Heavy stone veneer installation - interior - tips and tricks needed

I'm attempting to DIY a stone veneer fireplace surround, and I'm having trouble right out of the gate.

Here's the subject; 1/2" cement board screwed into the studs over the original sheetrock:

These are the stones, M-Rock "easy stack". They range from 1.5" to 2" thick, and are pretty heavy and rough on the backside.

I'm having trouble even getting the scratch coat started. I started with Rapid Set mortar, and it wasn't even sticking to the vertical surfaces. I also realized the fast cure time was going to be too quick for my work pace.

I switched to Quikrete Type S mortar, and while it seems to actually stick, when I use the notched trowel to apply texture it basically all comes off. 

Can/should I skip the scratch coat and just back-butter the stones? Did I mess up in applying cement board, should I be using steel lath instead? Is there perhaps a construction adhesive that would do the job considering this is an interior application? Any tips appreciated.

Since you are using cement board you don't need a scratch coat.  Just mortar the back of the stones and go to town.  Laticrete veneer mortar is a little easier to work with.

And make sure you're using the type of mortar recommended by both the backer board manufacturer and the stone manufacturer.  Call their technical service departments.

They don't call that stuff "lick and stick stone" for nothing.

While you're on the phone with the stone manufacturer, confirm that product is suitable for the temperature range you're expecting.  Unless you're aleady sure of that.

In reply to Duke :

The product installation guide specifies Type S mortar.

The stone shouldn't be exposed to much heat, the fireplace is actually a freestanding cast iron gas stove.

Alright, gave it a go with just back-buttered stones. Seems like it's working, still a little nervous about the initial holding power but we'll see if it all comes crashing down.

When they installed ours, they used cement board and steel plates to anchor and then an adhesive for the stone to the cement board. But ours was a different type of stone. 

In concstruction:

Completed:

For my fireplace I asked a million questions here.... then chickened out and hired a couple masons.  Watching them do it I realized that I would have totally messed it up.  Maybe not the mud part, but I would have failed at the placement of the natural stone.  I also would have used a hammer/chisel, but they used a diamond blade.  They said my type of natural stone would have just broken unpredictably.

I did mine with Hardie backer to the studs, then I did the scratch coat.... then called some pros.

I'm not a smart man, but it seems like some steel reinforcements holding the backer board to the wall would not be the terriblest of ideas

For vertical stucco stone stuff you really want one of these for a scratch coat.

The first thing I noticed was you have not finished the backerboard finishing of the seams,corners and screw holes. Just like drywalling for walls. You also may not have the correct mortar for adhering the stone to the backer boardhere are the instruction from USG  

https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.usg.com/content/dam/USG_Marketing_Communications/united_states/product_promotional_materials/finished_assets/usg-durock-cement-board-with-edgeguard-installation-guide-en-CB237EG.pdf&ved=2ahUKEwi2zYP78eb8AhWDHjQIHUaECawQFnoECBoQAQ&usg=AOvVaw1FHHpPNSC0h78y_zkYIlur

Butter the back. Stick them in place. Hold them in place with long drywall screws in the mortar joints until the Type S sets up. 
 

Remove screws, grout joints with a grout bag, enjoy. 
 

The tool you are missing is the screw gun. 

Also...

I think you will be much happier with the final results if you work both sides of the corner at the same time. 
 

In other words, work horizontally, not vertically. You want to try to fit all the stone pieces together on ALL the wall surfaces as you go up the walls, not build a column on one wall section then try to  tie into it around the corner. If you work vertically and then try to tie it in, you will get unnatural looking corners and seams.