We built a concrete stone walkway using a form but are unhappy with the cracks letting weeds through and the unevenness of it. Would polymeric sand be a good filler?

Sand will do 0 to keep weeds out.
Use total vegatation killer.
Should work for a year.

polymeric sand is plastic glue and sand. get it wet, it plasticizes.

which keeps weeds out from the top, but not underneath. if they can break up parking lot and driveway concrete, they can break through poly sand.

you have to prevent weed seeds below from coming up, too. a chemical kills-all with landscape fabric should just about do it.

I just used some of the polymeric sand this past weekend. I'm not happy with how it turned out and it is horribly expensive to boot. It did well in the larger spaces, but not in the narrow spots between the pavers. It hardened well in the larger openings, but I don't think it is worth the price.