I haven't a clue?

Mix is to strong, for something like that I would say 3 sand 1 cement, but make sure a proper 3.1 by measuring out the amounts in a bucket or whatever that suits the amounts she need, is she using a plasticizer in the mix.

As for where to buy, can't help you, only to say bulk buying is Way cheaper if its loose tipped off a truck.

 

Have you tried Builders Supply, Jewsons, Travis Perkins, Firwood, & Wickes. Can't think of anymore offhand.

Can't really comment on the mix.

 

Look under, for concrete.

https://en.m.wikipedia.org/wiki/Plasticizer



On the mix I forgot to add 1 stone as well,
10mm granite chipping.

So
3 sand
1 stone
1 cement

 

Great stuff hyper tufta, but put some reinforcement fibres in the mix like Adfill (polypropylene (PP) fibres), can buy in plastic bags, it will give the object some reinforcment. (Google concrete fibres)
Several mixes used, some use 'All in Ballast' at 3-1 mix, others use sharp sand again 3-1 & different amount of peat can be added depending on finish wanted, & some also add cement colouring

Papercrete is something you don't see much now over here now, seen it done 30 years ago, don't know much about it sadly, something I wanted to play with, but have never got around to it.
Surprisingly there a few video's on Youtube, quite popular other side of the pond & there plenty of ideas for
hypertufa on the tube.



http://www.alpinegardensociety.net/pdf_files/publication/AGS-Hypertufa_Leaflet.pdf

 

Would adding waterproofer also be a good idea? Help protect the objects survive a number of winters outdoors?

 

Wow - love the texture of these .

I'm guessing not weatherproof outside in the long term? Or, can it be modified to make it so?

 

Waterproof, but unlikely to be frostproof I would think.

Great stuff Adfill, can also get in paper bags, which just you throw in the mixer with each mix, paper disolves.
Casted a few window cills in situ a few years ago, used Adfill in the mix, as well as rebar to give the cills some extra strength.

http://cmga.caes.uga.edu/documents/HypertufaDirectionsReflections.pdf

Could use some Waterproofer admix or something like Evermix 204, 3 in 1 admix which waterproofs, plasticises & retards I would think.

And Pinterest is a good source of info for hyper-tufa.

https://uk.pinterest.com/mandolamama/hyper-tufa/

 

The main cause of them cracking is the damp soil freezing & expanding.
Might not be so much of a problem with smaller pots.

But, items like a butler sink which have been covered hyper tufta, doesn't seem to suffer from frost damage.
I remember reading somewhere, that if you are in a cold location, adjust the mix by lowering peat/volume, which would reduce frost damage.

 

Apparantly curing the hyper tufta it the biggest cause of failure from frost damage.
It can survive the Canadain winter without to much trouble.

http://www.bluefoxfarm.com/hypertufa-projects.html

Also look on your local Freecycle,Freegle for sharp sand, always peeps giving it away, or place a wanted ad for some.

 

To add to the handy tips, do not dry in direct beating sunlight (wait for the British comments) as the moisture will dry out before the cement is cured, and likewise do not let it frost over before the cement is cured or the moisture will freeze.