Hypertufa as stone

Rick, that sculpture would be fantastic in a trough!  Is it yours?

I think the only one of your questions I could comment on is the second:  
"Since hypertufa contains lime that leaches into surroundings, would a weathering period be wise before use?"  

I would think such a precaution would be unnecessary - it seems to me that most plants are quite insensitive to pH.  (An exception would be real calcifuges, of course, but then, one wouldn't be planting them in tufa or hypertufa anyway, I wouldn't think.)
A surprising amount of chalk dust (i.e. powdered lime) comes off tufa, but it does not seem that any weathering period is necessary.

Depending on the method used to make the hypertufa, it might involve underwater curing anyway.  (Our troughs sat filled with water and covered with plastic to cure, in order for the cement mix to develop its strength.)   So, some leaching out of "free" lime might happen, though I don't think it's necessary for the sake of the (appropriately-chosen) plants.

My thoughts, at any rate!!  Other viewpoints?

RickR wrote:

I never really thought about making hypertufa stones in quantity for a rock garden.  (Thanks for putting that in my head, Trond.) 

I have not made such things myself, but I have mixed concrete several times.

-- What issues would one need to be cognizant of while embarking on such an endeavor? 

You have to have all remedies ready before starting and you have to consider how to move the product which can be heavy?

-- Since hypertufa contains lime that leaches into surroundings, would a weathering period be wise before use? 

Wouldn't bother me. As Skulski says, you,ll grow lime tolerant plants anyway.

-- Any adjustments in the mix? 

Don't make the mix too lean (that is too little cement/mortar.

-- Would the hypertufa decompose faster or slower than above ground as troughs? 

I think it will decompose faster in the root zone as the roots produce H+ ions when changing cations with the soil.

-- Any experiences from you all out there?

As I said: Not with hypertufa! So my answers are educated guessing!

Yes, the sculpture is mine.  When I was making troughs, I had some leftover hypertufa to play with.  While in the soft stage, it took shape rather quickly with a power drill and cement bit.