Paving Slabs - Apply Sand or use Sand and Cement?

[Mr Sparkle]

I have some paving slabs which i have pressure washed

Having scrapped out the weeds, I have many gaps that I wish to fill

What I want to know is whether you can just use kiln dried paving sand or whether I should be using building sand + cement (e.g. 4-1)?

 

[lonner]

Mortar would be best.
Mix damp "not wet" squeeze in your hand so it makes a firm ball and press in with a piece of thin wood ect, finish with a pointing iron, so it looks like brickwork.