How much mortar to remove
 

I'm using the Kerdi membrane in a shower renovation. I'm using Ditra unmodified mortar and Hardi backer. The first 2 pieces of Kerdi I put up didn't hold well because I didn't wet the backerboard enough. I've removed the Kerdi. Question is how much mortar do I have to remove for rehanging the Kerdi? Do I need to scrape down to the backerboard if it is adhering well?

Thanks

How much mortar (square footage) did you put up?

If it isn't much, I would remove it and get back down to the back board.

It's about 36 square feet of coverage. What would you suggest- a scraper and sander?

Scraper.

You don't want to be breathing in mortar dust. Not good for the lung health with the portland and/or silica.

Ditto on the scraper. You don't want to be breathing CBU dust either.

How much effort did it take to pull it off?
I've never used Kerdi, but I suggest doing a bit more research. My understanding is even if done properly, it will be fairly easy to pull off. You may be fine the way you were doing it.

A scraper will work fine but I'd turn to my Fein MultiMaster with a blade made for removing mortar. My oscillating tool has become my favorite go-to tool. And prices for less expensive models are really reasonable.

It's not coming off very easily. I think I'm going to do a redo with some of it still adhering. I'm not going to get it all down to the backerboard.

its been a few years sinse i used kerdi. but back then they said to only use regular drywall.