Hi, I live in Northern VA and am installing dry laid 1.5" natural cleft flagstone on 4" of bluestone sub-base. I'd like this 500 sq ft. patio to last 20 years or more. My question:

Is it overkill to add 2" of stonedust as a base on top of the bluestone sub-base, or is this unnecessary? If my current plan is sub-optimal, I'm very open to feedback.

Thanks.

Is the 4" bluestone steppers or screenings? You do need a bed of screenings at least 2-4" deep. I think you may be using the term dust to describe screenings, it really is dusty but not plain dust.