Ceramic OSB sub-floor

I'm planning to install 12" ceramic tile in a kitchen and eating area. THe sub-floor is 19/32 OSB with 6" joists 16" o.c. I was going to use 1/4 Hardibacker but am not sure now because OSB is the sub-floor. Looking for recommendations on what is needed.

 

19/32 is way too thin for ceramic, and the deflection between the joists will kill the floor. Thick enough and osb is fine under cement boards, you just cannot tile directly to osb as thinset will not stick to it very long, but under cement board, the thinset is there to support the backer, not to bond it and the screws hold it down. Are you sure this is a single layer of 1/2" osb or is it an underlayment layer installed to build up the floor height? Drill a hole or remove a baseboard to find out for certain. Now your post at another forum indicated 2x6 joists spanning 12.5 feet. This wouldn't even support vinyl. Verify this info and post back. If you have a dishwasher, pull the bottom cover off and determine how much height you can add to the floor without dishwasher problems. See how much remaining adjustment you have for the feet too. There are other underlayment options that are thinner than cement board.

 

The floor is 3/4" OSB. The joists are 2 x 6 , 16" o.c . The max span is 7 feet. I have about 3/4" room remaing for the dishwasher.

 

Install 1/4" CBU over the OSB with unmodified thinset, then tile and tape the seams with Modified thinset, just remember, your at the minimum, more plywood is better, but you should be fine.

Dishwashers have ajustable legs on them.

 

Thanks, The 3/4' for the dishwasher took into consideration the leg adjustment.

 

As an FYI, in extreme cases, and as long as you make very certain the tile area under the dishwash is perfectly level, you can gain about 1/4" by removing the legs all together, eliminating the height of the feet. Thin felt pads will eliminate the issue of the metal casing scratching the tile.