Flooring Tile - concrete board

i just finished putting up durarock around my hot tub. I am using 8 by 10 inch cerimac tile. I realised that my top bullnose piece is gonna be abot a inch shy of my joint which goes from rock to greenboard.. so my ? is can i tape that joint with sheetrock to hide the concrete board or am i screwed . i cant adjust my tile any higher because of window sills.any suggestions. also should i use a mastic for the tiles or a mortar..thanks

Sure, you can tape and mud the joint between the two. I prefer to use the setting type compound when going over cement boards. It's powdered, plaster based, and sets in minutes. It's advantagious due to the thirsty nature of cement boards since joint compound in a bucket is more likely to crack when drying over cbu. Setting type compound comes bagged, mixed with water, and the number on the bag indicates how many minutes until initial cure is reached. My local supply house has 5, 20, 45 and 90 minute varieties.


Always use bagged modified thinset in wet areas. Mastic does reemulsify when exposed to moisture over time. You did use 6 mil poly or 15 lb roffing felt over the studs prior to the cbu, correct?

Hey Thanks for the reply I havent been around to ,even check my emails..but yes indeed I got 6 mill back there..thanks again