I am re- pointing between patio slabs using soft sand and a standard cement.The cement recommends 1 : 5 but should it be 1:3 for these slabs? I
To give a quick answer, if you have masonry cement yes, 1 to 3 for the mix. If you have portland cement, it needs to stay at 1 to 5.
Portland is much stronger than masonry cement which has lime in it I believe. If you use too much portland with the sand, the mix will readily crack due to shrinkage.