covered with siding. I wouldn't use it as the siding. T-111 plywood is good for that as long as it is stained or painted. .

Good, detailed answer. Thanks.

installing ceramic tile in kitchen. Used 1/4 cement backer board with 1 1/4 inch Backer-on screws every 6 to 8 inches. Did not glue backer board to existing 9 year old floor 1st. Will I be OK?

maclorjoe,

You will not get any answers when posting your unrelated question in another discussion, it's called 'hijacking' but most people usually ask a sort of related question...

There is a specific kitchen forum, you could ask your question there, or in the bathroom forum (more discussion of tiling there.)_