I have had private chats using G+ posts and I attest that they never turned public. Once you make a post, you can't change it's visibility. You can only delete

I have had private chats using G+ posts and I attest that they never turned public. Once you make a post, you can't change it's visibility. You can only delete it, or lock it down - comments or reshares. Though I think gPlus + Wave would be the ideal such environment for me.