Caporegime
What is your patio made of? We've just used easyjoint on 64sqm of smooth sandstone and it was fantastic. 10mm gaps and 1200x600 slabs used 4 tubs. Perfect finish and it was incredibly easy. Could probably do it in an hour and zero mess. We took about 2 hours and spent time running along each joing a few times with a pointing iron to really compact it in. Probably unnecessary though.
It's limestone.
900*600 slabs (that probably doesn't matter mind.
Good to know 4tubs worked for you though, some of the gaps will be smaller some larger on ours, so I'm tempted to try it.
I need to clean them up first probably as I made a bit of a mess laying them.