drop in tub deck

hello, i am putting in a drop in whirlpool tub i built the deck and covered with 3/4 exterior plywood and then put 1/2 in cement board screwed over that i did the joints and corners with fiberglass tape and thin set when i set the tub in the mortar bed the gap between the cement board and the tub lip is about 1 inch, my tile is 5/16 thick plus the thin set of 1/4 still leaves me almost 1/2 inch, should i caulk this or put another layer of cement board or ditra to lessen gap? sorry for the length of post any help greatly appreciated, thanks

If you use a medium bed mortar, you can use mortar to do this. A big but, though, it is a lot harder for the DIY'er to keep things nice and flat with a thick mortar bed underneath. How big are the tile? If they're at least 12x12", you can use the Tuscan leveling system to get them perfectly flat, but it is a fair investment for a small project. You can probably do it, but it takes longer. Check out www.johnbridge.com for tiling help.

You might want to consider a coat of Redgard on the cbu to help waterproof things.

Ditra XL would take up more of the height difference than the stock stuff, and if you use Kerdi-band on the seam(s), you could waterproof it at the same time.

thank you for the info

i was wondering about the ditra xl i have regular ditra on the floor and thought about using that like you said but was unsure if i should just put it on the deck or on the vertical side wall and the deck? the xl you mentioned is how thick?i sure appreciate the advice , this project has me nervous, also do you normally tile the vertical side first and then the floor? thanks again

DitraXL is 5/16" thick verses 2/16 (1/8") of 'regular' Ditra. I'd probably do the floor then the vertical - this way, the edge of the floor tile would be hidden. If you use one of Schluter's expansion joints there, it doesn't matter, since each tile's edge is installed onto the profile trim piece. These work well for the top edges so you don't need the more expensive bullnose tile, too.

tub

You want the thinnest caulk/grout line under the tub possible, so raise the deck until the thinset and tile are almost touching the bottom of the rim. Slide the tile under the rim when you install it.