I know this is confusing so here is a nice summary of the different types of limes available to consumers:
A quote from the above source:
Hydrated or ‘bag’ lime
This is the lime generally available in agricultural and builders merchants. It is a non-hydraulic lime produced by slaking Quicklime with a shortfall of water which results in a powder. It is generally considered to be an inferior product to the fat lime putty described above for a number of reasons but primarily because it starts to degrade from the moment it is made and can actually fully carbonate in the bag before use. Widespread use of ‘bag’ lime has given ‘lime’ a poor name because of the instances where it simply has none of its original properties left by the time the end-user works with it, hence it fails, dusts etc. If ‘bag’ lime is the only option, then it should be purchased as fresh as possible and left to soak for two days in clean water. Although the resulting product is chemically the same as ‘fat’ lime putty, it is physically different, in particular it is less ‘sticky’. A cement mix with a shovel of hydrated/bag lime in it is not a lime mortar, in this instance, the lime is simply being used as a plasticiser. It should not be used in pre-1919 buildings!
I would never use bagged lime for tataki. Ryan Chivers is playing russian roulette. Maybe his lime will recarbonate, maybe it won't. The last time I visited my parents, I found some lime test cylinders stored away in the basement. I made them when I was a civil engineering student in the 1980s and sure enough, they had recarbonated and seemed reasonably strong. If you review Simon's particular application, he wants to use lime mortar in a rammed earth wall and/or perhaps urbancrete using a typical type S bagged masons lime. In order for any non-hydraulic lime mortar to recarbonate, it must be exposed to atmosphere so it has access to CO2. Masons who have worked on buildings 100s of years old have reported that although the mortar on the surface (exposed) part of the wall had hardened, the mortar on the interior of the wall had not. That's because the interior part of the wall did not have a source of CO2 to recarbonate. So Simon's choices are to add Portland to his mix and make OPC mortar or add pozzolan to his lime so it becomes hydraulic. Hydraulic limes do not need exposure to the atmosphere to harden. Another option for him would be to use a Natural Hydraulic Lime. I haven't been able to find a source in the US, only europe, so that's why I had to make my own NHL. I sure wish a lime manufacturer would start offering NHL in the States. Maybe the natural building segment of the market is too small for them to bother with it but hopefully that will change with time.