Hey waggie, I'm a little late chiming in here, but if you're up for the task, you might try polymeric sand, sold under the trade names Gator Sand. There may be other brands out there by now. You could pressure wash the sand out of the crevices and replace it with the polymeric sand. Claims to be impervious to weeds. Another product they make is Gator Dust, a polymeric sand/aggregate mix made for larger crevices. If you are in a dry environment, this will probably work for you. It only worked for me for a few years, as I made the mistake of putting landscape cloth under the sand bed and additionally, my sidewalk is in a very wet, shady, freeze-thaw area. In hindsight, mortar might have fended off the weeds longer, but probably not. Again, if you live in a dry area, this polymeric sand seems to be current state of the art in paver applications. Here's sidewalk done.
Here's sidewalk in construction-puzzle pieces of our property's most abundant natural resource, large, flat rocks.
Another shot of rocks encased with Gator Dust (larger, aggregate product for big spaces).