[HayZee518]

before I laid floor tile in my bathroom shower pan, which is 3/4" OSB, joist spacing was 8 inches on center so I wouldn't get ANY flexing, I put down a layer of a sand/concrete mix in a ratio of 3 sand to 1 concrete and just enough of water to make a loose mix. This I put down and pounded it in place with a block of wood and a mallet. This set up overnight into a hard base. Then I used the quickset and tile, buttering each piece. For a floor your size this is sort of impractical so I'd go with the concrete board. It'll provide the teeth necessary to hold the quickset. allowing for tile spacing for floors 3/8-1/2 inch once the floor was down apply a good grout with a rubber float. wait a few days for the grout to set up and then examine the floor. if there's some cracks in the grout, make a thinner mixture of grout and water and hit it again filling in the cracks. then you should be good to go.