What Type Of Sand Is Best For Cement Mix ?

Hi folks
I have a fairly old but good condition driveway made of granite slabs, but unfortunately a lot of weeds come up between many of the slabs. In places the gaps are maybe 1cm wide or more. I am planning to clear out these gaps and fill them with a 50-50 mixture of sand and cement - however my question is simply what would be the best type of sand to use - regular builders sand or sharp sand ? Or some other kind of sand ? I heard someone say builders sand would be better than sharp sand as sharp sand is rougher and the rougher edges would give something for the moss weeds to attach onto.

For example there are these on Wickes :-

https://www.wickes.co.uk/Tarmac-Sharp-Sand-Major-Bag/p/131881
https://www.wickes.co.uk/Yellow-Building-Sand-Major-Bag/p/131893

I have already done one line using sharp sand and it has set solid and seems OK, no weeds so far after about 4-5 weeks - but many weeds on the untreated gaps.

But overall what do you think would be the best choice ?

Thank you

I think i would go with the sharp assuming the cracks are not very thin, I would assume the larger grain size would have greater load bearing ability for a drive.

Mortar = building sand.

You will make a mess with sharp sa d as it won't hold the water.
Sharp sand will crack and look grainy too.

Three to one with a plasticiser will give best results.

Or go for a geofix type joint but they cost a bit but save time and mess

On the bit I have done I just mixed the sharp sand and cement dry, and filled it into the gap - it then sets with moisture from the ground and rainfall. It feels pretty solid, and I have hit it with a hammer and chisel as a test, and it only dents and crumbles a bit and does not crack.

If it were to crack later on I could fill in the cracks with something like these :-

Dansand No Weed Block Paving Sand Stone Dust - 20kg
https://www.wickes.co.uk/Dansand-No-Weed-Block-Paving-Sand-Stone-Dust---20kg/p/131899

Tarmac Weed Free Paving Sand - Major Bag
https://www.wickes.co.uk/Tarmac-Weed-Free-Paving-Sand---Major-Bag/p/175626

As these appear to be only for narrower gaps - whereas my gaps are pretty big - 1cm and over.

Or I could just fill in any cracks with building sand, or even dry sand/cement mix again as originally, as I don't know if there are any toxic chemicals like glyphosate in the above products.