Home Improvement Questions? Ask a Handyman for Answers
Welcome to Just Answer, my name is ***** ***** I will do my best to help you with your issue. If my initial response doesn’t answer your question then let me know and we can continue our conversation.I'm sorry to be the bearer of bad news but you can't use thinset on "green board" and you really should have used tile backer (Durock, Denshield, etc) not MR sheetrock in a shower. You can sand down the wall board but sand more than you need then coat the exposed gypsum with 5 minute EasySand (< click on the link) mastic doesn't bond well to gypsum. You also need to use ceramic tie mastichttp://www.homedepot.com/p/Custom-Building-Products-AcrylPro-1-Gal-Ceramic-Tile-Adhesive-ARL40001/100015587
If you decide to stay with the MR sheet rock.
Yes you must use the AcrylPro not the thinset on MR wallboard. And yes you'll need to sand down the high spots if you want the tile to set flat. But the mastic won't bond well to the gypsum under the paper so that why I said you should coat the gypsum. You can use joint compound it just takes a lot longer to dry then EasySand 5
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