I was out early yesterday morning to try and beat the South Carolina heat but, I swear, it warmed up too quickly.
I experimented, substituting builder’s lime for joint compound: two parts sand, one part cement, one half part builder’s lime. No paper. Using a two pound coffee can for measuring and mixing the dry ingredients in a five gallon bucket, then hand mixing small portions with water in another bucket to make small batches. Very nice, smooth, clay-like feel to this mix. Sticks nicely. I was able to sculpt a little with it, but mostly used it as plaster. I am interested in deleting cellulose insulation in a mix because I want to try to add finer detail in future work. It seems to be curing nicely despite the heat. The bottom photo shows the section covered with this mix.
The most difficult aspect of mixing this mortar involves water. It is so easy to mix in too much water. It's best when the mix is damp and crumbly. I found that making sure I had a bit of dry mix left was the key. Then I could add some dry mix to a batch I'd made too wet..
With the mix damp and crumbly, I can dip my hand in water and work a handful iinto what feels like a ball of clay.