ᐅ Wall barrier to protect the masonry from rising damp

Good day, the construction company told us that a single vapor barrier on the concrete slab is sufficient (36.5 Poroton). My question is: shouldn’t there be two? Isn’t the second vapor barrier no longer necessary because of the waterproof slurry at the base?
Best regards, Micha

A single layer of waterproof slurry is more than sufficient.