I was thinking about the mortar for your compressed block structures while I was doing stonework today. With masonry construction you always want to have a mortar that is softer than your brick so that when the building moves the mortar fails (which is easy to replace) rather than the blocks. In other words, if you rip a button of your shirt you want the thread to break and not the shirt. Same idea. With CEB this seems very difficult because of the relative softness of the bricks. The old limestone building that I'm working on has a mortar that consists of lime, sand (round river sand), and fly ash (a by product similar to cement). It's a soft mortar, but it's very resilient to movement. It weathers faster than modern mortars, but if your covering the structure with a lime render (as limestone buildings also were) that softness wouldn't be a big deal. I was also thinking that it would be wise to scrape your mortar joints back before they set so that the lime render has a place to key. I thought I would pass along my thoughts while they're fresh in my mind.