u/Slap-A-Beaver

I've been doing paver re-sanding for close to 10 years and I have never seen this. These are grey pavers with grey sand and just underneath the sand is a beige substance that is hard as a rock. There was only a small amount of grey sand, 1/4inch at most and it was incredibly difficult to power wash out. The beige stuff wouldn't come out. Is this resin sand?

I want to do this job correctly. Should I just get the grey sand out and sweep new over the beige?