I would like some advice deck is 450sq feet about 400 is under cover. I live in Portland Oregon The deck has been reinforced It is now 12'' centers 2x6 over 8' max span.
I am ready to start water proofing ? Cement board? Separator pad? Mastic ? Thinset?
Thanks Rob

Hi, I would sheet the deck with compressed cement sheeting, 18mm min, and make sure that you have fall to the outside of the deck. Do this by packing up the sheeting with battens no more than 600mm apart. 450mm is better. Screw the sheets down with brass or S/steel screws. Make sure that the sheets are flashed at the wall/floor junction. Silicone along under the flashing to make sure that no water gets under the flashing. Using a good water proofing agent, paint over the edge of the flashing and over the head of all the screws. You should be able to glue your tiles directly onto the sheeting with no problems.
Go for it!

Are you planning to install slate tile on a outside wooden deck?