jtay yeah, Easyjoint.
Get the patio area drenched in water, break the 12.5kg bag open and unload it on the patio area, soak it with water to create a slurry and brush in. It's easier with a 2nd person watering behind you, to clear off loose 'sand' from the slabs. I was on my own, so the watering whilst doing the job and clearing off loose stuff wasnt easy. I've actually ended up brushing some of the excess off the slabs that has dried this lunchtime.
I ordered 4 tubs of mushroom-coloured online, not cheap, used 3, so have a spare. Delivered in 24 hours.