Mixing your mortar

A lot to do with the sand and the moisture in it.

building sand in UK tends to be a lot finer and softer than here.

2mm. would be very coarse.

I'd say your man above is using soft sand, unlikely to be even 1mm.

That admix he uses would make it very putty-like,

nice for brick laying, I don't know about concrete blocks though.

He'd probably call 2mm. stuff sharp sand

I noticed the same watching Best Bricky - his mortar is like cream and his bricks slide into the mix. He's known to use a lot of plasticiser in the mix too and a lot of his mortar is red sand rather than the grey sand which we have here.

I got a batch of mortar sand from one of the providers in Dublin and it was like sharp-sand with no give in it and then the next batch was much creamier. I tried adding soft sand but I really think that most of it is down to the source of the sand - whether it was sourced from well rounded glacial alluvium or whether it contained lots of sharp/jagged sand.

Seems there's a spec for it.

https://www.concreteconstruction.net/how-to/mortar-mixing-time_o

"How long should a mortar be mixed? Should all ingredients be mixed at the same time? Most masons mix mortars using a paddle mixer. The appendix to ASTM C 270 Standard Specification for Mortar for Unit Masonry recommends that 3/4 of the required water, 1/2 the sand, and all the cementitious materials be briefly mixed together first. Then the balance of the sand and water is added. The mortar should be mixed a minimum of 3 minutes and a maximum of 5 minutes after the last water has been added to the mix. The standard states that overmixing can change the mortar's air content. The Reinforced Concrete Masonry Construction Inspectors Handbook, published by the Masonry Institute of America and the International Conference of Building Officials, says to mix mortar by first mixing 1/2 the water and 1/4 of the sand, then adding the cement, lime, color, and remaining water and sand. It recommends that all of the ingredients be mixed for not less than 3 nor more than 10 minutes"

So maybe it's the entrapment of the air that I miss out on by hand-mixing it, and that's the magic ingredient.