Re: Tile on my covered deck?
2x6 boards?? You mean floor joists? And why only 2x6's?? Whats there now?
If you're going to tile the floor you have to be SURE there's no deflection in the floor which means using the appropriate sized floor joists for the span you have and also you should have TWO layers of WOOD subloor totaling a minimum of 1 1/4" thick and then you have to THINSET and screw down your CBU (cement boards).
OR instead of cement boards what I'd use in your case would be a product called DITRA. I'm enclosing a link for you as to where you can get it on line and they also have the installation PDF for you to look at.
I'd go this route rather than a cbu.Its a little more money than CBU's but its easier to install anddddddddd its better.