Remodeling a bathroom and about to put in the floor. I have a plywood subfloor, and I'm about to install 1/2-in cement board on top, bedded in modified thinset spread with a quarter inch notched trowel. I plan to leave a 1/8-in in gap between all cement board sheets on the floor, with a 1/4-in gap at the walls. I'll be using a mosaic floor tile, and a subway tile on the walls with a cove base transition.
My tub is a porcelain enameled steel tub. It is solidly installed with the flange anchored on top of a ledge at the back of the wall. It is set into a bed of mortar which supports the entire base.
I have looked everywhere, but I can't seem to find any information as to how to properly transition the cement board on the floor with the skirt/apron/decorative panel of the tub. I have small kids that will definitely create splashes. Ideally I'll wipe them up quickly, but there will certainly be situations where the chaos of life leaves small puddles on the bathroom floor every now and then. I know of several people that have had issues with leaks from standing water at this transition point.
My thought is to leave an 1/8-in gap, and then fill that with thinset right up against the edge of the tub. Because I will be using Mapei Aqua Defense under the tile inside of the shower/tub enclosure, I could also apply a coat of this up against the edge of the tub at least, if not the entire bathroom floor (very small, 4x6 ft). I would then install tile as normal, leaving a 1/8-in gap, and caulking with 100% silicone or a siliconized grout matching caulk.
Does this make sense? Should I be doing anything different here? Another idea was leaving the 1/8-in gap open (cement board and tile), and filling the entire gap with silicone after installing tile.