Durock cement backer-mesh tape with modified or unmodified thinset - Tile Advice

[roundrightfarm]

Greetings. I am putting in 2 showers with Durock brand cement board with Edgeguard. The instructions say to "fill joints with latex-modified mortar". I also have a Durock brand shower valve seal, where the instructional video says to use "unmodified thinset mortar" to attach it to the wall.

I was wondering if I could use unmodified thinset mortar to join the Durock cement board. I will be waterproofing afterward with Mapei Aquadefense and corner and edge cloth. Since I'm not using the thinset to attach tiles, does it matter what type I use on the cement board?

I'm also wondering if the shower valve seal is not meant to be used with cement board. In the video, it shows "Durock Shower System" board being used for the walls. This appears different than the regular cement board. Is this shower valve seal still compatible?

 

[Flintstone]

Can I hazard a guess that your in America ? Things are a little different over here.

 

[roundrightfarm]

good guess