I am preparing to repaint a concrete patio. I am using a power washer to remove as much of 3 layers as I can.

The power washer has cleaned up the spaces between each slab very nicely, too. I can't believe how much dirt and gunk was in there.

My question: are these joint gaps supposed to be open all the way to the ground below or are they supposed to be filled with something?

Thanks

(Also, if anyone knows of any web sites for ideas/techniques for 'faux painting' concrete, please let me know. I'm hoping for sort of a stone look but not individual stones.)