Seriously! A saw-z-all, or resipricating saw, with a long pruning blade is my new favorite tool for carving cob. It’s fantastic for creating flush surfaces, rounding out corners and cutting niches into the wall. You can cut a pretty straight line with it too. Need a window? Carve it out. It gives you much more control then chiseling or hacking at the cob. Cob sure dulls the metal blade quickly though, but what do you expect.
The dust that it creates is pre-made cob mix, just add water.
I don’t think i’m going to spend as much time sculpting wet cob after using this tool for an afternoon. Not to say that chopping and smoothing while wet isn’t a good idea. Do as much as you can while it’s wet. After it is dry you can go in and sculpt it in moments. While building with cob there’s something to be said for just getting the cob on the wall, and then working out the details later. After all you want to save some time for the detail work.
Watch out though, you may carve off too much! When using power tools it’s pretty easy to get carried away.
Make sure to wear goggles, earplugs, dust mask and saftey gear with the saw-z-all. You will need it.

I’ve been using a non motorized pruning blade lately and that also works wonderfully! Quiter too.